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From:   Dexuan Cui <decui@microsoft.com>
To:     Ming Lei <ming.lei@redhat.com>
CC:     "Paul E. McKenney" <paulmck@kernel.org>,
        Josh Triplett <josh@joshtriplett.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
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        Michael Kelley <mikelley@microsoft.com>,
        Long Li <longli@microsoft.com>,
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        "wei.liu@kernel.org" <wei.liu@kernel.org>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        KY Srinivasan <kys@microsoft.com>,
        "linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>
Subject: RE: [PATCH] scsi: storvsc: Fix a panic in the hibernation procedure
Thread-Topic: [PATCH] scsi: storvsc: Fix a panic in the hibernation procedure
Thread-Index: AQHWGEVb6DFeJK2tFE2eFTHRpRyDH6iEXZcAgAArmvCAAAOn4IAAUhWAgACLYPA=
Date:   Wed, 22 Apr 2020 18:01:36 +0000
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> From: Ming Lei <ming.lei@redhat.com>
> Sent: Wednesday, April 22, 2020 2:24 AM
> > ...
> > storvsc_suspend() -> scsi_host_block() is only called in the hibernatio=
n
> > path, which is not a hot path at all, so IMHO we don't really care if i=
t
> > takes 10ms or 100ms or even 1s. :-)  BTW, in my test, typically the
>=20
> 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_blo=
ck.
=20
> > scsi_host_block() here takes about 3ms in my 40-vCPU VM.
>=20
> If more LUNs are added, the time should be increased proportionallly,
> that is why I think scsi_host_block() is bad.
>=20
> 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