On Mon, 01 Jun 2015 13:36:45 +0300 Adrian Hunter <adrian.hun...@intel.com> wrote:
> On 01/06/15 12:20, David Jander wrote: > > qty is the maximum number of discard that _do_ fit in the timeout, not > > the first amount that does _not_ fit anymore. > > This seemingly harmless error has a very severe performance impact when > > the timeout value is enough for only 1 erase group. > > > > Signed-off-by: David Jander <da...@protonic.nl> > > --- > > drivers/mmc/core/core.c | 7 ++----- > > 1 file changed, 2 insertions(+), 5 deletions(-) > > > > diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c > > index 92e7671..1f9573b 100644 > > --- a/drivers/mmc/core/core.c > > +++ b/drivers/mmc/core/core.c > > @@ -2234,16 +2234,13 @@ static unsigned int mmc_do_calc_max_discard(struct > > mmc_card *card, if (!qty) > > return 0; > > > > - if (qty == 1) > > - return 1; > > - > > /* Convert qty to sectors */ > > if (card->erase_shift) > > - max_discard = --qty << card->erase_shift; > > + max_discard = qty << card->erase_shift; > > else if (mmc_card_sd(card)) > > max_discard = qty; > > else > > - max_discard = --qty * card->erase_size; > > + max_discard = qty * card->erase_size; > > > > return max_discard; > > } > > > > This keeps coming up but there is more to it than that. See here: > > http://marc.info/?l=linux-mmc&m=142504164427546 > Thanks for the link. I think it is time to put a comment on that piece of code to clarify this. Also, this code badly needs optimizing. I happen to have one of those unfortunate cases, where the maximum timeout of the MMC controller (Freescale i.MX6 uSDHCI) is 5.4 seconds, and the eMMC device (Micron 16GB eMMC) TRIM_MULT is 15 (4.5 seconds). As a result mmc_do_calc_max_discard() returns 1 and mkfs.ext4 takes several hours!! I think it is pretty clear that this is unacceptable and needs to be fixed. AFAICS, the "correct fix" for this would implicate that discard knows about the erase-group boundaries... something that could reach into the block-layer even... right? Has anybody even started to look into this? Best regards, -- David Jander Protonic Holland. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
