On Mon, 01 Jun 2015 15:38:51 +0300 Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote: > On 01/06/15 15:30, David Jander wrote: > > On Mon, 01 Jun 2015 14:50:47 +0300 > > Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote: > > > >> 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. > > > > Right. I was just looking at mmc_erase() and thought about splitting the > > erase at the next boundary if it was not aligned. That way my patch could > > be used in every case, since we would ensure that mmc_do_erase() will > > always start erase-group aligned. Would you agree to such a solution? > > Why would people who don't have your problem want their erase performance > potentially degraded by unnecessary splitting. This penalty would exist only when erasing a small amount of sectors. If we approach the timeout limit, this penalty is canceled-out by the gain of being able to erase double the amount of sectors in one operation. I have no idea what the typical workload of this function will be, so I take your hint and treat the "can only do 1 erase block at a time" case as special. >[...] > >>> 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. > > > > That would also be an option, specially if the TRIM_MULT becomes larger > > than what the controller can handle! > > @Ulf: How far are you with this? Still wonder about this case, though... Best regards, -- David Jander Protonic Holland. -- 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
