[PATCH] Documentation/no_hz: Remove description that states boot CPU cannot be nohz_full
From: Oleg Nesterov oleg@redhat.com
[ Upstream commit 5097cbcb38e6e0d2627c9dde1985e91d2c9f880e ]
Documentation/timers/no_hz.rst states that the "nohz_full=" mask must not include the boot CPU, which is no longer true after:
commit 08ae95f4fd3b ("nohz_full: Allow the boot CPU to be nohz_full").
Apply changes only to Documentation/timers/no_hz.rst in stable kernels.
Signed-off-by: Oleg Nesterov oleg@redhat.com Cc: stable@vger.kernel.org # 5.4+ Signed-off-by: Krishanth Jagaduri Krishanth.Jagaduri@sony.com --- Hi,
Before kernel 6.9, Documentation/timers/no_hz.rst states that "nohz_full=" mask must not include the boot CPU, which is no longer true after commit 08ae95f4fd3b ("nohz_full: Allow the boot CPU to be nohz_full").
This was fixed upstream by commit 5097cbcb38e6 ("sched/isolation: Prevent boot crash when the boot CPU is nohz_full").
While it fixes the document description, it also fixes issue introduced by another commit aae17ebb53cd ("workqueue: Avoid using isolated cpus' timers on queue_delayed_work").
It is unlikely that it will be backported to stable kernels which does not contain the commit that introduced the issue.
Could Documentation/timers/no_hz.rst be fixed in stable kernels 5.4+? --- Documentation/timers/no_hz.rst | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-)
diff --git a/Documentation/timers/no_hz.rst b/Documentation/timers/no_hz.rst index 065db217cb04fc252bbf6a05991296e7f1d3a4c5..16bda468423e88090c0dc467ca7a5c7f3fd2bf02 100644 --- a/Documentation/timers/no_hz.rst +++ b/Documentation/timers/no_hz.rst @@ -129,11 +129,8 @@ adaptive-tick CPUs: At least one non-adaptive-tick CPU must remain online to handle timekeeping tasks in order to ensure that system calls like gettimeofday() returns accurate values on adaptive-tick CPUs. (This is not an issue for CONFIG_NO_HZ_IDLE=y because there are no running -user processes to observe slight drifts in clock rate.) Therefore, the -boot CPU is prohibited from entering adaptive-ticks mode. Specifying a -"nohz_full=" mask that includes the boot CPU will result in a boot-time -error message, and the boot CPU will be removed from the mask. Note that -this means that your system must have at least two CPUs in order for +user processes to observe slight drifts in clock rate.) Note that this +means that your system must have at least two CPUs in order for CONFIG_NO_HZ_FULL=y to do anything for you.
Finally, adaptive-ticks CPUs must have their RCU callbacks offloaded.
--- base-commit: 219d54332a09e8d8741c1e1982f5eae56099de85 change-id: 20250129-send-oss-20250129-3c42dcf463eb
Best regards,
On Wed, Feb 05, 2025 at 08:32:14AM +0530, Krishanth Jagaduri via B4 Relay wrote:
From: Oleg Nesterov oleg@redhat.com
[ Upstream commit 5097cbcb38e6e0d2627c9dde1985e91d2c9f880e ]
It's just the documentation part of that commit, not the full one.
Documentation/timers/no_hz.rst states that the "nohz_full=" mask must not include the boot CPU, which is no longer true after:
commit 08ae95f4fd3b ("nohz_full: Allow the boot CPU to be nohz_full").
Apply changes only to Documentation/timers/no_hz.rst in stable kernels.
You dropped the rest of the changelog text here :(
Signed-off-by: Oleg Nesterov oleg@redhat.com Cc: stable@vger.kernel.org # 5.4+ Signed-off-by: Krishanth Jagaduri Krishanth.Jagaduri@sony.com
And you dropped all the other signed-off-by lines :(
Hi,
Before kernel 6.9, Documentation/timers/no_hz.rst states that "nohz_full=" mask must not include the boot CPU, which is no longer true after commit 08ae95f4fd3b ("nohz_full: Allow the boot CPU to be nohz_full").
This was fixed upstream by commit 5097cbcb38e6 ("sched/isolation: Prevent boot crash when the boot CPU is nohz_full").
