linux-kernel - Re: [PATCH 2/4] mmc: Add virtual command queue support

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Date:   Tue, 10 Sep 2019 11:27:09 +0800
From:   Baolin Wang <baolin.wang@...aro.org>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>, asutoshd@...eaurora.org,
        Orson Zhai <orsonzhai@...il.com>,
        Chunyan Zhang <zhang.lyra@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/4] mmc: Add virtual command queue support

On Mon, 9 Sep 2019 at 20:45, Adrian Hunter <adrian.hunter@...el.com> wrote:
>
> On 9/09/19 3:16 PM, Baolin Wang wrote:
> > Hi Adrian,
> >
> > On Mon, 9 Sep 2019 at 20:02, Adrian Hunter <adrian.hunter@...el.com> wrote:
> >>
> >> On 6/09/19 6:52 AM, Baolin Wang wrote:
> >>> Now the MMC read/write stack will always wait for previous request is
> >>> completed by mmc_blk_rw_wait(), before sending a new request to hardware,
> >>> or queue a work to complete request, that will bring context switching
> >>> overhead, especially for high I/O per second rates, to affect the IO
> >>> performance.
> >>>
> >>> Thus this patch introduces virtual command queue interface, which is
> >>> similar with the hardware command queue engine's idea, that can remove
> >>> the context switching.
> >>
> >> CQHCI is a hardware interface for eMMC's that support command queuing.  What
> >> you are doing is a software issue queue, unrelated to CQHCI.  I think you
> >
> > Yes.
> >
> >> should avoid all reference to CQHCI i.e. call it something else.
> >
> > Since its process is similar with CQHCI and re-use the CQHCI's
> > interfaces, I called it virtual command queue. I am not sure what else
> > name is better, any thoughts? VCQHCI? Thanks.
>
> What about swq for software queue.  Maybe Ulf can suggest something?

Um, though changing to use swq, still need reuse command queue's
interfaces, like 'mq->use-cqe', 'host->cqe_depth' and cqe ops and so
on, looks a little weird for me. But if you all agree with this name,
then I am okay. Ulf, what do you suggest?

-- 
Baolin Wang
Best Regards