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From:   Dexuan Cui <decui@microsoft.com>
To:     "Andrea Parri (Microsoft)" <parri.andrea@gmail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>
CC:     KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Wei Liu <wei.liu@kernel.org>,
        Michael Kelley <mikelley@microsoft.com>,
        Saruhan Karademir <skarade@microsoft.com>,
        Juan Vazquez <juvazq@microsoft.com>,
        "James E.J. Bottomley" <jejb@linux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        "linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>
Subject: RE: [PATCH 1/3] scsi: storvsc: Fix max_outstanding_req_per_channel
 for Win8 and newer
Thread-Topic: [PATCH 1/3] scsi: storvsc: Fix max_outstanding_req_per_channel
 for Win8 and newer
Thread-Index: AQHW1LPvCXblZaSOtUCrOLiJZky2uan7zR/A
Date:   Thu, 17 Dec 2020 21:31:15 +0000
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References: <20201217203321.4539-1-parri.andrea@gmail.com>
 <20201217203321.4539-2-parri.andrea@gmail.com>
In-Reply-To: <20201217203321.4539-2-parri.andrea@gmail.com>
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> From: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
> Sent: Thursday, December 17, 2020 12:33 PM
>=20
> Current code overestimates the value of max_outstanding_req_per_channel
> for Win8 and newer hosts, since vmscsi_size_delta is set to the initial
> value of sizeof(vmscsi_win8_extension) rather than zero.  This may lead
> to wrong decisions when using ring_avail_percent_lowater equals to zero.
> The estimate of max_outstanding_req_per_channel is 'exact' for Win7 and
> older hosts.  A better choice, keeping the algorithm for the estimation
> simple, is to err the other way around, i.e., to underestimate for Win7
> and older but to use the exact value for Win8 and newer.
>=20
> Suggested-by: Dexuan Cui <decui@microsoft.com>
> Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
> Cc: "James E.J. Bottomley" <jejb@linux.ibm.com>
> Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
> Cc: linux-scsi@vger.kernel.org

Reviewed-by: Dexuan Cui <decui@microsoft.com>