linux-kernel - Re: [PATCH 0/2] block/SCSI MQ: two RESTART related patches

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Date:   Tue, 17 Oct 2017 16:47:23 +0100
From:   John Garry <john.garry@...wei.com>
To:     Ming Lei <ming.lei@...hat.com>, Jens Axboe <axboe@...com>,
        <linux-block@...r.kernel.org>,
        Christoph Hellwig <hch@...radead.org>
CC:     Bart Van Assche <bart.vanassche@...disk.com>,
        <linux-kernel@...r.kernel.org>, <linux-scsi@...r.kernel.org>,
        Omar Sandoval <osandov@...com>, Linuxarm <linuxarm@...wei.com>
Subject: Re: [PATCH 0/2] block/SCSI MQ: two RESTART related patches

On 17/10/2017 06:12, Ming Lei wrote:
> On Tue, Oct 17, 2017 at 01:04:16PM +0800, Ming Lei wrote:
>> Hi Jens,
>>
>> The 1st patch runs idle hctx after dealy in scsi_mq_get_budget(),
>> so that we can keep same behaviour with before, and it can be
>> thought as a fix.
>>
>> The 2nd patch cleans up RESTART, and removes handling for TAG_SHARED
>> from current blk-mq's RESTART mechanism because SCSI_MQ can covers its
>> restart by itself, so that no need to handle TAG_SHARED in blk-mq
>> RESTART. And >20% IOPS boost is observed in my rand read test over
>> scsi_debug.
>>
>> John, please test this two patches and see if it may improve your SAS
>> IO performance, and you can find the two patches in the following branch:
>>
>> 	https://github.com/ming1/linux/commits/blk_mq_improve_restart_V1
>

Hi Ming,

As requested, here's my figures for blk_mq_improve_restart_V1:
without default SCSI_MQ, deadline scheduler, CONFIG PREEMPT off
read, rw, write IOPS	
989K, 113K/113K, 835K

with default SCSI_MQ, mq-deadline scheduler, CONFIG PREEMPT off
read, rw, write IOPS	
738K, 130K/130K, 686K

For axboe for-next tip (21ed538):
without default SCSI_MQ, deadline scheduler, CONFIG PREEMPT off
read, rw, write IOPS	
977K, 117K/117K, 821K

with default SCSI_MQ, mq-deadline scheduler, CONFIG PREEMPT off
read, rw, write IOPS	
733K, 128K/128K, 676K

All cases do not have LLDD mq exposed/enabled. So unfortunately not much 
difference with your branch.

cheers,
John

> Forget to mention, you need to either pull the above branch directly
> or apply the two patches against for-next branch of Jens' block
> tree:
>
> 	git://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git #for-next
>