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SubjectRe: [PATCH v3 3/7] locking/pvqspinlock: Collect slowpath lock statistics
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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