Re: [Xen-devel] [PATCH v8 00/10] qspinlock: a 4-byte queue spinlock with PV support

[Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>]

On 04/07/2014 10:08 PM, Waiman Long wrote:
> On 04/07/2014 02:14 AM, Raghavendra K T wrote:
[...]
> > But I am seeing hang in overcommit cases. Gdb showed that many vcpus
> > are halted and there was no progress. Suspecting the problem /race with
> > halting, I removed the halt() part of kvm_hibernate().  I am yet to
> > take a closer look at the code on halt() related changes.
> It seems like there may still be race conditions where the current code
> is not handling correctly. I will look into that to see where the
> problem is. BTW, what test do you use to produce the hang condition?
Running ebizzy on 2 of the vms simultaneously (for sometime in repeated 
loop) could reproduce it.
> > Patch series with that change gave around 20% improvement for dbench
> > 2x and 30% improvement for ebizzy 2x cases. (1x has no significant
> > loss/gain).
While at it, Just  a correction it was 30% for  ebizzy1.5x  and around
80% for ebizzy 2x.

> What is the baseline for the performance improvement? Is it without the
> unfair lock and PV qspinlock?
Baseline was 3.14-rc8 without any of the qspin patch series.


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