On 30/05/18 11:44, Adrian Hunter wrote: > On 28/05/18 09:26, Christoph Hellwig wrote: >> Summary: mke2s uses the BLKDISCARD ioctl to wipe the device, >> and then uses BLKDISCARDZEROES to check if that zeroed the data. >> >> A while ago I made BLKDISCARDZEROES always return 0 because it is >> basically impossible to have reliably zeroing using discard as the >> standards leave the devices way to many options to not actually >> zero data at their own choice when using the discard commands. > > Older eMMC do not have a "discard" option and use "erase" instead. "Erase" > has similar benefits to "discard" but the eMMC is required to make the > erased blocks read as either all 0's or all 1's. > >> >> So IFF mke2fs want to actually free space and zero it it needs >> to use fallocate to punch a hole, and mmc needs to implement >> REQ_OP_WRITE_ZEROS IFF it actually has a reliable way to zero >> blocks. >> >> >> On Tue, May 22, 2018 at 08:48:31PM +0530, Faiz Abbas wrote: >>> Hi, >>> >>> I am debugging a performance reduction in ext2 filesystems on an mmc >>> device in TI's am335x evm board. >>> >>> I see that the performance is reduced on the first write after making a >>> new filesystem using mkfs.ext2 on one of the mmc partitions. The >>> performance comes back to normal after the first write. >>> >>> commands used: >>> >>> => umount /dev/mmcblk1p2 >>> >>> => mkfs.ext2 -F /dev/mmcblk1p2 >>> >>> => mount -t ext2 -o async /dev/mmcblk1p2 /mnt/partition_mmc >>> >>> => dd if=/dev/urandom of=/dev/shm/srctest_file_mmc_1184 bs=1M count=10 >>> >>> => ./filesystem_tests -write -src_file /dev/shm/srctest_file_mmc_1184 >>> -srcfile_size 10 -file /mnt/partition_mmc/test_file_1184 -buffer_size >>> 102400 -file_size 100 -performance >>> >>> The filesystem_tests write utility reads from the file generated at >>> /dev/shm/srctest_file_mmc_1184, memory maps the file to a buffer, and >>> then writes it into the newly created /mnt/partition_mmc in multiples of >>> buffer_size while measuring write performance. >>> >>> See here for the implementation of filesystem_tests write utility: >>> http://arago-project.org/git/projects/?p=test-automation/ltp-ddt.git;a=blob;f=testcases/ddt/filesystem_test_suite/src/testcases/st_filesystem_write_to_file.c;h=80e8e244d7eaa9f0dbd9b21ea705445156c36bef;hb=f7fc06c290333ce08a7d4fba104eee0f0f1d942b >>> >>> Complete log with multiple calls to filesystem_tests: >>> https://pastebin.ubuntu.com/p/BckmTJpqPv/ >>> >>> Notice that the first run of filesystem_tests has a lower throughput >>> reported. >>> >>> I was able to bisect the issue to this commit: >>> 5d1429fead5b (mmc: remove the discard_zeroes_data flag) >>> >>> I would assume that after this flag is removed, the filesystem creation >>> command would explicitly write zeroes to the device which might explain >>> the performance fall. However, then the mkfs.ext2 command itself should >>> take more time rather than the first file write after that. > > You might want to check the lazy initialization options. I always use > "-Elazy_itable_init=0,lazy_journal_init=0" with ext4 to prevent it messing > up performance tests. And discards are not enabled by default by mount so, at least on ext4, adding "-o discard" is needed in the mount options.
