Re: [PATCH] mmc: mkfs takes hours on some combinations of eMMC device and host controller

[Adrian Hunter <adrian.hunter@intel.com>]

On 25/02/15 23:55, Al Cooper wrote:
> mkfs.ext4 will erase the entire partition on the eMMC device before
> writing the actual filesystem. The number of blocks erased on each
> erase eMMC command is determined at run time based on the max erase
> or trim time specified by the EXT_CSD in the eMMC device and the max eMMC
> command timeout supported by the host controller. The routine in the
> kernel that calculates the max number of blocks specified per command
> returns 1 with some combinations of host controllers with a short max
> command timeout and eMMC devices with long max erase or trim time.
> This will end up requiring over 8 million erase sequences on a 4GB
> eMMC partition and will take many hours.
> 
> For example, on a host controller with a 50MHz timeout clock
> specified in the Host CAPS register and an eMMC device
> with a TRIM Multiplier of 6 specified in the EXT_CSD we get
> 2^27/50000000=2.68 secs for a max command timeout and 6*.300=1.8 secs
> for a trim operation which only allows 1 per trim command. The problem
> seems to be in mmc_do_calc_max_discard() which does it's calculations
> based on erase blocks but converts to and returns write blocks
> (2MB blocks to 512 bytes blocks for a typical eMMC device) unless
> the value is 1 in which case it just returns the 1. The routine also
> subtracts 1 from the max calculation before converting from erase to
> write blocks which should not be needed.
> 
> This change will convert all non-zero max calculations from erase
> to write blocks and will no longer subtract 1 from the erase block
> max before converting to write blocks. This allow mkfs.ext4 to run
> in 30 secs instead of >10 hours.
> 
> Signed-off-by: Al Cooper <alcooperx@gmail.com>
> ---
>  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 23f10f7..1b61ac0 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -2231,16 +2231,13 @@ 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 has been covered before:

	http://marc.info/?l=linux-mmc&m=138736492823089&w=2