Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra scheduler

From	Mark Brown <broonie@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra scheduler
Date	2016-10-28 19:20 +0200
Message-ID	<sxiYW-2LI-13@gated-at.bofh.it> (permalink)
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On Fri, Oct 28, 2016 at 06:05:35PM +0200, Arnd Bergmann wrote:
> On Friday, October 28, 2016 9:30:07 AM CEST Jens Axboe wrote:

> > Also, 4.8 and newer have support for BLK_MQ_F_BLOCKING, if you need to
> > block in ->queue_rq(). That could eliminate the need to offload to a
> > kthread manually.

> I think the main reason for the kthread is that on ARM and other
> architectures, the dma mapping operations are fairly slow (for
> cache flushes or bounce buffering) and we want to minimize the
> time between subsequent requests being handled by the hardware.

> This is not unique to MMC in any way, MMC just happens to be
> common on ARM and it is limited by its lack of hardware
> command queuing.

Plus the fact that MMC (and SD) have some *relatively* high performance
implementations which amplify the effects of desaturating the hardware -
the faster the hardware is the more noticable the overhead of stalling
it becomes.

Thread

Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra scheduler Ulf Hansson <ulf.hansson@linaro.org> - 2016-10-27 19:40 +0200
  Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra  scheduler Jens Axboe <axboe@kernel.dk> - 2016-10-27 19:50 +0200
    Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra scheduler Ulf Hansson <ulf.hansson@linaro.org> - 2016-10-27 20:20 +0200
      Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra  scheduler Jens Axboe <axboe@kernel.dk> - 2016-10-27 20:30 +0200
        Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra scheduler Ulf Hansson <ulf.hansson@linaro.org> - 2016-10-27 21:40 +0200
          Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra  scheduler Jens Axboe <axboe@kernel.dk> - 2016-10-27 23:10 +0200
            Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra scheduler Linus Walleij <linus.walleij@linaro.org> - 2016-10-28 00:30 +0200
              Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra scheduler Linus Walleij <linus.walleij@linaro.org> - 2016-10-28 11:40 +0200
                Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra  scheduler Jens Axboe <axboe@kernel.dk> - 2016-10-28 16:30 +0200
                Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra scheduler Linus Walleij <linus.walleij@linaro.org> - 2016-10-28 22:40 +0200
                Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra  scheduler Christoph Hellwig <hch@infradead.org> - 2016-10-28 17:30 +0200
                Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra scheduler Linus Walleij <linus.walleij@linaro.org> - 2016-10-28 23:10 +0200
                Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra  scheduler Jens Axboe <axboe@kernel.dk> - 2016-10-28 17:40 +0200
                Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra  scheduler Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> - 2016-10-28 18:00 +0200
                Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra scheduler Arnd Bergmann <arnd@arndb.de> - 2016-10-28 18:10 +0200
                Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra  scheduler Mark Brown <broonie@kernel.org> - 2016-10-28 19:20 +0200
              Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra  scheduler Jens Axboe <axboe@kernel.dk> - 2016-10-28 16:10 +0200
            Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra scheduler Ulf Hansson <ulf.hansson@linaro.org> - 2016-10-28 08:40 +0200
              Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra  scheduler Jens Axboe <axboe@kernel.dk> - 2016-10-28 16:20 +0200
                Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra  scheduler Mark Brown <broonie@kernel.org> - 2016-10-28 19:20 +0200
        Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra  scheduler Christoph Hellwig <hch@infradead.org> - 2016-10-27 21:50 +0200
          Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra  scheduler Mark Brown <broonie@kernel.org> - 2016-10-28 00:10 +0200
        Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra  scheduler Mark Brown <broonie@kernel.org> - 2016-10-27 21:50 +0200
      Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra scheduler Arnd Bergmann <arnd@arndb.de> - 2016-10-28 14:10 +0200
        Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra scheduler Richard Weinberger <richard.weinberger@gmail.com> - 2016-10-28 14:20 +0200

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