linux-kernel - Re: [PATCH 1/2] scsi_host: add support for request batching

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Message-ID: <bd7fa062-6c71-13a2-5bbf-0dea859ae75f@redhat.com>
Date:   Mon, 3 Jun 2019 10:16:21 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Ming Lei <tom.leiming@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        KVM General <kvm@...r.kernel.org>, jejb@...ux.ibm.com,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Linux SCSI List <linux-scsi@...r.kernel.org>,
        Stefan Hajnoczi <stefanha@...hat.com>
Subject: Re: [PATCH 1/2] scsi_host: add support for request batching

On 31/05/19 05:27, Ming Lei wrote:
> It should be fine to implement scsi_commit_rqs() as:
> 
>  if (shost->hostt->commit_rqs)
>        shost->hostt->commit_rqs(shost, hctx->queue_num);
> 
> then scsi_mq_ops_no_commit can be saved.
> 
> Because .commit_rqs() is only called when BLK_STS_*_RESOURCE is
> returned from scsi_queue_rq(), at that time shost->hostt->commit_rqs should
> have been hit from cache given .queuecommand is called via
> host->hostt->queuecommand.

This is not about d-cache, it's about preserving the heuristics that
blk-mq applies depending on whether commit_rqs is there or not.

Paolo