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Date:   Mon, 2 Mar 2020 14:15:41 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     John Garry <john.garry@huawei.com>
Cc:     Ming Lei <ming.lei@redhat.com>,
        James Bottomley <James.Bottomley@HansenPartnership.com>,
        linux-scsi@vger.kernel.org,
        "Martin K . Petersen" <martin.petersen@oracle.com>,
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        "Ewan D . Milne" <emilne@redhat.com>,
        Hannes Reinecke <hare@suse.de>,
        Bart Van Assche <bart.vanassche@wdc.com>,
        Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH] scsi: avoid to fetch scsi host template instance in IO
 path
Message-ID: <20200302131541.GA13265@lst.de>
References: <20200228093346.31213-1-ming.lei@redhat.com> <f23daab7-7aa0-1c34-8137-7abead09016c@huawei.com>
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On Mon, Mar 02, 2020 at 10:58:55AM +0000, John Garry wrote:
> On 28/02/2020 09:33, Ming Lei wrote:
>> scsi host template struct is quite big, and the following three
>> fields are needed in SCSI IO path:
>>
>> - queuecommand
>> - commit_rqs
>> - cmd_size
>
> Would it have been nearly as good to reorganise Scsi host template 
> structure to ensure that these are adjacent?
>
> I say nearly, as it avoids the shost->hostt read.

That would be worth trying.  Replicating function pointers out of
read-only data structures generally isn't a very good idea.