Messages in this thread Patch in this message | | | Date | Fri, 29 Aug 2008 18:45:15 +0530 | From | Vaidyanathan Srinivasan <> | Subject | sched_mc_power_savings broken with CGROUPS+CPUSETS |
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Hi,
sched_mc_power_savings seems to be broken with CGROUPS+CPUSETS. When CONFIG_CPUSETS=y the attached BUG_ON() is being hit.
I added a BUG_ON to check if SD_POWERSAVINGS_BALANCE is set at SD_LV_CPU whenever sched_mc_power_savings is set.
This BUG is hit when config CONFIG_CPUSETS (depends on CONFIG_CGROUPS) is just compiled in while this is never hit when they are compiled out. The fact that SD_POWERSAVINGS_BALANCE being cleared even when sched_mc_power_savings = 1 completely breaks the sched_mc_power_savings heuristics.
To recreate the problem, Have sched_mc power savings enabled CONFIG_SCHED_MC=y Add this BUG_ON()
echo 1 > /sys/devices/system/cpu/sched_mc_power_savings
Try these these on a multi core x86 box.
sched_mc_power_savings seems to be broken from 2.6.26-rc1, but I do not have a confirmation that the root cause is same in all successive versions. sched_mc_power_savings works perfect in 2.6.25.
Please help me root cause the issue. Please point me to changes that may potential cause this bug.
Thanks, Vaidy
Signed-off-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Index: linux-2.6.27-rc5/kernel/sched.c =================================================================== --- linux-2.6.27-rc5.orig/kernel/sched.c 2008-08-29 17:48:56.000000000 +0000 +++ linux-2.6.27-rc5/kernel/sched.c 2008-08-29 18:16:09.000000000 +0000 @@ -3375,6 +3375,8 @@ out_balanced: #if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT) + BUG_ON(sched_mc_power_savings && sd->level == SD_LV_CPU && + !(sd->flags & SD_POWERSAVINGS_BALANCE)); if (idle == CPU_NOT_IDLE || !(sd->flags & SD_POWERSAVINGS_BALANCE)) goto ret;
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