On 12/18/2015 04:08 PM, Hannes Reinecke wrote:
On 12/18/2015 03:58 PM, John Garry wrote:
Hi,
I have started to enable scsi-mq on the HiSilicon SAS driver.
Are there hints/checks I should use to make sure it is configured
correctly/optimally? In my initial testing I have seen some
performance improvements, but none like what I have seen in
presentations.
The whole thing is build around having symmetric submit and receive
queues, so that we can tack a send/receive queue pair to the same CPU.
With that we can ensure that we don't have any cache invalidation, as
the request is already in the cache for that CPU when the completion is
recieved. _And_ we can get rid of most spinlocks as other CPUs cannot
access our request.
So make sure to have the submit and receive queues properly done, and
ensure you don't have any global resources within your driver which
needs to be locked. Or move access to those resources out of the fast path.
Hello John,
It's great news that you started looking into scsi-mq support :-) As
Hannes wrote, if the performance improvement is not as big as you
expected this could be caused e.g. by lock contention. Are you familiar
with the perf tool ? The perf tool can be a great help to verify whether
lock contention occurs and also which lock(s) cause it.
Bart.
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