linux-kernel - Re: [PATCH for-next 00/32] spin lock usage optimization for SCSI drivers

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Date:   Wed, 24 Feb 2021 10:41:19 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Xiaofei Tan <tanxiaofei@...wei.com>
Cc:     "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        scsi <linux-scsi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linuxarm@...neuler.org
Subject: Re: [PATCH for-next 00/32] spin lock usage optimization for SCSI drivers

Hi Xiaofei,

On Sun, Feb 7, 2021 at 12:46 PM Xiaofei Tan <tanxiaofei@...wei.com> wrote:
> Replace spin_lock_irqsave with spin_lock in hard IRQ of SCSI drivers.
> There are no function changes, but may speed up if interrupt happen
> too often.

I'll bite: how much does this speed up interrupt processing?
What's the typical cost of saving/disabling, and restoring interrupt
state?  Is removing this cost worth the risk of introducing subtle
regressions on platforms you cannot test yourself?

BTW, how many of these legacy SCSI controllers do you have access to?

Thanks for your answers!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds