linux-kernel - Re: [PATCH v3] block: move non sync requests complete flow to softirq

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Message-ID: <769fb0e4-6f55-4a2d-a0f2-e8836b790617@acm.org>
Date: Tue, 3 Sep 2024 10:28:32 -0700
From: Bart Van Assche <bvanassche@....org>
To: ZhangHui <zhanghui31@...omi.com>, axboe@...nel.dk
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] block: move non sync requests complete flow to softirq

On 9/3/24 4:54 AM, ZhangHui wrote:
> Currently, for a controller that supports multiple queues, like UFS4.0,
> the mq_ops->complete is executed in the interrupt top-half. Therefore,
> the file system's end io is executed during the request completion process,
> such as f2fs_write_end_io on smartphone.
> 
> However, we found that the execution time of the file system end io
> is strongly related to the size of the bio and the processing speed
> of the CPU. Because the file system's end io will traverse every page
> in bio, this is a very time-consuming operation.
> 
> We measured that the 80M bio write operation on the little CPU will
> cause the execution time of the top-half to be greater than 100ms.
> The CPU tick on a smartphone is only 4ms, which will undoubtedly affect
> scheduling efficiency.
> 
> Let's fixed this issue by moved non sync request completion flow to
> softirq, and keep the sync request completion in the top-half.

An explanation is missing from the patch description why this issue
cannot be solved by changing rq_affinity to 2.

Thanks,

Bart.