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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Wed, 27 Nov 2019 13:01:06 +0100
Message-ID: <CAK8P3a0gUWf_+ZmscuFanvPG=wN09ELL-JpByjJJM4Lo1FYmrQ@mail.gmail.com>
Subject: Re: [PATCH v6 0/4] Add MMC software queue support
To:     Christoph Hellwig <hch@infradead.org>
Cc:     Hannes Reinecke <hare@suse.de>,
        "(Exiting) Baolin Wang" <baolin.wang@linaro.org>,
        Baolin Wang <baolin.wang7@gmail.com>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Ulf Hansson <ulf.hansson@linaro.org>,
        Asutosh Das <asutoshd@codeaurora.org>,
        Orson Zhai <orsonzhai@gmail.com>,
        Lyra Zhang <zhang.lyra@gmail.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        linux-mmc <linux-mmc@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Hannes Reinecke <hare@suse.com>,
        linux-block <linux-block@vger.kernel.org>,
        Paolo Valente <paolo.valente@linaro.org>
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On Wed, Nov 27, 2019 at 10:00 AM Christoph Hellwig <hch@infradead.org> wrote:
>
> On Tue, Nov 26, 2019 at 12:17:15PM +0100, Hannes Reinecke wrote:
>  If requests are batched enough we could just drain
> and switch every time an other partition access comes in.  Especially
> so if people only use partitions for boot partitions and other rarely
> used areas.

We only support a single user partition plus up to two boot partitions that
are accessed rarely, I don't think there is any reason to optimize switching
between them.

The only change that I think we need here is to change the partition switch
from something that is done synchronously during ->queue_rq() to
something that fits better into normal scheme of sending a cmd to
the device, returning BLK_STS_RESOURCE from ->queue_rq.
Possibly this could even be turned into a standard struct request that is
added between two normal requests for different partitions at some
point, if this simplifies the logic (I suspect it won't, but it may be worth
a try).

      Arnd