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. Regards Dong Aisheng > /* Convert qty to sectors */ > if (card->erase_shift) > -- > 1.8.1.5 > -- 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
