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

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Message-ID: <f669709a-b8e6-4c76-a75c-f3e7828e09f2@xiaomi.com>
Date: Wed, 4 Sep 2024 03:35:27 +0000
From: 章辉 <zhanghui31@...omi.com>
To: Bart Van Assche <bvanassche@....org>, "axboe@...nel.dk" <axboe@...nel.dk>
CC: "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [External Mail]Re: [PATCH v3] block: move non sync requests
 complete flow to softirq

在 2024/9/4 1:28, Bart Van Assche 写道:
> [外部邮件] 
> 此邮件来源于小米公司外部，请谨慎处理。若对邮件安全性存疑，请将邮件转发给misec@...omi.com进行反馈 
>
>
> 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.
>
hi Bart,

Does set rq_affinity to 2 mean QUEUE_FLAG_SAME_COMP?

This seems to determine on which core the current request is
completed, rather than in the interrupt top or bottom half?

Thanks
Zhang