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

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Message-ID: <20230331085229.GB186694@ziqianlu-desk2>
Date:   Fri, 31 Mar 2023 16:52:29 +0800
From:   Aaron Lu <aaron.lu@...el.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.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 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:

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