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Re: [PATCH 00/11] locking/ww_mutex: Keep sorted wait list to avoid stampedes

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On 30.11.2016 10:40, Chris Wilson wrote:
> On Mon, Nov 28, 2016 at 01:20:01PM +0100, Nicolai Hähnle wrote:
>> I've included timings taken from a contention-heavy stress test to some of
>> the patches. The stress test performs actual GPU operations which take a
>> good chunk of the wall time, but even so, the series still manages to
>> improve the wall time quite a bit.
>
> In looking at your contention scenarios, what was the average/max list
> size? Just wondering if it makes sense to use an rbtree + first_waiter
> instead of a sorted list from the start.

I haven't measured this with the new series; previously, while I was 
debugging the deadlock on older kernels, I occasionally saw wait lists 
of up to ~20 tasks, spit-balling the average over all the deadlock cases 
I'd say the average was not more than ~5. The average _without_ 
deadlocks should be lower, if anything.

I saw that your test cases go quite a bit higher, but even the rather 
extreme load I was testing with -- which is not quite a load from an 
actual application, though it is related to one -- has 40 threads and so 
a theoretical maximum of 40.

Nicolai

> -Chris
>

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[PATCH 00/11] locking/ww_mutex: Keep sorted wait list to avoid stampedes Nicolai Hähnle <nhaehnle@gmail.com> - 2016-11-28 13:30 +0100
  [PATCH 2/4] locking: Add kselftests for ww_mutex AA deadlock detection Chris Wilson <chris@chris-wilson.co.uk> - 2016-11-30 01:40 +0100
  [PATCH 4/4] locking: Add kselftests for ww_mutex stress Chris Wilson <chris@chris-wilson.co.uk> - 2016-11-30 01:40 +0100
    Re: [PATCH 4/4] locking: Add kselftests for ww_mutex stress Maarten Lankhorst <dev@mblankhorst.nl> - 2016-11-30 13:30 +0100
      Re: [PATCH 4/4] locking: Add kselftests for ww_mutex stress Chris Wilson <chris@chris-wilson.co.uk> - 2016-11-30 14:00 +0100
  [PATCH 1/4] locking: Begin kselftests for ww_mutex Chris Wilson <chris@chris-wilson.co.uk> - 2016-11-30 01:40 +0100
    [PATCH 3/4] locking: Add kselftests for ww_mutex ABBA deadlock detection Chris Wilson <chris@chris-wilson.co.uk> - 2016-11-30 01:40 +0100
    Re: [PATCH 1/4] locking: Begin kselftests for ww_mutex Nicolai Hähnle <nhaehnle@gmail.com> - 2016-11-30 09:10 +0100
  Re: [PATCH 00/11] locking/ww_mutex: Keep sorted wait list to avoid  stampedes Chris Wilson <chris@chris-wilson.co.uk> - 2016-11-30 10:50 +0100
    Re: [PATCH 00/11] locking/ww_mutex: Keep sorted wait list to avoid  stampedes Nicolai Hähnle <nhaehnle@gmail.com> - 2016-11-30 13:10 +0100
      Re: [PATCH 00/11] locking/ww_mutex: Keep sorted wait list to avoid  stampedes Chris Wilson <chris@chris-wilson.co.uk> - 2016-11-30 13:30 +0100
        Re: [PATCH 00/11] locking/ww_mutex: Keep sorted wait list to avoid  stampedes Nicolai Hähnle <nhaehnle@gmail.com> - 2016-11-30 14:50 +0100

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