On Thu, 3 Sep 2020 at 10:20, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:
>
> SDHCI changed from using a tasklet to finish requests, to using an IRQ
> thread i.e. commit c07a48c2651965 ("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. commit 19d2f695f4e827 ("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.
Briljant!
So, this should mean that other host drivers that use threaded IRQ
handlers could benefit as well. It would certainly be interesting to
hear from other tests about this.
>
> Reported-by: Dmitry Osipenko <digetx@xxxxxxxxx>
> Fixes: c07a48c2651965 ("mmc: sdhci: Remove finish_tasklet")
> Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> Tested-by: Dmitry Osipenko <digetx@xxxxxxxxx>
Applied for fixes and by adding a stable tag, thanks!
Kind regards
Uffe
> ---
> drivers/mmc/core/sdio_ops.c | 39 +++++++++++++++++++++----------------
> 1 file changed, 22 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/mmc/core/sdio_ops.c b/drivers/mmc/core/sdio_ops.c
> index 93d346c01110..4c229dd2b6e5 100644
> --- a/drivers/mmc/core/sdio_ops.c
> +++ b/drivers/mmc/core/sdio_ops.c
> @@ -121,6 +121,7 @@ int mmc_io_rw_extended(struct mmc_card *card, int write, unsigned fn,
> struct sg_table sgtable;
> unsigned int nents, left_size, i;
> unsigned int seg_size = card->host->max_seg_size;
> + int err;
>
> WARN_ON(blksz == 0);
>
> @@ -170,28 +171,32 @@ int mmc_io_rw_extended(struct mmc_card *card, int write, unsigned fn,
>
> mmc_set_data_timeout(&data, card);
>
> - mmc_wait_for_req(card->host, &mrq);
> + mmc_pre_req(card->host, &mrq);
>
> - if (nents > 1)
> - sg_free_table(&sgtable);
> + mmc_wait_for_req(card->host, &mrq);
>
> if (cmd.error)
> - return cmd.error;
> - if (data.error)
> - return data.error;
> -
> - if (mmc_host_is_spi(card->host)) {
> + err = cmd.error;
> + else if (data.error)
> + err = data.error;
> + else if (mmc_host_is_spi(card->host))
> /* host driver already reported errors */
> - } else {
> - if (cmd.resp[0] & R5_ERROR)
> - return -EIO;
> - if (cmd.resp[0] & R5_FUNCTION_NUMBER)
> - return -EINVAL;
> - if (cmd.resp[0] & R5_OUT_OF_RANGE)
> - return -ERANGE;
> - }
> + err = 0;
> + else if (cmd.resp[0] & R5_ERROR)
> + err = -EIO;
> + else if (cmd.resp[0] & R5_FUNCTION_NUMBER)
> + err = -EINVAL;
> + else if (cmd.resp[0] & R5_OUT_OF_RANGE)
> + err = -ERANGE;
> + else
> + err = 0;
>
> - return 0;
> + mmc_post_req(card->host, &mrq, err);
> +
> + if (nents > 1)
> + sg_free_table(&sgtable);
> +
> + return err;
> }
>
> int sdio_reset(struct mmc_host *host)
> --
> 2.17.1
>
