Re: Performance issue

[Vadim Rozenfeld <vrozenfe@redhat.com>]

On Thursday, November 29, 2012 03:56:10 PM Gleb Natapov wrote:
> 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.
> 
As Gleb said, hyper-v flag are relevant to the Windows guests only. 
IIRC spinlocks and vapic should work for Vista and higher. Relaxed timing and
partition reference time work for Win7/W2K8R2.
> > >>>> 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.