linux-kernel - Re: [PATCH v3] blk-cgroup: Replace u64 sync with spinlock for iostat update

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Message-ID: <ZpgB9kCAxAAXAtSi@slm.duckdns.org>
Date: Wed, 17 Jul 2024 07:40:06 -1000
From: "tj@...nel.org" <tj@...nel.org>
To: Waiman Long <longman@...hat.com>
Cc: Boy Wu (吳勃誼) <Boy.Wu@...iatek.com>,
	"boris@....io" <boris@....io>,
	"linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
	"linux-mediatek@...ts.infradead.org" <linux-mediatek@...ts.infradead.org>,
	"axboe@...nel.dk" <axboe@...nel.dk>,
	Iverlin Wang (王苳霖) <Iverlin.Wang@...iatek.com>,
	"josef@...icpanda.com" <josef@...icpanda.com>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"matthias.bgg@...il.com" <matthias.bgg@...il.com>,
	"angelogioacchino.delregno@...labora.com" <angelogioacchino.delregno@...labora.com>
Subject: Re: [PATCH v3] blk-cgroup: Replace u64 sync with spinlock for iostat
 update

Hello, Waiman.

On Wed, Jul 17, 2024 at 01:37:56PM -0400, Waiman Long wrote:
> bis->sync is still being used in blk_cgroup_bio_start(). Replacing it with a
> global lock may kill performance. We may have to use a per-cpu lock if we
> want to go this route of eliminating bis->sync.

So, the idea is to keep using u64_sync for blkg->iostat_cpu and use
blkg_stat_lock for blkg->iostat. The former is the only one which is updated
in hot path, right?

Thanks.

-- 
tejun