On 6/13/19 1:20 AM, Jan Kara wrote:

On Wed 12-06-19 12:36:53, Srivatsa S. Bhat wrote:

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[ Adding Greg to CC ]

On 6/12/19 6:04 AM, Jan Kara wrote:

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On Tue 11-06-19 15:34:48, Srivatsa S. Bhat wrote:

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On 6/2/19 12:04 AM, Srivatsa S. Bhat wrote:

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On 5/30/19 3:45 AM, Paolo Valente wrote:

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[...]

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At any rate, since you pointed out that you are interested in
out-of-the-box performance, let me complete the context: in case
low_latency is left set, one gets, in return for this 12% loss,
a) at least 1000% higher responsiveness, e.g., 1000% lower start-up
times of applications under load [1];
b) 500-1000% higher throughput in multi-client server workloads, as I
already pointed out [2].

I'm very happy that you could solve the problem without having to
compromise on any of the performance characteristics/features of BFQ!

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I'm going to prepare complete patches.  In addition, if ok for you,
I'll report these results on the bug you created.  Then I guess we can
close it.

Sounds great!

Hi Paolo,

Hope you are doing great!

I was wondering if you got a chance to post these patches to LKML for
review and inclusion... (No hurry, of course!)

Also, since your fixes address the performance issues in BFQ, do you
have any thoughts on whether they can be adapted to CFQ as well, to
benefit the older stable kernels that still support CFQ?

Since CFQ doesn't exist in current upstream kernel anymore, I seriously
doubt you'll be able to get any performance improvements for it in the
stable kernels...

I suspected as much, but that seems unfortunate though. The latest LTS
kernel is based on 4.19, which still supports CFQ. It would have been
great to have a process to address significant issues on older
kernels too.

Well, you could still tune the performance difference by changing
slice_idle and group_idle tunables for CFQ (in
/sys/block/<device>/queue/iosched/).  Changing these to lower values will
reduce the throughput loss when switching between cgroups at the cost of
lower accuracy of enforcing configured IO proportions among cgroups.

Good point, and seems fair enough, thank you!

Regards,
Srivatsa
VMware Photon OS