Greetings,
This is a RFC for a maintenance patch to an issue in the amd_pstate driver where CPU frequency cannot be boosted in passive or guided modes. Without this patch, AMD machines using stable kernels are unable to get their CPU frequency boosted, which is a significant performance issue.
For example, on a host that has AMD EPYC 7662 64-Core processor without this patch running at full CPU load:
$ for i in $(cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq); \ do ni=$(echo "scale=1; $i/1000000" | bc -l); echo "$ni GHz"; done | \ sort | uniq -c
128 2.0 GHz
And with this patch:
$ for i in $(cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq); \ do ni=$(echo "scale=1; $i/1000000" | bc -l); echo "$ni GHz"; done | \ sort | uniq -c
128 3.3 GHz
I am not sure what the correct process is for submitting patches which affect only stable trees but not the current code base, and do not apply to the current tree. As such, I am submitting this directly to stable@, but please let me know if I should be submitting this elsewhere.
The issue was introduced in v6.1 via commit bedadcfb011f ("cpufreq: amd-pstate: Fix initial highest_perf value"), and exists in stable kernels up until v6.6.51.
In v6.6.51, a large change, commit 1ec40a175a48 ("cpufreq: amd-pstate: Enable amd-pstate preferred core support"), was introduced which significantly refactored the code. This commit cannot be ported back on its own, and would require reviewing and cherry picking at least a few dozen of commits in cpufreq, amd-pstate, ACPI, CPPC.
This means kernels v6.1 up until v6.6.51 are affected by this significant performance issue, and cannot be easily remediated.
Thank you for your attention and I look forward to your response in regards to what the best way to proceed is for getting this important performance fix merged.
Best Regards,
Nabil S. Alramli (1): cpufreq: amd-pstate: Enable CPU boost in passive and guided modes
drivers/cpufreq/amd-pstate.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-)
The CPU frequency cannot be boosted when using the amd_pstate driver in passive or guided mode. This is fixed here.
The CPU frequency is dependent on a setting called highest_perf which is the multiplier used to compute it. The highest_perf value comes from cppc_init_perf when the driver is built-in and from pstate_init_perf when it is a loaded module. Both of these calls have the following condition:
highest_perf = amd_get_highest_perf(); if (highest_perf > __cppc_highest_perf_) highest_perf = __cppc_highest_perf;
Where again __cppc_highest_perf is either the return from cppc_get_perf_caps in the built-in case or AMD_CPPC_HIGHEST_PERF in the module case. Both of these functions actually return the nominal value, Whereas the call to amd_get_highest_perf returns the correct boost value, so the condition tests true and highest_perf always ends up being the nominal value, therefore never having the ability to boost CPU frequency.
Since amd_get_highest_perf already returns the boost value we should just eliminate this check.
Signed-off-by: Nabil S. Alramli dev@nalramli.com Fixes: bedadcfb011f ("cpufreq: amd-pstate: Fix initial highest_perf value") See-also: 1ec40a175a48 ("cpufreq: amd-pstate: Enable amd-pstate preferred core support") Cc: Perry.Yuan@amd.com Cc: li.meng@amd.com Cc: stable@vger.kernel.org # 6.1 - v6.6.50 --- drivers/cpufreq/amd-pstate.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-)
diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c index 90dcf26f0973..c66086ae624a 100644 --- a/drivers/cpufreq/amd-pstate.c +++ b/drivers/cpufreq/amd-pstate.c @@ -102,9 +102,7 @@ static int pstate_init_perf(struct amd_cpudata *cpudata) * * CPPC entry doesn't indicate the highest performance in some ASICs. */ - highest_perf = amd_get_highest_perf(); - if (highest_perf > AMD_CPPC_HIGHEST_PERF(cap1)) - highest_perf = AMD_CPPC_HIGHEST_PERF(cap1); + highest_perf = max(amd_get_highest_perf(), AMD_CPPC_HIGHEST_PERF(cap1));
