Re: [Xen-devel] Xen 4.3 development update

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Mon, Apr 29, 2013 at 03:21:34PM +0200, Peter Maloney wrote:
> On 04/04/2013 07:05 PM, Tim Deegan wrote:
> > At 16:23 +0100 on 04 Apr (1365092601), Tim Deegan wrote:
> >> At 11:34 -0400 on 03 Apr (1364988853), Andres Lagar-Cavilla wrote:
> >>> On Apr 3, 2013, at 6:53 AM, George Dunlap <george.dunlap@xxxxxxxxxxxxx> 
> >>> wrote:
> >> Yes, 4.2 is definitely slower.  A compile test on a 4-vcpu VM that takes
> >> about 12 minutes before this locking change takes more than 20 minutes
> >> on the current tip of xen-unstable (I gave up at 22 minutes and rebooted
> >> to test something else).
> > I did a bit of prodding at this, but messed up my measurements in a
> > bunch of different ways over the afternoon. :(  I'm going to be away
> > from my test boxes for a couple of weeks now, so all I can say is, if
> > you're investigating this bug, beware that:
> >
> >  - the revision before this change still has the RTC bugs that were
> >    fixed last week, so don't measure performance based on guest
> >    wallclock time, or your 'before' perf will look too good.
> >  - the current unstable tip has test code to exercise the new
> >    map_domain_page(), which will badly affect all the many memory
> >    accesses done in HVM emulation, so make sure you use debug=n builds
> >    for measurement.
> >
> > Also, if there is still a bad slowdown, caused by the p2m lookups, this
> > might help a little bit:
> >
> > diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
> > index 38e87ce..7bd8646 100644
> > --- a/xen/arch/x86/hvm/hvm.c
> > +++ b/xen/arch/x86/hvm/hvm.c
> > @@ -1361,6 +1361,18 @@ int hvm_hap_nested_page_fault(paddr_t gpa,
> >          }
> >      }
> >  
> > +
> > +    /* For the benefit of 32-bit WinXP (& older Windows) on AMD CPUs,
> > +     * a fast path for LAPIC accesses, skipping the p2m lookup. */
> > +    if ( !nestedhvm_vcpu_in_guestmode(v)
> > +         && gfn == vlapic_base_address(vcpu_vlapic(current)) >> PAGE_SHIFT 
> > )
> > +    {
> > +        if ( !handle_mmio() )
> > +            hvm_inject_hw_exception(TRAP_gp_fault, 0);
> > +        rc = 1;
> > +        goto out;
> > +    }
> > +
> >      p2m = p2m_get_hostp2m(v->domain);
> >      mfn = get_gfn_type_access(p2m, gfn, &p2mt, &p2ma, 
> >                                P2M_ALLOC | (access_w ? P2M_UNSHARE : 0), 
> > NULL);
> This patch (applied to 4.2.2) has a very large improvement on my box
> (AMD FX-8150) and WinXP 32 bit.
> 
> It only took about 2.5 minutes to log in and see task manager. It takes
> about 6 minutes without the patch. And 2.5 minutes is still terrible,
> but obviously better.
>

So is the problem only on WinXP with "booting up / logging in to windows", 
or do you see performance regressions on some actual benchmark tools aswell 
(after windows has started up) ?

-- Pasi


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