linux-kernel - Re: [PATCH] percpu_counter: increase batch count

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Date:   Thu, 18 Feb 2021 15:16:44 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] percpu_counter: increase batch count

On Thu, 18 Feb 2021 14:36:31 -0700 Jens Axboe <axboe@...nel.dk> wrote:

> Currently we cap the batch count at max(32, 2*nr_online_cpus), which these
> days is kind of silly as systems have gotten much bigger than in 2009 when
> this heuristic was introduced.
> 
> Bump it to capping it at 256 instead. This has a noticeable improvement
> for certain io_uring workloads, as io_uring tracks per-task inflight count
> using percpu counters.
> 

It will also make percpu_counter_read() and
percpu_counter_read_positive() more inaccurate than at present.  Any
effects from this will take a while to discover.

But yes, worth trying - I'll add it to the post-rc1 pile.