While it fixes the document description, it also fixes issue introduced by another commit aae17ebb53cd ("workqueue: Avoid using isolated cpus' timers on queue_delayed_work").
It is unlikely that it will be backported to stable kernels which does not contain the commit that introduced the issue.
Could Documentation/timers/no_hz.rst be fixed in stable kernels 5.4+?
Does the documentation lines really matter here?
At the very least, we can't take this as the signed-off-by lines are all gone. Please resend with them all back, and then make a note that you are only including the documentation portion and why.
thanks,
greg k-h
On Wed, Feb 05, 2025 at 10:18:17AM +0100, Greg KH wrote:
On Wed, Feb 05, 2025 at 08:32:14AM +0530, Krishanth Jagaduri via B4 Relay wrote:
From: Oleg Nesterov oleg@redhat.com
[ Upstream commit 5097cbcb38e6e0d2627c9dde1985e91d2c9f880e ]
It's just the documentation part of that commit, not the full one.
Updated in v2. Thank you.
Documentation/timers/no_hz.rst states that the "nohz_full=" mask must not include the boot CPU, which is no longer true after:
commit 08ae95f4fd3b ("nohz_full: Allow the boot CPU to be nohz_full").
Apply changes only to Documentation/timers/no_hz.rst in stable kernels.
You dropped the rest of the changelog text here :(
Updated in v2. Thank you.
Signed-off-by: Oleg Nesterov oleg@redhat.com Cc: stable@vger.kernel.org # 5.4+ Signed-off-by: Krishanth Jagaduri Krishanth.Jagaduri@sony.com
And you dropped all the other signed-off-by lines :(
Updated in v2. Thank you.
While it fixes the document description, it also fixes issue introduced by another commit aae17ebb53cd ("workqueue: Avoid using isolated cpus' timers on queue_delayed_work").
It is unlikely that it will be backported to stable kernels which does not contain the commit that introduced the issue.
Could Documentation/timers/no_hz.rst be fixed in stable kernels 5.4+?
Does the documentation lines really matter here?
When we tried LTS kernels 5.4 to 6.6, we noticed that boot CPU can be nohz_full without any problems. But information in documentation was misleading. We wanted to check if it would be okay to fix the information in the document.
At the very least, we can't take this as the signed-off-by lines are all gone. Please resend with them all back, and then make a note that you are only including the documentation portion and why.
Updated in v2. Thank you.
Best regards, Krishanth
[ Sasha's backport helper bot ]
Hi,
The upstream commit SHA1 provided is correct: 5097cbcb38e6e0d2627c9dde1985e91d2c9f880e
WARNING: Author mismatch between patch and upstream commit: Backport author: Krishanth Jagaduri via B4 Relaydevnull+Krishanth.Jagaduri.sony.com@kernel.org Commit author: Oleg Nesterovoleg@redhat.com
Status in newer kernel trees: 6.13.y | Present (exact SHA1)
Note: The patch differs from the upstream commit: --- Failed to apply patch cleanly, falling back to interdiff... ---
Results of testing on various branches:
| Branch | Patch Apply | Build Test | |---------------------------|-------------|------------| | stable/linux-6.13.y | Failed | N/A | | stable/linux-6.12.y | Failed | N/A | | stable/linux-6.6.y | Success | Failed | | stable/linux-6.1.y | Success | Failed | | stable/linux-5.15.y | Success | Failed | | stable/linux-5.10.y | Success | Failed | | stable/linux-5.4.y | Success | Failed |
Build Errors: Build error for stable/linux-6.6.y: ssh: connect to host 192.168.1.58 port 22: No route to host
Build error for stable/linux-6.1.y: ssh: connect to host 192.168.1.58 port 22: No route to host
Build error for stable/linux-5.15.y: ssh: connect to host 192.168.1.58 port 22: No route to host
Build error for stable/linux-5.10.y: ssh: connect to host 192.168.1.58 port 22: No route to host
Build error for stable/linux-5.4.y: ssh: connect to host 192.168.1.58 port 22: No route to host
linux-stable-mirror@lists.linaro.org
-
Greg KH -
Krishanth Jagaduri -
Krishanth Jagaduri via B4 Relay -
Sasha Levin