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From: "Yu Kuai" <yukuai@fnnas.com>
To: "Doug Smythies" <dsmythies@telus.net>
Cc: "'Nilay Shroff'" <nilay@linux.ibm.com>,
	 "'Bart Van Assche'" <bvanassche@acm.org>,
	 "'Jens Axboe'" <axboe@kernel.dk>, <linux-kernel@vger.kernel.org>,
	 <yukuai@fnnas.com>
Subject: Re: REGRESSION BISECTED: mq-deadline: covert to use request_queue->async_depth
Date: Sat, 11 Apr 2026 00:21:04 +0800	[thread overview]
Message-ID: <6e336fc5-bf39-41eb-a499-6728969bf164@fnnas.com> (raw)
In-Reply-To: <004b01dcc8a9$7d6ac610$78405230$@telus.net>

Hi,

在 2026/4/10 13:18, Doug Smythies 写道:
>> Do you ever use the async_depth for mq-deadline?
> No.

Then the only difference is the tag wake batch is changed from 1 to 8. However,
batch wake up is the base design of sbitmap. And I do admit tail latency is
bad under high concurrency is probably due to wake up is unfair, this is a
know sbitmap design flaw and not fixed yet.

You could try change wake up batch back to 1. However, I don't think this is a
good solution. And I'll suggest you to try increase nr_requests to see if tail
latency gets better.

Per

-- 
Thansk,
Kuai

  reply	other threads:[~2026-04-10 16:21 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-04-08 23:20 Doug Smythies
2026-04-09 12:34 ` Yu Kuai
2026-04-10  5:18   ` Doug Smythies
2026-04-10 16:21     ` Yu Kuai [this message]
2026-04-14  3:21       ` Doug Smythies

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