A significant increase (10-20%) in performance throughput for USB mass storage is the reason for incrementing the value. By some reason the USB driver allocates buffers which requires a scattergather list to contain a lot more than 16 elements to get optimal performance. This change sets the maximum elements to 128. Tests with large reads and large writes (100 MiB) show that the throughput increase is significant for write (10% for this test) but not for read. Tests are run on a Linux host with ext4 FS on the gadget mass storage device. The sg-len still exceeds 16 for the read tests but the performance gain is low or nothing. Signed-off-by: Ulf Hansson <ulf.hansson@xxxxxxxxxxxxxx> Signed-off-by: Per Forlin <per.forlin@xxxxxxxxxxxxxx> Acked-by: Linus Walleij <linus.walleij@xxxxxxxxxx> --- drivers/mmc/host/mmci.h | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/drivers/mmc/host/mmci.h b/drivers/mmc/host/mmci.h index 79e4143..49f153e 100644 --- a/drivers/mmc/host/mmci.h +++ b/drivers/mmc/host/mmci.h @@ -160,7 +160,7 @@ (MCI_RXFIFOHALFFULLMASK | MCI_RXDATAAVLBLMASK | \ MCI_TXFIFOHALFEMPTYMASK) -#define NR_SG 16 +#define NR_SG 128 struct clk; struct variant_data; -- 1.7.5.4 -- 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