WRITE_ONCE(cpudata->highest_perf, highest_perf);
@@ -124,9 +122,7 @@ static int cppc_init_perf(struct amd_cpudata *cpudata) if (ret) return ret;
- highest_perf = amd_get_highest_perf(); - if (highest_perf > cppc_perf.highest_perf) - highest_perf = cppc_perf.highest_perf; + highest_perf = max(amd_get_highest_perf(), cppc_perf.highest_perf);
WRITE_ONCE(cpudata->highest_perf, highest_perf);
[AMD Official Use Only - AMD Internal Distribution Only]
-----Original Message----- From: Nabil S. Alramli dev@nalramli.com Sent: Friday, October 25, 2024 9:05 AM To: stable@vger.kernel.org Cc: nalramli@fastly.com; jdamato@fastly.com; khubert@fastly.com; Yuan, Perry Perry.Yuan@amd.com; Meng, Li (Jassmine) Li.Meng@amd.com; Huang, Ray Ray.Huang@amd.com; rafael@kernel.org; viresh.kumar@linaro.org; linux- pm@vger.kernel.org; linux-kernel@vger.kernel.org; Nabil S. Alramli dev@nalramli.com Subject: [RFC PATCH 6.1.y 0/1] cpufreq: amd-pstate: Enable CPU boost in passive and guided modes
Greetings,
This is a RFC for a maintenance patch to an issue in the amd_pstate driver where CPU frequency cannot be boosted in passive or guided modes. Without this patch, AMD machines using stable kernels are unable to get their CPU frequency boosted, which is a significant performance issue.
For example, on a host that has AMD EPYC 7662 64-Core processor without this patch running at full CPU load:
$ for i in $(cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq); \ do ni=$(echo "scale=1; $i/1000000" | bc -l); echo "$ni GHz"; done | \ sort | uniq -c
128 2.0 GHzAnd with this patch:
$ for i in $(cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq); \ do ni=$(echo "scale=1; $i/1000000" | bc -l); echo "$ni GHz"; done | \ sort | uniq -c
128 3.3 GHzI am not sure what the correct process is for submitting patches which affect only stable trees but not the current code base, and do not apply to the current tree. As such, I am submitting this directly to stable@, but please let me know if I should be submitting this elsewhere.
The issue was introduced in v6.1 via commit bedadcfb011f ("cpufreq: amd-pstate: Fix initial highest_perf value"), and exists in stable kernels up until v6.6.51.
In v6.6.51, a large change, commit 1ec40a175a48 ("cpufreq: amd-pstate: Enable amd-pstate preferred core support"), was introduced which significantly refactored the code. This commit cannot be ported back on its own, and would require reviewing and cherry picking at least a few dozen of commits in cpufreq, amd-pstate, ACPI, CPPC.
This means kernels v6.1 up until v6.6.51 are affected by this significant performance issue, and cannot be easily remediated.
Thank you for your attention and I look forward to your response in regards to what the best way to proceed is for getting this important performance fix merged.
Best Regards,
Nabil S. Alramli (1): cpufreq: amd-pstate: Enable CPU boost in passive and guided modes
drivers/cpufreq/amd-pstate.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-)
-- 2.35.1
Add Mario and Gautham for any help.
Perry.
On 10/24/2024 22:23, Yuan, Perry wrote:
[AMD Official Use Only - AMD Internal Distribution Only]
-----Original Message----- From: Nabil S. Alramli dev@nalramli.com Sent: Friday, October 25, 2024 9:05 AM To: stable@vger.kernel.org Cc: nalramli@fastly.com; jdamato@fastly.com; khubert@fastly.com; Yuan, Perry Perry.Yuan@amd.com; Meng, Li (Jassmine) Li.Meng@amd.com; Huang, Ray Ray.Huang@amd.com; rafael@kernel.org; viresh.kumar@linaro.org; linux- pm@vger.kernel.org; linux-kernel@vger.kernel.org; Nabil S. Alramli dev@nalramli.com Subject: [RFC PATCH 6.1.y 0/1] cpufreq: amd-pstate: Enable CPU boost in passive and guided modes
Greetings,
This is a RFC for a maintenance patch to an issue in the amd_pstate driver where CPU frequency cannot be boosted in passive or guided modes. Without this patch, AMD machines using stable kernels are unable to get their CPU frequency boosted, which is a significant performance issue.
