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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <134fc34c-10b8-4d00-aaca-8285efce9899@redhat.com>
Date: Wed, 17 Jul 2024 14:18:39 -0400
From: Waiman Long <longman@...hat.com>
To: "tj@...nel.org" <tj@...nel.org>
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


On 7/17/24 13:40, tj@...nel.org wrote:
> 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?

Well, it can be confusing whether we are dealing with blkg->iostat or 
blkg->iostat_cpu. In many cases, we are dealing with iostat_cpu instead 
of iostat like __blkcg_rstat_flush() and blkg_clear_stat(). So we can't 
eliminate the use of u64_stats_update_begin_irqsave() in those cases.

Cheers,
Longman