linux-kernel - Re: [PATCH v8 17/18] scsi: megaraid_sas: Added support for shared host tagset for cpuhotplug

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Date:   Mon, 02 Nov 2020 10:24:59 -0500
From:   Qian Cai <cai@...hat.com>
To:     Kashyap Desai <kashyap.desai@...adcom.com>,
        John Garry <john.garry@...wei.com>, axboe@...nel.dk,
        jejb@...ux.ibm.com, martin.petersen@...cle.com,
        don.brace@...rosemi.com, ming.lei@...hat.com, bvanassche@....org,
        dgilbert@...erlog.com, paolo.valente@...aro.org, hare@...e.de,
        hch@....de
Cc:     Sumit Saxena <sumit.saxena@...adcom.com>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-scsi@...r.kernel.org, esc.storagedev@...rosemi.com,
        "PDL,MEGARAIDLINUX" <megaraidlinux.pdl@...adcom.com>,
        chenxiang66@...ilicon.com, luojiaxing@...wei.com,
        Hannes Reinecke <hare@...e.com>
Subject: Re: [PATCH v8 17/18] scsi: megaraid_sas: Added support for shared
 host tagset for cpuhotplug

On Mon, 2020-11-02 at 20:01 +0530, Kashyap Desai wrote:
> > On Wed, 2020-08-19 at 23:20 +0800, John Garry wrote:
> > > From: Kashyap Desai <kashyap.desai@...adcom.com>
> > > 
> > > Fusion adapters can steer completions to individual queues, and we now
> > > have support for shared host-wide tags.
> > > So we can enable multiqueue support for fusion adapters.
> > > 
> > > Once driver enable shared host-wide tags, cpu hotplug feature is also
> > > supported as it was enabled using below patchsets - commit
> > > bf0beec0607d ("blk-mq: drain I/O when all CPUs in a hctx are
> > > offline")
> > > 
> > > Currently driver has provision to disable host-wide tags using
> > > "host_tagset_enable" module parameter.
> > > 
> > > Once we do not have any major performance regression using host-wide
> > > tags, we will drop the hand-crafted interrupt affinity settings.
> > > 
> > > Performance is also meeting the expecatation - (used both none and
> > > mq-deadline scheduler)
> > > 24 Drive SSD on Aero with/without this patch can get 3.1M IOPs
> > > 3 VDs consist of 8 SAS SSD on Aero with/without this patch can get
> > > 3.1M IOPs.
> > > 
> > > Signed-off-by: Kashyap Desai <kashyap.desai@...adcom.com>
> > > Signed-off-by: Hannes Reinecke <hare@...e.com>
> > > Signed-off-by: John Garry <john.garry@...wei.com>
> > 
> > Reverting this commit fixed an issue that Dell Power Edge R6415 server
> > with
> > megaraid_sas is unable to boot.
> 
> I will take a look at this. BTW, can you try keeping same PATCH but use
> module parameter "host_tagset_enable =0"

Yes, that also works.