On Fri, Jul 11, 2025 at 06:13:05PM +0930, Qu Wenruo wrote: > [FAILURE] > Test case btrfs/282 still fails on some setup: > > output mismatch (see /opt/xfstests/results//btrfs/282.out.bad) > --- tests/btrfs/282.out 2025-06-27 22:00:35.000000000 +0200 > +++ /opt/xfstests/results//btrfs/282.out.bad 2025-07-08 20:40:50.042410321 +0200 > @@ -1,3 +1,4 @@ > QA output created by 282 > wrote 2147483648/2147483648 bytes at offset 0 > XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) > +scrub speed 2152038400 Bytes/s is not properly throttled, target is 1076019200 Bytes/s > ... > (Run diff -u /opt/xfstests/tests/btrfs/282.out /opt/xfstests/results//btrfs/282.out.bad to see the entire diff) > > [CAUSE] > Checking the full output, it shows the scrub is running too fast: > > Starting scrub on devid 1 > scrub done for c45c8821-4e55-4d29-8172-f1bf30b7182c > Scrub started: Tue Jul 8 20:40:47 2025 > Status: finished > Duration: 0:00:00 <<< > Total to scrub: 2.00GiB > Rate: 2.00GiB/s > Error summary: no errors found > Starting scrub on devid 1 > scrub done for c45c8821-4e55-4d29-8172-f1bf30b7182c > Scrub started: Tue Jul 8 20:40:48 2025 > Status: finished > Duration: 0:00:01 > Total to scrub: 2.00GiB > Rate: 2.00GiB/s > Error summary: no errors found > > The original run takes less than 1 seconds, making the scrub rate > calculation very unreliable, no wonder the speed limit is not able to > properly work. > > [FIX] > Instead of using fixed 2GiB file size, let the test create a filler for > 4 seconds with direct IO, this would more or less ensure the scrub will > take 4 seconds to run. > > With 4 seconds as run time, the scrub rate can be calculated more or > less reliably. > > Furthermore since btrfs-progs currently only reports scrub duration in > seconds, to prevent problems due to 1 second difference, enlarge the > tolerance to +/- 25%, to be extra safe. > > On my testing VM, the result looks like this: > > Starting scrub on devid 1 > scrub done for b542bdfb-7be4-44b3-add0-ad3621927e2b > Scrub started: Fri Jul 11 09:13:31 2025 > Status: finished > Duration: 0:00:04 > Total to scrub: 2.72GiB > Rate: 696.62MiB/s > Error summary: no errors found > Starting scrub on devid 1 > scrub done for b542bdfb-7be4-44b3-add0-ad3621927e2b > Scrub started: Fri Jul 11 09:13:35 2025 > Status: finished > Duration: 0:00:08 > Total to scrub: 2.72GiB > Rate: 348.31MiB/s > Error summary: no errors found > > However this exposed a new failure mode, that if the storage is too > fast, like the original report, that the initial 4 seconds write can > fill the fs and exit early. > > In that case we have no other solution but skipping the test case. Hi Qu, Thanks for tuning the test, we have also been facing intermittent failures on btrfs/282. I was just wondering if for faster devices, would it make sense to use the io cgroup controller, eg: echo "252:0 rbps=1048576 wbps=1048576" > /sys/fs/cgroup/io_limit/io.max To limit the throughput so we have >= 4s scrub runs. Or does that also have some undesired effects like you mentioned for dm_delay here [1] Regards, Ojaswin [1] https://lore.kernel.org/all/103e1b45-19d9-4438-b70d-892757f695fc@xxxxxxx/ > > Signed-off-by: Qu Wenruo <wqu@xxxxxxxx> > ---
