On 1 June 2015 at 15:32, David Jander <david@xxxxxxxxxxx> wrote: > 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? It's been forever in my TODO list. It would be great if you could take a closer look, I will happily review your patches. As note, a while ago I fixed similar busy timeout issues for the switch commands (CMD6). You can likely be influenced by that to find out what makes sense for the erase command. Kind regards Uffe -- 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
