linux-kernel - Re: [PATCH -next RFC 2/6] block: refactor to split bio thoroughly

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Message-ID: <338207c2-e3cd-abc1-6b8c-f08645ef144a@kernel.dk>
Date:   Tue, 29 Mar 2022 08:41:57 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Yu Kuai <yukuai3@...wei.com>, andriy.shevchenko@...ux.intel.com,
        john.garry@...wei.com, ming.lei@...hat.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        yi.zhang@...wei.com
Subject: Re: [PATCH -next RFC 2/6] block: refactor to split bio thoroughly

On 3/29/22 8:40 AM, Christoph Hellwig wrote:
> On Tue, Mar 29, 2022 at 08:35:29AM -0600, Jens Axboe wrote:
>>> But more importantly why does your use case even have splits that get
>>> submitted together?  Is this a case of Linus' stupidly low default
>>> max_sectors when the hardware supports more, or is the hardware limited
>>> to a low number of sectors per request?  Or do we hit another reason
>>> for the split?
>>
>> See the posted use case, it's running 512kb ios on a 128kb device.
> 
> That is an awfully low limit these days.  I'm really not sure we should
> optimize the block layer for that.

That's exactly what my replies have been saying. I don't think this is
a relevant thing to optimize for.

Fixing fairness for wakeups seems useful, however.

-- 
Jens Axboe