linux-kernel - Re: [PATCH] blk-mq: Use request queue-wide tags for tagset-wide sbitmap

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Date:   Tue, 11 May 2021 08:33:18 +0100
From:   John Garry <john.garry@...wei.com>
To:     Ming Lei <ming.lei@...hat.com>
CC:     <axboe@...nel.dk>, <linux-block@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-scsi@...r.kernel.org>,
        <kashyap.desai@...adcom.com>, <chenxiang66@...ilicon.com>,
        <yama@...hat.com>, Douglas Gilbert <dgilbert@...erlog.com>
Subject: Re: [PATCH] blk-mq: Use request queue-wide tags for tagset-wide
 sbitmap

On 11/05/2021 01:52, Ming Lei wrote:
>> fixed.
>>
>> Ming and Yanhui report higher CPU usage and lower throughput in scenarios
>> where the fixed total driver tag depth is appreciably lower than the total
>> scheduler tag depth:
>> https://lore.kernel.org/linux-block/440dfcfc-1a2c-bd98-1161-cec4d78c6dfc@huawei.com/T/#mc0d6d4f95275a2743d1c8c3e4dc9ff6c9aa3a76b
>>
> No difference any more wrt. fio running on scsi_debug with this patch in
> Yanhui's test machine:
> 
> 	modprobe scsi_debug host_max_queue=128 submit_queues=32 virtual_gb=256 delay=1
> vs.
> 	modprobe scsi_debug max_queue=128 submit_queues=1 virtual_gb=256 delay=1
> 
> Without this patch, the latter's result is 30% higher than the former's.
> 

ok, good. I'll post a v2 with comments addressed.

> note: scsi_debug's queue depth needs to be updated to 128 for avoiding io hang,
> which is another scsi issue.
> 
I was just carrying Doug's patch to test.

Thanks,
John