Re: Performance issue

[Gleb Natapov <gleb@redhat.com>]

On Thu, Nov 29, 2012 at 03:45:52PM +0200, George-Cristian Bîrzan wrote:
> On Thu, Nov 29, 2012 at 1:56 PM, Vadim Rozenfeld <vrozenfe@redhat.com> wrote:
> >> I've also added +hv_relaxed since then, but this is the command I'm
> >
> > I would suggest activating relaxed timing for all W2K8R2/Win7 guests.
> 
> Is there any place I can read up on the downsides of this for Linux,
> or is Just Better?
> 
You shouldn't use hyper-v flags for Linux guests. In theory Linux should
just ignore them, in practice there may be bugs that will prevent Linux
from detecting that it runs as a guest and disable optimizations.

> >>>> Other than that, was looking into a profiling trace of the software
> >> running and a lot of time (60%?) is spent calling two functions from
> >> hal.dll, HalpGetPmTimerSleepModePerfCounter when I disable HPET, and
> >> HalpHPETProgramRolloverTimer which do point at something related to
> >> the timers.
> >>
> > It means that hyper-v time stamp source was not activated.
> 
> I recompiled the whole kernel, with your patch, and while I cannot
> check at 70Mbps now, a test stream of 20 seems to do better. Also, now
> I don't see any of those functions, which used to account ~60% of the
> time spent by the program. I'm waiting for the customer to come back
> and start the 'real' stream, but from my tests, time spent in hal.dll
> is now an order of magnitude smaller.
> 
> --
> George-Cristian Bîrzan

--
			Gleb.