Re: [PATCH RFC V8 0/17] Paravirtualized ticket spinlocks

On 05/07/2012 04:46 PM, Srivatsa Vaddagiri wrote:

* Raghavendra K T [off-list ref] [2012-05-07 19:08:51]:

quoted

I 'll get hold of a PLE mc  and come up with the numbers soon. but I
'll expect the improvement around 1-3% as it was in last version.

Deferring preemption (when vcpu is holding lock) may give us better than 1-3% 
results on PLE hardware. Something worth trying IMHO.

Is the improvement so low, because PLE is interfering with the patch, or
because PLE already does a good job?

-- 
error compiling committee.c: too many arguments to function

On 05/07/2012 07:19 PM, Avi Kivity wrote:

On 05/07/2012 04:46 PM, Srivatsa Vaddagiri wrote:

quoted

* Raghavendra K T[off-list ref]  [2012-05-07 19:08:51]:

quoted

I 'll get hold of a PLE mc  and come up with the numbers soon. but I
'll expect the improvement around 1-3% as it was in last version.

Deferring preemption (when vcpu is holding lock) may give us better than 1-3%
results on PLE hardware. Something worth trying IMHO.

Is the improvement so low, because PLE is interfering with the patch, or
because PLE already does a good job?

It is because PLE already does a good job (of not burning cpu). The
1-3% improvement is because, patchset knows atleast who is next to hold
lock, which is lacking in PLE.

* Avi Kivity [off-list ref] [2012-05-07 16:49:25]:

quoted

Deferring preemption (when vcpu is holding lock) may give us better than 1-3% 
results on PLE hardware. Something worth trying IMHO.

Is the improvement so low, because PLE is interfering with the patch, or
because PLE already does a good job?

I think its latter (PLE already doing a good job). 

- vatsa

On 05/07/2012 06:49 AM, Avi Kivity wrote:

On 05/07/2012 04:46 PM, Srivatsa Vaddagiri wrote:

quoted

* Raghavendra K T [off-list ref] [2012-05-07 19:08:51]:

quoted

I 'll get hold of a PLE mc  and come up with the numbers soon. but I
'll expect the improvement around 1-3% as it was in last version.

Deferring preemption (when vcpu is holding lock) may give us better than 1-3% 
results on PLE hardware. Something worth trying IMHO.

Is the improvement so low, because PLE is interfering with the patch, or
because PLE already does a good job?

How does PLE help with ticket scheduling on unlock?  I thought it would
just help with the actual spin loops.

    J

On 05/08/2012 04:45 AM, Jeremy Fitzhardinge wrote:

On 05/07/2012 06:49 AM, Avi Kivity wrote:

quoted

On 05/07/2012 04:46 PM, Srivatsa Vaddagiri wrote:

quoted

* Raghavendra K T[off-list ref]  [2012-05-07 19:08:51]:

quoted

I 'll get hold of a PLE mc  and come up with the numbers soon. but I
'll expect the improvement around 1-3% as it was in last version.

Deferring preemption (when vcpu is holding lock) may give us better than 1-3%
results on PLE hardware. Something worth trying IMHO.

Is the improvement so low, because PLE is interfering with the patch, or
because PLE already does a good job?

How does PLE help with ticket scheduling on unlock?  I thought it would
just help with the actual spin loops.

Hmm. This strikes something to me. I think I should replace while 1 hog
in with some *real job*  to measure over-commit case. I hope to see
greater improvements because of fairness and scheduling of the
patch-set.

May be all the way I was measuring something equal to 1x case.

On 05/08/2012 02:15 AM, Jeremy Fitzhardinge wrote:

On 05/07/2012 06:49 AM, Avi Kivity wrote:

quoted

On 05/07/2012 04:46 PM, Srivatsa Vaddagiri wrote:

quoted

* Raghavendra K T [off-list ref] [2012-05-07 19:08:51]:

quoted

I 'll get hold of a PLE mc  and come up with the numbers soon. but I
'll expect the improvement around 1-3% as it was in last version.

Deferring preemption (when vcpu is holding lock) may give us better than 1-3% 
results on PLE hardware. Something worth trying IMHO.

Is the improvement so low, because PLE is interfering with the patch, or
because PLE already does a good job?

How does PLE help with ticket scheduling on unlock?  I thought it would
just help with the actual spin loops.

PLE yields to up a random vcpu, hoping it is the lock holder.  This
patchset wakes up the right vcpu.  For small vcpu counts the difference
is a few bad wakeups (and even a bad wakeup sometimes works, since it
can put the spinner to sleep for a bit).  I expect that large vcpu
counts would show a greater difference.

-- 
error compiling committee.c: too many arguments to function