Messages in this thread | | | Date | Mon, 27 Jul 2015 13:33:53 -0400 | From | Waiman Long <> | Subject | Re: [PATCH v3 3/7] locking/pvqspinlock: Collect slowpath lock statistics |
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On 07/26/2015 09:14 PM, Davidlohr Bueso wrote: > On Wed, 2015-07-22 at 16:12 -0400, Waiman Long wrote: >> This patch enables the accumulation of kicking and waiting related >> PV qspinlock statistics when the new QUEUED_LOCK_STAT configuration >> option is selected. It also enables the collection of kicking and >> wakeup latencies which have a heavy dependency on the CPUs being used. >> >> The measured latencies for different CPUs are: >> >> CPU Wakeup Kicking >> --- ------ ------- >> Haswell-EX 89.8us 7.4us >> Westmere-EX 67.6us 9.3us >> > But you don't mention anything about the overhead of enabling > QUEUED_LOCK_STAT. This does several atomic ops, thus potentially > thrashing workloads. >
Yes, QUEUED_LOCK_STAT will slow performance a bit. It is like enabling LOCK_STAT and you will expect some slow down too. It is essentially a debugging option to see what had actually happened in the system. It should be turned off in a production system.
Cheers, Longman
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