Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [Linuxarm] Re: [PATCH for-next 00/32] spin lock usage
 optimization for SCSI drivers
To:     Geert Uytterhoeven <geert@linux-m68k.org>
References: <1612697823-8073-1-git-send-email-tanxiaofei@huawei.com>
 <CAMuHMdXwmjq_MPr=R9twkYRoun2buuSrPDbLo6zdkGFb7XQHoQ@mail.gmail.com>
CC:     "James E.J. Bottomley" <jejb@linux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        scsi <linux-scsi@vger.kernel.org>,
        "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
        <linuxarm@openeuler.org>
From:   Xiaofei Tan <tanxiaofei@huawei.com>
Message-ID: <58053d07-ca58-2b78-36ff-40ecf162ed49@huawei.com>
Date:   Thu, 25 Feb 2021 10:37:26 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101
 Thunderbird/45.7.1
MIME-Version: 1.0
In-Reply-To: <CAMuHMdXwmjq_MPr=R9twkYRoun2buuSrPDbLo6zdkGFb7XQHoQ@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

Hi Geert,

On 2021/2/24 17:41, Geert Uytterhoeven wrote:
> Hi Xiaofei,
>
> On Sun, Feb 7, 2021 at 12:46 PM Xiaofei Tan <tanxiaofei@huawei.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?

It could only take a few CPU cycles. So there is little benefit for 
speeding up interrupt processing.You could take them as cleanup.

Is removing this cost worth the risk of introducing subtle
> regressions on platforms you cannot test yourself?
>

Currently, only found M68K platform support that high-priority interrupt 
preempts low-priority. No other platform has such services. Therefore, 
these changes do not affect non-M68K platforms.

For M68K platform, no one report such interrupt preemption case in these 
SCSI drivers.

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

Actually, no.

> Thanks for your answers!
>
> Gr{oetje,eeting}s,
>
>                         Geert
>