For example, on a host that has AMD EPYC 7662 64-Core processor without this patch running at full CPU load:
$ for i in $(cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq); \ do ni=$(echo "scale=1; $i/1000000" | bc -l); echo "$ni GHz"; done | \ sort | uniq -c
128 2.0 GHzAnd with this patch:
$ for i in $(cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq); \ do ni=$(echo "scale=1; $i/1000000" | bc -l); echo "$ni GHz"; done | \ sort | uniq -c
128 3.3 GHzI am not sure what the correct process is for submitting patches which affect only stable trees but not the current code base, and do not apply to the current tree. As such, I am submitting this directly to stable@, but please let me know if I should be submitting this elsewhere.
The issue was introduced in v6.1 via commit bedadcfb011f ("cpufreq: amd-pstate: Fix initial highest_perf value"), and exists in stable kernels up until v6.6.51.
In v6.6.51, a large change, commit 1ec40a175a48 ("cpufreq: amd-pstate: Enable amd-pstate preferred core support"), was introduced which significantly refactored the code. This commit cannot be ported back on its own, and would require reviewing and cherry picking at least a few dozen of commits in cpufreq, amd-pstate, ACPI, CPPC.
This means kernels v6.1 up until v6.6.51 are affected by this significant performance issue, and cannot be easily remediated.
Thank you for your attention and I look forward to your response in regards to what the best way to proceed is for getting this important performance fix merged.
Best Regards,
Nabil S. Alramli (1): cpufreq: amd-pstate: Enable CPU boost in passive and guided modes
drivers/cpufreq/amd-pstate.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-)
-- 2.35.1
Add Mario and Gautham for any help.
Perry.
If doing a patch that is only for 6.1.y then I think that some more of this information from the cover letter needs to push into the patch itself.
But looking over the patch and considering how much we've changed this in the newer kernels I think it is a sensible localized change for 6.1.y.
As this is fixed in 6.6.51 via a more complete backport patch please only tag 6.1 in your "Cc: stable@vger.kernel.org" from the patch.
Hi Mario,
Thank you for taking a look at my patch.
What do you think about the following for the commit message in the next revision of the PATCH, and omitting the cover letter since most of it is incorporated here?
***********************************************************************
cpufreq: amd-pstate: Enable CPU boost in passive and guided modes
The CPU frequency cannot be boosted when using the amd_pstate driver in passive or guided mode. This is fixed here.
For example, on a host that has AMD EPYC 7662 64-Core processor without this patch running at full CPU load:
$ for i in $(cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq); \ do ni=$(echo "scale=1; $i/1000000" | bc -l); echo "$ni GHz"; done | \ sort | uniq -c
128 2.0 GHz
And with this patch:
$ for i in $(cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq); \ do ni=$(echo "scale=1; $i/1000000" | bc -l); echo "$ni GHz"; done | \ sort | uniq -c
128 3.3 GHz
The CPU frequency is dependent on a setting called highest_perf which is the multiplier used to compute it. The highest_perf value comes from cppc_init_perf when the driver is built-in and from pstate_init_perf when it is a loaded module. Both of these calls have the following condition:
highest_perf = amd_get_highest_perf(); if (highest_perf > __cppc_highest_perf_) highest_perf = __cppc_highest_perf;
Where again __cppc_highest_perf is either the return from cppc_get_perf_caps in the built-in case or AMD_CPPC_HIGHEST_PERF in the module case. Both of these functions actually return the nominal value, Whereas the call to amd_get_highest_perf returns the correct boost value, so the condition tests true and highest_perf always ends up being the nominal value, therefore never having the ability to boost CPU frequency.
Since amd_get_highest_perf already returns the boost value we should just eliminate this check.
The issue was introduced in v6.1 via commit bedadcfb011f ("cpufreq: amd-pstate: Fix initial highest_perf value"), and exists in stable kernels
In v6.6.51, a large change, commit 1ec40a175a48 ("cpufreq: amd-pstate: Enable amd-pstate preferred core support"), was introduced which significantly refactored the code. This commit cannot be ported back on its own, and would require reviewing and cherry picking at least a few dozen of commits in cpufreq, amd-pstate, ACPI, CPPC.
This means kernels v6.1 up until v6.6.51 are affected by this significant performance issue, and cannot be easily remediated. This patch simplifies the fix to a single commit.
***********************************************************************
On 10/28/2024 4:07 PM, Mario Limonciello wrote:
On 10/24/2024 22:23, Yuan, Perry wrote:
[AMD Official Use Only - AMD Internal Distribution Only]
-----Original Message----- From: Nabil S. Alramli dev@nalramli.com Sent: Friday, October 25, 2024 9:05 AM To: stable@vger.kernel.org Cc: nalramli@fastly.com; jdamato@fastly.com; khubert@fastly.com; Yuan, Perry Perry.Yuan@amd.com; Meng, Li (Jassmine) Li.Meng@amd.com; Huang, Ray Ray.Huang@amd.com; rafael@kernel.org; viresh.kumar@linaro.org; linux- pm@vger.kernel.org; linux-kernel@vger.kernel.org; Nabil S. Alramli dev@nalramli.com Subject: [RFC PATCH 6.1.y 0/1] cpufreq: amd-pstate: Enable CPU boost in passive and guided modes
Greetings,
This is a RFC for a maintenance patch to an issue in the amd_pstate driver where CPU frequency cannot be boosted in passive or guided modes. Without this patch, AMD machines using stable kernels are unable to get their CPU frequency boosted, which is a significant performance issue.
For example, on a host that has AMD EPYC 7662 64-Core processor without this patch running at full CPU load:
$ for i in $(cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq); \ do ni=$(echo "scale=1; $i/1000000" | bc -l); echo "$ni GHz"; done | \ sort | uniq -c
128 2.0 GHz
And with this patch:
$ for i in $(cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq); \ do ni=$(echo "scale=1; $i/1000000" | bc -l); echo "$ni GHz"; done | \ sort | uniq -c
128 3.3 GHz
I am not sure what the correct process is for submitting patches which affect only stable trees but not the current code base, and do not apply to the current tree. As such, I am submitting this directly to stable@, but please let me know if I should be submitting this elsewhere.
The issue was introduced in v6.1 via commit bedadcfb011f ("cpufreq: amd-pstate: Fix initial highest_perf value"), and exists in stable kernels up until v6.6.51.
In v6.6.51, a large change, commit 1ec40a175a48 ("cpufreq: amd-pstate: Enable amd-pstate preferred core support"), was introduced which significantly refactored the code. This commit cannot be ported back on its own, and would require reviewing and cherry picking at least a few dozen of commits in cpufreq, amd-pstate, ACPI, CPPC.
This means kernels v6.1 up until v6.6.51 are affected by this significant performance issue, and cannot be easily remediated.
Thank you for your attention and I look forward to your response in regards to what the best way to proceed is for getting this important performance fix merged.
Best Regards,
Nabil S. Alramli (1): cpufreq: amd-pstate: Enable CPU boost in passive and guided modes
drivers/cpufreq/amd-pstate.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-)
-- 2.35.1
Add Mario and Gautham for any help.
Perry.
If doing a patch that is only for 6.1.y then I think that some more of this information from the cover letter needs to push into the patch itself.
But looking over the patch and considering how much we've changed this in the newer kernels I think it is a sensible localized change for 6.1.y.
As this is fixed in 6.6.51 via a more complete backport patch please only tag 6.1 in your "Cc: stable@vger.kernel.org" from the patch.
On 10/28/2024 16:33, Nabil S. Alramli wrote:
Hi Mario,
Thank you for taking a look at my patch.
What do you think about the following for the commit message in the next revision of the PATCH, and omitting the cover letter since most of it is incorporated here?
cpufreq: amd-pstate: Enable CPU boost in passive and guided modes
The CPU frequency cannot be boosted when using the amd_pstate driver in passive or guided mode. This is fixed here.
