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Subject: Re: [PATCH V2 00/20] blk-mq-sched: improve SCSI-MQ performance
From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Christoph Hellwig <hch@infradead.org>,
        Ming Lei <ming.lei@redhat.com>
Cc: Jens Axboe <axboe@fb.com>, linux-block@vger.kernel.org,
        Bart Van Assche <bart.vanassche@sandisk.com>,
        Laurence Oberman <loberman@redhat.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        linux-scsi@vger.kernel.org
Date: Fri, 11 Aug 2017 07:25:50 -0700
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On Fri, 2017-08-11 at 01:11 -0700, Christoph Hellwig wrote:
> [+ Martin and linux-scsi]
> 
> Given that we need this big pile and a few bfq fixes to avoid
> major regressesions I'm tempted to revert the default to scsi-mq
> for 4.14, but bring it back a little later for 4.15.
> 
> What do you think?  Maybe for 4.15 we could also do it through the
> block tree where all the fixes will be queued.

Given the severe workload regressions Mel reported, I think that's
wise.

I also think we wouldn't have found all these problems if it hadn't
been the default, so the original patch was the best way of trying to
find out if we were ready for the switch and forcing all the issues
out.

Thanks,

James