lkml.org 
[lkml]   [2015]   [Sep]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v6 4/6] locking/pvqspinlock: Collect slowpath lock statistics
On 09/14/2015 05:41 PM, Davidlohr Bueso wrote:
> On Mon, 14 Sep 2015, Waiman Long wrote:
>
>> You can't use debugfs if we want to have per-cpu stats. We will have
>> to use sysfs instead. This will require more code changes. It is
>> certainly doable, but we have to choose between simplicity and
>> performance overhead. Right now, I am assuming that lock PV lockstat
>> is used primarily for debugging purpose and won't be enabled on
>> production system. If we want to have this capability in production
>> systems, we will certainly need to change it to per-cpu stats and use
>> sysfs instead.
>>
>> The original PV ticketlock code used debugfs and I was just following
>> its footstep. Do you think it is worthwhile to have this capability
>> available on production system by default?
>
> If we can prove that the overhead is small enough, and do it correctly
> (ie see how we do vmstats), it would be _very_ useful data to have
> enabled by default for debugging performance issues; methinks. But right
> now we have nowhere near that kind of data, not even with this atomic
> variant -- although I recall you did mention a workload in a previous
> iteration (which would be good to have in the changelog).

Using the per-cpu stats, the overhead should be pretty small as atomic
instructions are not needed. I would probably need to encapsulate the
stat code into another header file (e.g. qspinlock_pvstat.h) to avoid
making the qspinlock_paravirt.h too complex. This will probably be a
separate patch once this patch series can be merged.

Cheers,
Longman


\
 
 \ /
  Last update: 2015-09-15 06:01    [W:0.121 / U:0.068 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site