linux-kernel - Re: [PATCH] nvmet: use try_cmpxchg in nvmet_update_sq

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Message-ID: <220dabe6-dac1-8ca7-0134-e6e89c923d81@nvidia.com>
Date:   Tue, 25 Oct 2022 00:47:05 +0000
From:   Chaitanya Kulkarni <chaitanyak@...dia.com>
To:     Uros Bizjak <ubizjak@...il.com>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Christoph Hellwig <hch@....de>, Sagi Grimberg <sagi@...mberg.me>,
        Chaitanya Kulkarni <chaitanyak@...dia.com>
Subject: Re: [PATCH] nvmet: use try_cmpxchg in nvmet_update_sq_head

On 10/20/22 08:35, Uros Bizjak wrote:
> Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in
> nvmet_update_sq_head.  x86 CMPXCHG instruction returns success in ZF flag, so
> this change saves a compare after cmpxchg (and related move instruction in
> front of cmpxchg).
> 

Is it worth a share delts of assembly instructions of the changes above?
as developers on block mailing list are sharing the delta between before
and after patch including the assembly.

I also hope that you have tested this change with blktests nvme.

Either way:-

Reviewed-by: ChaItanya Kulkarni <kch@...dia.com>

-ck