On 12/19/2013 01:39 AM, Dong Aisheng wrote: > On Thu, Dec 19, 2013 at 6:27 AM, Stephen Warren <swarren@xxxxxxxxxxxxx> wrote: >> From: Stephen Warren <swarren@xxxxxxxxxx> >> >> In mmc_do_calc_max_discard(), if only a single erase block can be >> discarded within the host controller's timeout, don't allow discard >> operations at all. >> >> Previously, the code allowed sector-at-a-time discard (rather than >> erase-block-at-a-time), which was chronically slow. >> >> Without this patch, on the NVIDIA Tegra Cardhu board, the loops result >> in qty == 1, which is immediately returned. This causes discard to >> operate a single sector at a time, which is chronically slow. With this >> patch in place, discard operates a single erase block at a time, which >> is reasonably fast. >> >> Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx> >> Cc: Dong Aisheng <dongas86@xxxxxxxxx> >> Cc: Ulf Hansson <ulf.hansson@xxxxxxxxxx> >> Cc: Vladimir Zapolskiy <vz@xxxxxxxxx> >> Fixes: e056a1b5b67b "(mmc: queue: let host controllers specify maximum discard timeout") >> Signed-off-by: Stephen Warren <swarren@xxxxxxxxxx> >> --- >> drivers/mmc/core/core.c | 21 +++++++++++++++++++-- >> 1 file changed, 19 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c >> index 57a2b403bf8e..eb952ca634ea 100644 >> --- a/drivers/mmc/core/core.c >> +++ b/drivers/mmc/core/core.c >> @@ -2150,8 +2150,25 @@ static unsigned int mmc_do_calc_max_discard(struct mmc_card *card, >> if (!qty) >> return 0; >> >> - if (qty == 1) >> - return 1; >> + /* >> + * Discard operations may not be aligned to an erase block. In an >> + * unaligned case, we need to issue 1 more discard operation to HW >> + * than strictly calculated by: >> + * sectors_to_erase / sectors_per_discard_operation >> + * >> + * To account for this in the timeout calculations, we assume we can >> + * actually discard one less erase block than fits into the HW >> + * timeout. This explains the --qty below. >> + * >> + * When only a single discard block operation fits into the timeout, >> + * disallow any discard operations at all. For example, discarding one >> + * sector at a time is so chronically slow as to be useless. However, >> + * make an exception for SD cards without an erase shift, since qty >> + * isn't multiplied up by an erase block size in the code below for >> + * that case. >> + */ >> + if (qty == 1 && !(!card->erase_shift && mmc_card_sd(card))) >> + return 0; >> > > How about when qty == 2? > Erase 2 sectors may have no much difference from 1 sector per one time > for a SD card, > it may still chronically slow, i guess. > So i wonder it may not sovle the issues totally. When qty==2, the number of sectors gets multiplied by the number of sectors in an erase block, so it isn't chronically slow. It's only slow with qty==1 because without this patch, the multiplication gets skipped and "1" returned rather then "1 << card->erase_shift". -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
