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. >> >> It would be nice if someone could help me understand why this is happening. >> >> Thanks for your help. >> >> Regards, >> Faiz > ---end quoted text--- >
