On 01/06/15 14:32, David Jander wrote: > On Mon, 01 Jun 2015 13:36:45 +0300 > Adrian Hunter <adrian.hunter@xxxxxxxxx> 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 <david@xxxxxxxxxxx> >>> --- >>> 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? Not necessarily. You could regard the "can only do 1 erase block at a time" case as special, flag it, and in that case have mmc_erase() split along erase block boundaries and call mmc_do_erase() multiple times. Then you could set max_discard to something arbitrarily bigger. > Has anybody even started to look into this? Ulf was looking at supporting R1 response instead of R1b response from the erase command and using a software timeout instead of the host controller's hardware timeout. -- 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
