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

[Jens Axboe <axboe@kernel.dk>]

On 9/3/24 11:28 AM, Bart Van Assche wrote:
> 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.

And what's also missing is a changelog - to the poster, always include
what's changed since the last version posted. Otherwise you just have
3 random patches posted and leave the discovery of why on earth there's
now a v3 to the reader in having to pull in all 3 versions and see if
the progression made sense.

-- 
Jens Axboe