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SDHCI changed from using a tasklet to finish requests, to using an IRQ thread i.e. commitc07a48c265("mmc: sdhci: Remove finish_tasklet"). Because this increased the latency to complete requests, a preparatory change was made to complete the request from the IRQ handler if possible i.e. commit19d2f695f4("mmc: sdhci: Call mmc_request_done() from IRQ handler if possible"). That alleviated the situation for MMC block devices because the MMC block driver makes use of mmc_pre_req() and mmc_post_req() so that successful requests are completed in the IRQ handler and any DMA unmapping is handled separately in mmc_post_req(). However SDIO was still affected, and an example has been reported with up to 20% degradation in performance. Looking at SDIO I/O helper functions, sdio_io_rw_ext_helper() appeared to be a possible candidate for making use of asynchronous requests within its I/O loops, but analysis revealed that these loops almost never iterate more than once, so the complexity of the change would not be warrented. Instead, mmc_pre_req() and mmc_post_req() are added before and after I/O submission (mmc_wait_for_req) in mmc_io_rw_extended(). This still has the potential benefit of reducing the duration of interrupt handlers, as well as addressing the latency issue for SDHCI. It also seems a more reasonable solution than forcing drivers to do everything in the IRQ handler. Reported-by: Dmitry Osipenko <digetx@gmail.com> Fixes:c07a48c265("mmc: sdhci: Remove finish_tasklet") Signed-off-by: Adrian Hunter <adrian.hunter@intel.com> Tested-by: Dmitry Osipenko <digetx@gmail.com> Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20200903082007.18715-1-adrian.hunter@intel.com Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.