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Message-ID: <2562353d-bfe3-a2b1-5427-76426cbda7b4@huaweicloud.com>
Date: Sat, 14 Dec 2024 10:44:31 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Bart Van Assche <bvanassche@....org>, Yu Kuai <yukuai1@...weicloud.com>,
 axboe@...nel.dk, akpm@...ux-foundation.org, yang.yang@...o.com,
 ming.lei@...hat.com, osandov@...com, paolo.valente@...aro.org
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
 yi.zhang@...wei.com, yangerkun@...wei.com, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH RFC 1/3] block/mq-deadline: Revert "block/mq-deadline: Fix
 the tag reservation code"

Hi, Bart

在 2024/12/11 4:33, Bart Van Assche 写道:
>> If so, following are the options that I can think of to fix this:
>>
>> 1) make async_depth read-only, if 75% tags will hurt performance in some
>> cases, user can increase nr_requests to prevent it.
>> 2) refactor elevator sysfs api, remove eq->sysfs_lock and replace it
>> with q->sysfs_lock, so deadline_async_depth_store() will be protected
>> against changing hctxs, and min_shallow_depth can be updated here.
>> 3) other options?
> 
> Another option is to remove the ability to configure async_depth. If it
> is too much trouble to get the implementation right without causing
> regressions for existing workloads, one possibility is to remove support
> for restricting the number of asynchronous requests in flight.

If you agree, I'll use following option in the next version:

4) set min_async_depth to 64 (after treating min_shallow_depth for the
whole sbitmap instead of one word).

The good thing is that user can still set async_depth without changing
wake_batch, the side effect is that async_depth can't be used if
nr_requests <= 64;

Thanks,
Kuai


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