linux-kernel - Re: [RFC PATCH] driver: loop: introduce synchronized read for loop driver

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Message-ID: <aNGQ66CD9F82BFP-@infradead.org>
Date: Mon, 22 Sep 2025 11:09:47 -0700
From: Christoph Hellwig <hch@...radead.org>
To: "zhaoyang.huang" <zhaoyang.huang@...soc.com>
Cc: Jens Axboe <axboe@...nel.dk>, Ming Lei <ming.lei@...hat.com>,
	linux-mm@...ck.org, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Zhaoyang Huang <huangzhaoyang@...il.com>, steve.kang@...soc.com
Subject: Re: [RFC PATCH] driver: loop: introduce synchronized read for loop
 driver

On Mon, Sep 22, 2025 at 11:29:15AM +0800, zhaoyang.huang wrote:
> From: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> 
> For now, my android system with per pid memcgv2 setup are suffering
> high block_rq_issue to block_rq_complete latency which is actually
> introduced by schedule latency of too many kworker threads. By further
> investigation, we found that the EAS scheduler which will pack small
> load tasks into one CPU core will make this scenario worse. This commit
> would like to introduce a way of synchronized read to be helpful on
> this scenario. The I2C of loop device's request reduced from 14ms to
> 2.1ms under fio test.

So fix the scheduler, or create less helper threads, but this work
around really look like fixing the symptoms instead of even trying
to aim for the root cause.