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

[Waiman Long]

On 04/02/2014 04:35 PM, Waiman Long wrote:
> On 04/02/2014 10:32 AM, Konrad Rzeszutek Wilk wrote:
> > On Wed, Apr 02, 2014 at 09:27:29AM -0400, Waiman Long wrote:
> > > N.B. Sorry for the duplicate. This patch series were resent as the
> > >       original one was rejected by the vger.kernel.org list server
> > >       due to long header. There is no change in content.
> > >
> > > v7->v8:
> > >    - Remove one unneeded atomic operation from the slowpath, thus
> > >      improving performance.
> > >    - Simplify some of the codes and add more comments.
> > >    - Test for X86_FEATURE_HYPERVISOR CPU feature bit to enable/disable
> > >      unfair lock.
> > >    - Reduce unfair lock slowpath lock stealing frequency depending
> > >      on its distance from the queue head.
> > >    - Add performance data for IvyBridge-EX CPU.
> > FYI, your v7 patch with 32 VCPUs (on a 32 cpu socket machine) on an
> > HVM guest under Xen after a while stops working. The workload
> > is doing 'make -j32' on the Linux kernel.
> >
> > Completely unresponsive. Thoughts?
>
> Thank for reporting that. I haven't done that much testing on Xen. My 
> focus was in KVM. I will perform more test on Xen to see if I can 
> reproduce the problem.

BTW, does the halting and sending IPI mechanism work in HVM? I saw that 
in RHEL7, PV spinlock was explicitly disabled when in HVM mode. However, 
this piece of code isn't in upstream code. So I wonder if there is 
problem with that.

-Longman
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