Hi Everyone, I am debugging a performance degradation issue in some SD cards which happened around 4.13 kernel on TI's AM335x-evm. I compare the time taken for a simple dd command (after dropping caches) to run between kernel versions 4.13 and 4.14. I see that there is a consistent 15-20% reduction in speed. The amount of decrease depends on the card used. command: # echo 3 > /proc/sys/vm/drop_caches; dd if=/dev/zero of=/dev/mmcblk1p2 bs=1M count=100; v4.13 ~22s for 100M transfer v4.14 ~28s for 100M transfer Also, I see many times the number of interrupts for mmc1 in 4.14. v4.14 34: 2122 INTC 64 Level mmc1 v4.13 162: 457 INTC 64 Level mmc1 This increase of interrupts also exists in the latest kernel. I also printed out the size of the DMA transfers in the omap_hsmmc driver during the dd command. I see that the maximum size of the dma transfer has decreased from 1 MB to 256kB between 4.13 and 4.14. Full log: v4.13 https://pastebin.ubuntu.com/p/gK2k9GZcNd/ v4.14 https://pastebin.ubuntu.com/p/3YzCbQ79rk/ It looks like something has started splitting the request into 4 times as many smaller buffers and this is what is causing the performance decrease. I also ran the ftrace function profile tool on mmc* and blk* functions and see that the function mmc_blk_issue_rq() is where the program spends most of its time and the calls to that and other related functions have increased around 4 times with the average time per call being reduced. Function profile Log: v4.13 https://pastebin.ubuntu.com/p/R5JG6FpTvy/ v4.14 https://pastebin.ubuntu.com/p/Kc6QYYwYcN/ I am not sure why calls to mmc_blk_issue_rq() have increased by so much. Any ideas why this could be happening? Thanks, Faiz -- 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