No need to say things like "I did this" or "this patch does that". Just drop last sentence.
For example, on a host that has AMD EPYC 7662 64-Core processor without this patch running at full CPU load:
"On a host that has an AMD EPYC 7662 processor while running with amd-pstate configured for passive mode on full CPU load the processor only reaches 2.0 GHz."
$ for i in $(cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq); \ do ni=$(echo "scale=1; $i/1000000" | bc -l); echo "$ni GHz"; done | \ sort | uniq -c
128 2.0 GHzAnd with this patch:
On later kernels the CPU can reach 3.3GHz.
$ for i in $(cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq); \ do ni=$(echo "scale=1; $i/1000000" | bc -l); echo "$ni GHz"; done | \ sort | uniq -c
128 3.3 GHzThe CPU frequency is dependent on a setting called highest_perf which is the multiplier used to compute it. The highest_perf value comes from cppc_init_perf when the driver is built-in and from pstate_init_perf when it is a loaded module. Both of these calls have the following condition:
highest_perf = amd_get_highest_perf(); if (highest_perf > __cppc_highest_perf_) highest_perf = __cppc_highest_perf;Where again __cppc_highest_perf is either the return from cppc_get_perf_caps in the built-in case or AMD_CPPC_HIGHEST_PERF in the module case. Both of these functions actually return the nominal value, Whereas the call to amd_get_highest_perf returns the correct boost value, so the condition tests true and highest_perf always ends up being the nominal value, therefore never having the ability to boost CPU frequency.
Since amd_get_highest_perf already returns the boost value we should just eliminate this check.
The issue was introduced in v6.1 via commit bedadcfb011f ("cpufreq: amd-pstate: Fix initial highest_perf value"), and exists in stable kernels
"In stable 6.1" kernels.
In v6.6.51, a large change, commit 1ec40a175a48 ("cpufreq: amd-pstate: Enable amd-pstate preferred core support"), was introduced which significantly refactored the code. This commit cannot be ported back on its own, and would require reviewing and cherry picking at least a few dozen of commits in cpufreq, amd-pstate, ACPI, CPPC.
I'd just say "this has been fixed in 6.6.y and newer but due to refactoring that change isn't feasible to bring back to 6.1.y"
This means kernels v6.1 up until v6.6.51 are affected by this significant performance issue, and cannot be easily remediated. This patch simplifies the fix to a single commit.
Again no need to say "this patch".
On 10/28/2024 4:07 PM, Mario Limonciello wrote:
On 10/24/2024 22:23, Yuan, Perry wrote:
[AMD Official Use Only - AMD Internal Distribution Only]
-----Original Message----- From: Nabil S. Alramli dev@nalramli.com Sent: Friday, October 25, 2024 9:05 AM To: stable@vger.kernel.org Cc: nalramli@fastly.com; jdamato@fastly.com; khubert@fastly.com; Yuan, Perry Perry.Yuan@amd.com; Meng, Li (Jassmine) Li.Meng@amd.com; Huang, Ray Ray.Huang@amd.com; rafael@kernel.org; viresh.kumar@linaro.org; linux- pm@vger.kernel.org; linux-kernel@vger.kernel.org; Nabil S. Alramli dev@nalramli.com Subject: [RFC PATCH 6.1.y 0/1] cpufreq: amd-pstate: Enable CPU boost in passive and guided modes
Greetings,
This is a RFC for a maintenance patch to an issue in the amd_pstate driver where CPU frequency cannot be boosted in passive or guided modes. Without this patch, AMD machines using stable kernels are unable to get their CPU frequency boosted, which is a significant performance issue.
For example, on a host that has AMD EPYC 7662 64-Core processor without this patch running at full CPU load:
$ for i in $(cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq); \ do ni=$(echo "scale=1; $i/1000000" | bc -l); echo "$ni GHz"; done | \ sort | uniq -c
128 2.0 GHz
And with this patch:
$ for i in $(cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq); \ do ni=$(echo "scale=1; $i/1000000" | bc -l); echo "$ni GHz"; done | \ sort | uniq -c
128 3.3 GHz
I am not sure what the correct process is for submitting patches which affect only stable trees but not the current code base, and do not apply to the current tree. As such, I am submitting this directly to stable@, but please let me know if I should be submitting this elsewhere.
