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

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Message-ID: <CACVXFVNuFLMOmX_KuvQG-+-zasAxcbrL+sbXEGaKa8C1K3mxKQ@mail.gmail.com>
Date:   Fri, 5 Jul 2019 09:00:58 +0800
From:   Ming Lei <tom.leiming@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.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 Mon, Jun 3, 2019 at 4:16 PM Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> 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.

Fair enough, at least difference would be made by the check in
blk_mq_make_request() if scsi_commit_rqs is provided unconditionally,
so looks fine:

Reviewed-by: Ming Lei <ming.lei@...hat.com>


Thanks,
Ming Lei