On 19/11/12 14:09, Vincent Guittot wrote:
On 19 November 2012 14:36, Morten Rasmussen morten.rasmussen@arm.com wrote:
On 19/11/12 12:23, Vincent Guittot wrote:
On 19 November 2012 13:08, Morten Rasmussen morten.rasmussen@arm.com wrote:
Hi Vincent,
On 19/11/12 09:20, Vincent Guittot wrote:
Hi,
On 16 November 2012 19:32, Liviu Dudau Liviu.Dudau@arm.com wrote:
From: Morten Rasmussen morten.rasmussen@arm.com
Re-enable SD_SHARE_POWERLINE to reflect the power domains of TC2.
arch/arm/kernel/topology.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c index 317dac6..4d34e0e 100644 --- a/arch/arm/kernel/topology.c +++ b/arch/arm/kernel/topology.c @@ -228,7 +228,7 @@ struct cputopo_arm cpu_topology[NR_CPUS];
int arch_sd_share_power_line(void) {
return 0*SD_SHARE_POWERLINE;
return 1*SD_SHARE_POWERLINE;I'm not sure to catch your goal. With this modification, the power line (or power domain) is shared at all level which should disable the packing mechanism. But in a previous patch you fix the update packing loop so I assume that you want to use it. Which kind of configuration you would like to have among the proposal below ?
cpu : CPU0 | CPU1 | CPU2 | CPU3 | CPU4 buddy conf 1 : CPU2 | CPU0 | CPU2 | CPU2 | CPU2 buddy conf 2 : CPU2 | CPU2 | CPU2 | CPU2 | CPU2 buddy conf 3 : -1 | -1 | -1 | -1 | -1
When we look at the git://git.linaro.org/arm/big.LITTLE/mp.git big-LITTLE-MP-master-v12, we can see that you have defined a custom sched_domain which hasn't been updated with SD_SHARE_POWERLINE flag so the flag is cleared at CPU level. Based on this, I would say that you want buddy conf 2 ? but I would say that buddy conf 1 should give better result. Have you tried both ?
My goal with this fix is to set up the SD_SHARE_POWERLINE flags as they really are on TC2. It could have been done more elegantly. Since the HMP patches overrides the sched_domain flags at CPU level the SD_SHARE_POWERLINE is not being set by arch_sd_share_power_line(). With this fix we will get SD_SHARE_POWERLINE at MC level and no SD_SHARE_POWERLINE at CPU level, which I believe is the correct set up for TC2.
For the buddy configuration the goal is to get configuration 1 in your list above. You should get that when using the other patch to fix the buddy selection algorithm. I'm not sure if conf 1 or 2 is best. I think it depends on the power/performance trade-off of the specific platform. conf 1 may lead to CPU1->CPU0->CPU2 migrations which may be undesirable. If your cpus are very leaky it might make sense to not do packing at all inside a high performance cluster and always do packing directly on a another low power cluster like conf 2. I think this needs further investigation.
I have only tested with conf 1 on TC2.
Hi Morten,
Conf1 is the default configuration for ARM platform because SD_SHARE_POWERLINE is cleared at all levels for this architecture.
Conf2 should be used if you can't powergate the core independently but several tests have demonstrated that even if you can't powergate each core independently, it worth packing small task on few CPUs in a core so it's worth using conf1 on TC2 as well.
Based on your explanation, we should use the original configuration of SD_SHARE_POWERLINE (cleared at all level for ARM platform)
I agree that the result is the same, but I don't like disabling SD_SHARE_POWERLINE for all level when the cpus in each cluster actually are in the same power domain as it is the case on TC2. The name SHARE_POWERLINE implies a clear relation to the actual hardware design, thus setting the flags differently than the actual hardware design is misleading in my opinion. If the buddy selection algorithm doesn't select appropriate buddies when flags are set to reflect the actual hardware design I would suggest changing the buddy selection algorithm instead of changing the sched_domain flags.
If it is chosen to not have a direct relation between the flags and the hardware design, I think that the flag should be renamed so it doesn't give the wrong impression.
There is a direct link between the powergating and the SHARE_POWERLINE and if you want that the buddy selection strictly reflects your HW configuration, you must use conf2 and not conf1.
I just want the buddy selection to be reasonable when the SHARE_POWERLINE flags are reflecting the true hardware configuration. I haven't tested whether conf 1 or 2 is best yet. As long as I am getting one them it is definitely an improvement over not having task packing at all :)
Now, beside the packing small task patch and the TC2 configuration, it has been proven that packing small tasks on an ARM platform (dual cortex-A9) which can only powergate the cluster, improves the power consumption of some low cpu load use cases like the MP3 playback (we had used cpu hotplug at that time). This assumption has been proven only for ARM platform and that's why the SHARE_POWERLINE is cleared at all level for ARM platform even if you can only do some WFI inside the cluster.
Yes, but other cpus may be significantly more expensive to have in WFI so the power difference between WFI and running some lightweight task might be small. In that case it could make sense to spread tasks instead and hope for more opportunities for cluster shutdown. I haven't got any proof of this being correct yet, but I think it is worth considering.
Morten
But i agree that if you want to strictly reflect the TC2 HW config, you should use the conf2 and set the SHARE_POWERLINE at MC level for the TC2 HMP configuration
Regards, Vincent
Morten
Regards Vincent
Regards, Morten
Regards, Vincent
} const struct cpumask *cpu_coregroup_mask(int cpu)-- 1.7.9.5
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