On Wed, Jun 27, 2012 at 07:02:45PM -0400, Eric Sandeen wrote: > > fallocate 1g, do 16m of 4k random IOs, sync after each: > > # for I in a b c; do rm -f testfile; echo 3 > /proc/sys/vm/drop_caches; fio tytso.fio | grep 2>&1 WRITE; done > > WRITE: io=16384KB, aggrb=154KB/s, minb=158KB/s, maxb=158KB/s, mint=105989msec, maxt=105989msec > WRITE: io=16384KB, aggrb=163KB/s, minb=167KB/s, maxb=167KB/s, mint=99906msec, maxt=99906msec > WRITE: io=16384KB, aggrb=176KB/s, minb=180KB/s, maxb=180KB/s, mint=92791msec, maxt=92791msec > > same, but overwrite pre-written 1g file (same as the expose-my-data option ;) > > # dd if=/dev/zero of=testfile bs=1M count=1024 > # for I in a b c; do echo 3 > /proc/sys/vm/drop_caches; fio tytso.fio | grep 2>&1 WRITE; done > > WRITE: io=16384KB, aggrb=164KB/s, minb=168KB/s, maxb=168KB/s, mint=99515msec, maxt=99515msec > WRITE: io=16384KB, aggrb=164KB/s, minb=168KB/s, maxb=168KB/s, mint=99371msec, maxt=99371msec > WRITE: io=16384KB, aggrb=164KB/s, minb=168KB/s, maxb=168KB/s, mint=99677msec, maxt=99677msec > There's a pretty large range comparing the first set versus the second set of numbers. With the second set of numbers, the times are much more stable. I wonder if one of the things that's going on is file placement; if you're constantly deleting and recreating the file, are we getting the same block numbers or not? (And if we're not, is that something we need to look at vis-a-vis the block allocator --- especially with SSD's?) - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
