Hello!
On Wed 03-01-24 11:31:39, Zhang Yi wrote:
> On 2024/1/2 15:31, kernel test robot wrote:
> >
> >
> > Hello,
> >
> > kernel test robot noticed a 92.5% regression of fileio.latency_95th_ms on:
>
> This seems a little weird, the tests doesn't use blk-cgroup, and the patch
> increase IO priority in WBT, so there shouldn't be any negative influence in
> theory.
I don't have a great explanation either but there could be some impact e.g.
due to a different request merging of IO done by JBD2 vs the flush worker or
something like that. Note that the throughput reduction is only 5.7% so it
is not huge.
> I've tested sysbench on my machine with Intel Xeon Gold 6240 CPU,
> 400GB memory with HDD disk, and couldn't reproduce this regression.
>
> ==
> Without 6a3afb6ac6 ("jbd2: increase the journal IO's priority")
> ==
>
> $ sysbench fileio --events=0 --threads=128 --time=600 --file-test-mode=seqwr --file-total-size=68719476736 --file-io-mode=sync --file-num=1024 run
>
> sysbench 1.1.0-df89d34 (using bundled LuaJIT 2.1.0-beta3)
>
> Running the test with following options:
> Number of threads: 128
> Initializing random number generator from current time
>
>
> Extra file open flags: (none)
> 1024 files, 64MiB each
> 64GiB total file size
> Block size 16KiB
> Periodic FSYNC enabled, calling fsync() each 100 requests.
> Calling fsync() at the end of test, Enabled.
> Using synchronous I/O mode
> Doing sequential write (creation) test
> Initializing worker threads...
>
> Threads started!
>
>
> Throughput:
> read: IOPS=0.00 0.00 MiB/s (0.00 MB/s)
> write: IOPS=31961.19 499.39 MiB/s (523.65 MB/s)
> fsync: IOPS=327500.24
Well, your setup seems to be very different from what LKP was using. You
are achieving ~500 MB/s (likely because all the files fit into the cache
and more or less even within the dirty limit of the page cache) while LKP
run achieves only ~54 MB/s (i.e., we are pretty much bound by the rather
slow disk). I'd try running with something like 32GB of RAM to really see
the disk speed impact...
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
