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

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Date:   Mon, 9 Sep 2019 15:01:32 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Baolin Wang <baolin.wang@...aro.org>, ulf.hansson@...aro.org,
        riteshh@...eaurora.org, asutoshd@...eaurora.org
Cc:     orsonzhai@...il.com, zhang.lyra@...il.com, arnd@...db.de,
        linus.walleij@...aro.org, vincent.guittot@...aro.org,
        linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] mmc: Add virtual command queue support

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
should avoid all reference to CQHCI i.e. call it something else.