Messages in this thread | | | From | Jeff Moyer <> | Subject | Re: [PATCH 0/2] cfq-iosched: fixing RQ_NOIDLE handling. | Date | Tue, 13 Jul 2010 15:38:11 -0400 |
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Corrado Zoccolo <czoccolo@gmail.com> writes:
> Can you test the attached patch, where I also added your changes to > make jbd(2) to perform sync writes?
I got new storage, so I have new numbers. I only re-ran deadline and vanilla cfq for the fs_mark only test. The average of 10 runs comes out like so:
deadline: 571.98 vanilla cfq: 107.42 patched cfq: 460.9
Mixed workload results with your suggested patch:
fs_mark: 15.65 files/sec fio: 132.5 MB/s
So, again, not looking great for the mixed workload, but the patch does improve the fs_mark only case. Looking at the blktrace data shows that the jbd2 thread preempts the fs_mark thread at all the right times. The only thing holding throughput back is the whole notion that we need to only dispatch from one queue (even though the storage is capable of serving both the reads and writes simultaneously).
I added in the patch that allows the simultaneous dispatch of both reads and writes, and here are the results from that run:
fs_mark: 15.975 files/sec fio: 132.4 MB/s
So, it looks like that didn't help. The reason this patch doesn't come close to the yield patch in the mixed workload is because the yield patch set allows the fs_mark process to continue to issue I/O. With your patch, the fs_mark process does 64KB of I/O, the jbd2 thread does the journal commit, and then the fio process runs again. Given that the fs_mark process typically only uses a small fraction of its time slice, you end up with an unfair balance.
Now, we still have to decide whether that's a problem that needs solving. I tried to gather data from the field, but I've been unable to conclusively say whether an application issues this sort of dependent I/O.
As such, I am happy with this patch. If we see that we need something like the blk_yield approach, then I'm happy to resurrect that work.
Jens, do you find that an agreeable solution? If so, you can add my signed-off-by and tested-by to the patch that Corrado posted.
Cheers, Jeff
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