On 2014-06-17 07:27, Bart Van Assche wrote:
On 06/12/14 15:48, Christoph Hellwig wrote:
Bart and Robert have helped with some very detailed measurements that they
might be able to send in reply to this, although these usually involve
significantly reworked low level drivers to avoid other bottle necks.
In case someone would like to see the results of the measurements I ran,
these results can be found here:
https://docs.google.com/file/d/0B1YQOreL3_FxUXFMSjhmNDBNNTg.
Two important conclusions from the data in that PDF document are as follows:
- A small but significant performance improvement for the traditional
SCSI mid-layer (use_blk_mq=N).
- A very significant performance improvement for multithreaded
workloads with use_blk_mq=Y. As an example, the number of I/O
operations per second reported for the random write test increased
with 170%. That means 2.7 times the performance
of use_blk_mq=N.
Thanks for posting these numbers, Bart. The CPU utilization and IOPS
speak a very clear message. The only mystery is why the singe threaded
performance is down. That we need to get sort, but it's not a show
stopper for inclusion.
If you run the single threaded tests and watch for queue depths, is
there a difference between blk-mq=y/scsi-mq and the stock kernel?
I think this means the scsi-mq patches are ready for wider use.
I would agree. James, I haven't seen any comments from you on this yet.
I've run various bits of scsi-mq testing as well, and no ill effects
seen. On top of that, Christophs patches are nicely separated and have
general benefits even for the non-blk-mq cases. Time to shove them into
the queue for the next merge window?
--
Jens Axboe
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