Re: [Qemu-devel] [PATCH] memory: synchronize dirty bitmap before unmapping a range

[Avi Kivity <avi@redhat.com>]

On 08/01/2011 10:52 AM, Jan Kiszka wrote:
> On 2011-08-01 09:34, Jan Kiszka wrote:
> >  On 2011-07-31 21:47, Avi Kivity wrote:
> >>  When a range is being unmapped, ask accelerators (e.g. kvm) to synchronize the
> >>  dirty bitmap to avoid losing information forever.
> >>
> >>  Fixes grub2 screen update.
> >
> >  I does.
> >
> >  But something is still broken. As I reported before, the performance of
> >  grub2 startup is an order of magnitude slower than with the existing
> >  code. According to ftrace, we are getting tons of additional
> >  EPT_MISCONFIG exits over the 0xA0000 segment. But I haven't spot the
> >  difference yet. The effective slot setup as communicated to kvm looks
> >  innocent.
>
> I take it back: We obviously once in a while resume the guest with the
> vga segment unmapped. And that, of course, ends up doing mmio instead of
> plain ram accesses.
>

qemu-kvm.git 6b5956c573 and its predecessor fix the issue (and I think 
they're even faster than upstream, but perhaps I'm not objective).

-- 
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