linux-kernel - Re: [PATCH 00/11] md: avoid counter operation conflicts

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Date: Wed, 10 Apr 2024 14:13:50 -0700
From: Song Liu <song@...nel.org>
To: tada keisuke <keisuke1.tada@...xia.com>
Cc: "yukuai3@...wei.com" <yukuai3@...wei.com>, 
	"linux-raid@...r.kernel.org" <linux-raid@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 00/11] md: avoid counter operation conflicts

Thanks for the patchset!

On Tue, Mar 26, 2024 at 3:29 AM tada keisuke <keisuke1.tada@...xia.com> wrote:
>
> Currently, active_aligned_reads and nr_pending used as counters are atomic types.
> Therefore, when inc/dec in a multi-core results in conflicts.
>
> To solve this problem, use "percpu_ref" counters that can avoid conflicts and maintain consistency.
>
> Switch modes of percpu_ref to achieve both consistency and conflict avoidance.
> During normal operations such as inc/dec, it operates as percpu mode.
> When consistency is required, it operates as atomic mode.
> The operations that require consistency are as follows:
> ・Zero check for the counter
> ・All operations in RAID 1/10

IIUC, the patchset is to resolve race conditions and thus improve performance.
If this is the case, could you please include some performance numbers in the
next version?

Thanks,
Song