linux-kernel - Re: [RFC PATCH] sched: Introduce per-mm/cpu concurrency id state

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Date:   Mon, 3 Apr 2023 14:17:53 -0400
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Aaron Lu <aaron.lu@...el.com>
Cc:     Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] sched: Introduce per-mm/cpu concurrency id state

On 2023-03-31 04:52, Aaron Lu wrote:
> On Thu, Mar 30, 2023 at 07:09:11PM -0400, Mathieu Desnoyers wrote:
>> Keep track of the currently allocated mm_cid for each mm/cpu rather than
>> freeing them immediately. This eliminates most atomic ops when context
>> switching back and forth between threads belonging to different memory
>> spaces in multi-threaded scenarios (many processes, each with many
>> threads).
> 
> Good news, the lock contention is now gone and back to v6.2 level:

Hi Aaron,

Can you please test the updated patch I've sent ? I have updated the
subject to make it clear that this is a fix for a performance regression,
improved comments, and it now passes more thorough testing. See:

https://lore.kernel.org/lkml/20230403181342.210896-1-mathieu.desnoyers@efficios.com/

Thanks,

Mathieu

> 
> node0_0.profile:     0.07%     0.07%  [kernel.vmlinux]        [k] native_queued_spin_lock_slowpath
> node0_1.profile:     0.06%     0.06%  [kernel.vmlinux]        [k] native_queued_spin_lock_slowpath
> node0_2.profile:     0.09%     0.09%  [kernel.vmlinux]        [k] native_queued_spin_lock_slowpath
> node0_3.profile:     0.08%     0.08%  [kernel.vmlinux]        [k] native_queued_spin_lock_slowpath
> node0_4.profile:     0.09%     0.09%  [kernel.vmlinux]        [k] native_queued_spin_lock_slowpath
> node0_5.profile:     0.10%     0.10%  [kernel.vmlinux]        [k] native_queued_spin_lock_slowpath
> node0_6.profile:     0.10%     0.10%  [kernel.vmlinux]        [k] native_queued_spin_lock_slowpath
> node0_7.profile:     0.07%     0.07%  [kernel.vmlinux]        [k] native_queued_spin_lock_slowpath
> node0_8.profile:     0.08%     0.08%  [kernel.vmlinux]        [k] native_queued_spin_lock_slowpath
> node0_9.profile:     0.06%     0.06%  [kernel.vmlinux]        [k] native_queued_spin_lock_slowpath
> node1_0.profile:     0.41%     0.41%  [kernel.vmlinux]        [k] native_queued_spin_lock_slowpath
> node1_1.profile:     0.38%     0.38%  [kernel.vmlinux]        [k] native_queued_spin_lock_slowpath
> node1_2.profile:     0.44%     0.44%  [kernel.vmlinux]        [k] native_queued_spin_lock_slowpath
> node1_3.profile:     5.64%     5.64%  [kernel.vmlinux]        [k] native_queued_spin_lock_slowpath
> node1_4.profile:     6.08%     6.08%  [kernel.vmlinux]        [k] native_queued_spin_lock_slowpath
> node1_5.profile:     3.45%     3.45%  [kernel.vmlinux]        [k] native_queued_spin_lock_slowpath
> node1_6.profile:     2.09%     2.09%  [kernel.vmlinux]        [k] native_queued_spin_lock_slowpath
> node1_7.profile:     2.72%     2.72%  [kernel.vmlinux]        [k] native_queued_spin_lock_slowpath
> node1_8.profile:     0.16%     0.16%  [kernel.vmlinux]        [k] native_queued_spin_lock_slowpath
> node1_9.profile:     0.15%     0.15%  [kernel.vmlinux]        [k] native_queued_spin_lock_slowpath
> (those few profiles from node1's cpus that have more than 2% contention
> are from thermal functions)
> 
> Tested-by: Aaron Lu <aaron.lu@...el.com> # lock contention part




-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com