The issue was introduced in v6.1 via commit bedadcfb011f ("cpufreq: amd-pstate: Fix initial highest_perf value"), and exists in stable kernels up until v6.6.51.
In v6.6.51, a large change, commit 1ec40a175a48 ("cpufreq: amd-pstate: Enable amd-pstate preferred core support"), was introduced which significantly refactored the code. This commit cannot be ported back on its own, and would require reviewing and cherry picking at least a few dozen of commits in cpufreq, amd-pstate, ACPI, CPPC.
This means kernels v6.1 up until v6.6.51 are affected by this significant performance issue, and cannot be easily remediated.
Thank you for your attention and I look forward to your response in regards to what the best way to proceed is for getting this important performance fix merged.
Best Regards,
Nabil S. Alramli (1): cpufreq: amd-pstate: Enable CPU boost in passive and guided modes
drivers/cpufreq/amd-pstate.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-)
-- 2.35.1
Add Mario and Gautham for any help.
Perry.
If doing a patch that is only for 6.1.y then I think that some more of this information from the cover letter needs to push into the patch itself.
But looking over the patch and considering how much we've changed this in the newer kernels I think it is a sensible localized change for 6.1.y.
As this is fixed in 6.6.51 via a more complete backport patch please only tag 6.1 in your "Cc: stable@vger.kernel.org" from the patch.
Mario,
Thank you so much for your valuable feedback. This all makes sense, and I will incorporate it into another revision soon.
On 10/29/2024 12:09 AM, Mario Limonciello wrote:
On 10/28/2024 16:33, Nabil S. Alramli wrote:
Hi Mario,
Thank you for taking a look at my patch.
What do you think about the following for the commit message in the next revision of the PATCH, and omitting the cover letter since most of it is incorporated here?
cpufreq: amd-pstate: Enable CPU boost in passive and guided modes
The CPU frequency cannot be boosted when using the amd_pstate driver in passive or guided mode. This is fixed here.
No need to say things like "I did this" or "this patch does that". Just drop last sentence.
My apologies. I was just trying to be clear as to what this patch does. I will drop it.
For example, on a host that has AMD EPYC 7662 64-Core processor without this patch running at full CPU load:
"On a host that has an AMD EPYC 7662 processor while running with amd-pstate configured for passive mode on full CPU load the processor only reaches 2.0 GHz."
$ for i in $(cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq); \ do ni=$(echo "scale=1; $i/1000000" | bc -l); echo "$ni GHz"; done | \ sort | uniq -c
128 2.0 GHz
And with this patch:
On later kernels the CPU can reach 3.3GHz.
$ for i in $(cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq); \ do ni=$(echo "scale=1; $i/1000000" | bc -l); echo "$ni GHz"; done | \ sort | uniq -c
128 3.3 GHz
The CPU frequency is dependent on a setting called highest_perf which is the multiplier used to compute it. The highest_perf value comes from cppc_init_perf when the driver is built-in and from pstate_init_perf when it is a loaded module. Both of these calls have the following condition:
highest_perf = amd_get_highest_perf(); if (highest_perf > __cppc_highest_perf_) highest_perf = __cppc_highest_perf;
Where again __cppc_highest_perf is either the return from cppc_get_perf_caps in the built-in case or AMD_CPPC_HIGHEST_PERF in the module case. Both of these functions actually return the nominal value, Whereas the call to amd_get_highest_perf returns the correct boost value, so the condition tests true and highest_perf always ends up being the nominal value, therefore never having the ability to boost CPU frequency.
Since amd_get_highest_perf already returns the boost value we should just eliminate this check.
The issue was introduced in v6.1 via commit bedadcfb011f ("cpufreq: amd-pstate: Fix initial highest_perf value"), and exists in stable kernels
"In stable 6.1" kernels.
