Re: [Xen-devel] Xen 4.3 development update

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 07/05/13 14:56, Pasi Kärkkäinen wrote:
> 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) ?
For the sake of people watching this thread: The last 4-5 mails I've 
sent to Peter Maloney have bounced with "Mailbox Full" messages; so it's 
possible he's not actually hearing this part of the discussion...
 -George

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