linux-kernel - Re: [PATCH v2] scsi: target: Save a few cycles in transport_lookup_[cmd|tmr]

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Message-ID: <b6025226-4fcd-1d82-60eb-301734cc8e5a@wanadoo.fr>
Date:   Tue, 16 Aug 2022 10:12:25 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Chaitanya Kulkarni <chaitanyak@...dia.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "michael.christie@...cle.com" <michael.christie@...cle.com>,
        "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "target-devel@...r.kernel.org" <target-devel@...r.kernel.org>,
        "Martin K. Petersen" <martin.petersen@...cle.com>
Subject: Re: [PATCH v2] scsi: target: Save a few cycles in
 transport_lookup_[cmd|tmr]_lun()


Le 16/08/2022 à 08:06, Chaitanya Kulkarni a écrit :
> On 8/15/22 13:52, Christophe JAILLET wrote:
>> Use percpu_ref_tryget_live_rcu() instead of percpu_ref_tryget_live() to
>> save a few cycles when it is known that the rcu lock is already
>> taken/released.
>>
>> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
>> ---
> do you have a quantitative data that shows actual savings of cycles?
>
> -ck
>

Some numbers were given for io_uring by the one who introduced 
percpu_ref_tryget_live_rcu().

See [1].

I don't have specific numbers for the patch against scsi.

CJ


[1]: 
https://lore.kernel.org/linux-kernel/cover.1634822969.git.asml.silence@gmail.com/