In v6.6.51, a large change, commit 1ec40a175a48 ("cpufreq: amd-pstate: Enable amd-pstate preferred core support"), was introduced which significantly refactored the code. This commit cannot be ported back on its own, and would require reviewing and cherry picking at least a few dozen of commits in cpufreq, amd-pstate, ACPI, CPPC.
I'd just say "this has been fixed in 6.6.y and newer but due to refactoring that change isn't feasible to bring back to 6.1.y"
This means kernels v6.1 up until v6.6.51 are affected by this significant performance issue, and cannot be easily remediated. This patch simplifies the fix to a single commit.
Again no need to say "this patch".
Understood. As I stated this was just for clarity as to why the patch may be needed or useful.
On 10/28/2024 4:07 PM, Mario Limonciello wrote:
On 10/24/2024 22:23, Yuan, Perry wrote:
[AMD Official Use Only - AMD Internal Distribution Only]
-----Original Message----- From: Nabil S. Alramli dev@nalramli.com Sent: Friday, October 25, 2024 9:05 AM To: stable@vger.kernel.org Cc: nalramli@fastly.com; jdamato@fastly.com; khubert@fastly.com; Yuan, Perry Perry.Yuan@amd.com; Meng, Li (Jassmine) Li.Meng@amd.com; Huang, Ray Ray.Huang@amd.com; rafael@kernel.org; viresh.kumar@linaro.org; linux- pm@vger.kernel.org; linux-kernel@vger.kernel.org; Nabil S. Alramli dev@nalramli.com Subject: [RFC PATCH 6.1.y 0/1] cpufreq: amd-pstate: Enable CPU boost in passive and guided modes
Greetings,
This is a RFC for a maintenance patch to an issue in the amd_pstate driver where CPU frequency cannot be boosted in passive or guided modes. Without this patch, AMD machines using stable kernels are unable to get their CPU frequency boosted, which is a significant performance issue.
For example, on a host that has AMD EPYC 7662 64-Core processor without this patch running at full CPU load:
$ for i in $(cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq); \ do ni=$(echo "scale=1; $i/1000000" | bc -l); echo "$ni GHz"; done | \ sort | uniq -c
128 2.0 GHz
And with this patch:
$ for i in $(cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq); \ do ni=$(echo "scale=1; $i/1000000" | bc -l); echo "$ni GHz"; done | \ sort | uniq -c
128 3.3 GHz
I am not sure what the correct process is for submitting patches which affect only stable trees but not the current code base, and do not apply to the current tree. As such, I am submitting this directly to stable@, but please let me know if I should be submitting this elsewhere.
The issue was introduced in v6.1 via commit bedadcfb011f ("cpufreq: amd-pstate: Fix initial highest_perf value"), and exists in stable kernels up until v6.6.51.
In v6.6.51, a large change, commit 1ec40a175a48 ("cpufreq: amd-pstate: Enable amd-pstate preferred core support"), was introduced which significantly refactored the code. This commit cannot be ported back on its own, and would require reviewing and cherry picking at least a few dozen of commits in cpufreq, amd-pstate, ACPI, CPPC.
This means kernels v6.1 up until v6.6.51 are affected by this significant performance issue, and cannot be easily remediated.
Thank you for your attention and I look forward to your response in regards to what the best way to proceed is for getting this important performance fix merged.
Best Regards,
Nabil S. Alramli (1): cpufreq: amd-pstate: Enable CPU boost in passive and guided modes
drivers/cpufreq/amd-pstate.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-)
-- 2.35.1
Add Mario and Gautham for any help.
Perry.
If doing a patch that is only for 6.1.y then I think that some more of this information from the cover letter needs to push into the patch itself.
But looking over the patch and considering how much we've changed this in the newer kernels I think it is a sensible localized change for 6.1.y.
As this is fixed in 6.6.51 via a more complete backport patch please only tag 6.1 in your "Cc: stable@vger.kernel.org" from the patch.
linux-stable-mirror@lists.linaro.org
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Mario Limonciello -
Nabil S. Alramli -
Yuan, Perry