Messages in this thread | | | Date | Thu, 31 Jul 2014 18:58:46 -0400 | From | Prarit Bhargava <> | Subject | Re: [PATCH] cpufreq, store_scaling_governor requires policy->rwsem to be held for duration of changing governors [v2] |
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On 07/31/2014 06:13 PM, Saravana Kannan wrote: > On 07/31/2014 02:08 PM, Prarit Bhargava wrote: >> >> >> On 07/31/2014 04:38 PM, Saravana Kannan wrote: >>> On 07/31/2014 01:30 PM, Prarit Bhargava wrote: >>>> >>>> >>>> On 07/31/2014 04:24 PM, Saravana Kannan wrote: >>>>> >>>>> Prarit, >>>>> >>>>> I'm not an expert on sysfs locking, but I would think the specific sysfs lock >>>>> would depend on the file/attribute group. So, can you please try to hotplug a >>>>> core in/out (to trigger the POLICY_EXIT) and then read a sysfs file >>>>> exported by >>>>> the governor? scaling_governor doesn't cut it since that file is not >>>>> removed on >>>>> policy exit event to governor. If it's ondemand, try reading/write it's >>>>> sampling >>>>> rate file. >>>> >>>> Thanks Saravana -- will do. I will get back to you shortly on this. >>>> >>> >>> Thanks. Btw, in case you weren't already aware of it. You'll have to hoplug out >>> all the CPUs in a cluster to trigger a POLICY_EXIT for that cluster/policy. >> >> Yep -- the affected_cpus file should show all the cpus in the policy IIRC. One >> of the systems I have has 1 cpu/policy and has 48 threads so the POLICY_EXIT is >> called. >> >> I'll put something like >> >> while [1]; >> do >> echo ondemand > /sys/devices/system/cpu/cpu1/cpufreq/scaling_governor >> cat /sys/devices/system/cpu/cpufreq/ondemand/sampling_rate >> echo 20000 > /sys/devices/system/cpu/cpufreq/ondemand/sampling_rate >> cat /sys/devices/system/cpu/cpufreq/ondemand/sampling_rate >> echo 0 > /sys/devices/system/cpu/cpu1/online >> sleep 1 >> echo 1 > /sys/devices/system/cpu/cpu1/online >> sleep 1 >> done >> > > The actual race can only happen with 2 threads. I'm just trying to trigger a > lockdep warning here.
I ran the above in two separate terminals with cpuset -c 0 and cpuset -c 1 to multi-thread it all. No deadlock or LOCKDEP trace after about 1/2 hour, so I think we're in the clear on that concern.
P.
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