linux-kernel - RE: [PATCH] scsi: storvsc: Fix a panic in the hibernation procedure

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Message-ID: <HK0P153MB027315BB6DD813888E073664BFD20@HK0P153MB0273.APCP153.PROD.OUTLOOK.COM>
Date:   Wed, 22 Apr 2020 18:01:36 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     Ming Lei <ming.lei@...hat.com>
CC:     "Paul E. McKenney" <paulmck@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "hch@....de" <hch@....de>,
        "bvanassche@....org" <bvanassche@....org>,
        "hare@...e.de" <hare@...e.de>,
        Michael Kelley <mikelley@...rosoft.com>,
        Long Li <longli@...rosoft.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: RE: [PATCH] scsi: storvsc: Fix a panic in the hibernation procedure

> From: Ming Lei <ming.lei@...hat.com>
> Sent: Wednesday, April 22, 2020 2:24 AM
> > ...
> > storvsc_suspend() -> scsi_host_block() is only called in the hibernation
> > path, which is not a hot path at all, so IMHO we don't really care if it
> > takes 10ms or 100ms or even 1s. :-)  BTW, in my test, typically the
> 
> Are you sure the 'we' can cover all users?

I actully only meant I don't have any performance concern in this path
storvsc_suspend() -> scsi_host_block()  :-)

Thanks for your effort to improve the scsi_host_block() API in the patch
[PATCH] scsi: avoid to run synchronize_rcu for each device in scsi_host_block.
 
> > scsi_host_block() here takes about 3ms in my 40-vCPU VM.
> 
> If more LUNs are added, the time should be increased proportionallly,
> that is why I think scsi_host_block() is bad.
> 
> Thanks,
> Ming

FWIW, if the time increases linearly against the number of the LUNs, it
looks typically it's still fast enough for storvsc_suspend().

Thanks,
-- Dexuan