Re: [Qemu-devel] Slow PXE boot in qemu.git (fast in qemu-kvm.git)

[Luiz Capitulino <lcapitulino@redhat.com>]

On Fri, 08 Apr 2011 19:50:57 -0500
Anthony Liguori <anthony@codemonkey.ws> wrote:

> On 04/08/2011 06:25 PM, Luiz Capitulino wrote:
> > Hi there,
> >
> > Summary:
> >
> >   - PXE boot in qemu.git (HEAD f124a41) is quite slow, more than 5 minutes. Got
> >     the problem with e1000, virtio and rtl8139. However, pcnet *works* (it's
> >     as fast as qemu-kvm.git)
> >
> >   - PXE boot in qemu-kvm.git (HEAD df85c051) is fast, less than a minute. Tried
> >     with e1000, virtio and rtl8139 (I don't remember if I tried with pcnet)
> >
> > I tried with qemu.git v0.13.0 in order to check if this was a regression, but
> > I got the same problem...
> >
> > Then I inspected qemu-kvm.git under the assumption that it could have a fix
> > that wasn't commited to qemu.git. Found this:
> >
> >   - commit 0836b77f0f65d56d08bdeffbac25cd6d78267dc9 which is merge, works
> >
> >   - commit cc015e9a5dde2f03f123357fa060acbdfcd570a4 does not work (it's slow)
> >
> > I tried a bisect, but it brakes due to gcc4 vs. gcc3 changes. Then I inspected
> > commits manually, and found out that commit 64d7e9a4 doesn't work, which makes
> > me think that the fix could be in the conflict resolution of 0836b77f, which
> > makes me remember that I'm late for diner, so my conclusions at this point are
> > not reliable :)
> 
> Can you run kvm_stat to see what the exit rates are?

Here you go, both collected after the VM is fully booted:

qemu.git:

efer_reload                    0         0
exits                  159767195        99
fpu_reload                   203         0
halt_exits                   544        27
halt_wakeup                    0         0
host_state_reload         299851        70
hypercalls                     0         0
insn_emulation         134495973        41
insn_emulation_fail            0         0
invlpg                      9687         0
io_exits                   85979         0
irq_exits                 162179         4
irq_injections             11582        27
irq_window                 20712        27
largepages                     0         0
mmio_exits                  9545        41
mmu_cache_miss              5307         0
mmu_flooded                 2493         0
mmu_pde_zapped              1188         0
mmu_pte_updated             5355         0
mmu_pte_write             181550         0
mmu_recycled                   0         0
mmu_shadow_zapped           6437         0
mmu_unsync                    15         0
nmi_injections                 0         0
nmi_window                     0         0
pf_fixed                   73983         0
pf_guest                    4027         0
remote_tlb_flush               1         0
request_irq                    6         0
signal_exits              135731         2
tlb_flush                  26760         0

qemu-kvm.git:

efer_reload                    0         0
exits                    8697244        33
fpu_reload                    46         0
halt_exits                   206         8
halt_wakeup                    7         0
host_state_reload         105173         8
hypercalls                     0         0
insn_emulation           6984118        21
insn_emulation_fail            0         0
invlpg                      9682         0
io_exits                  626201         0
irq_exits                  22930         4
irq_injections              2815         8
irq_window                  1029         0
largepages                     0         0
mmio_exits                  3657         0
mmu_cache_miss              5271         0
mmu_flooded                 2466         0
mmu_pde_zapped              1146         0
mmu_pte_updated             5294         0
mmu_pte_write             191173         0
mmu_recycled                   0         0
mmu_shadow_zapped           6405         0
mmu_unsync                    17         0
nmi_injections                 0         0
nmi_window                     0         0
pf_fixed                   73580         0
pf_guest                    4169         0
remote_tlb_flush               1         0
request_irq                    0         0
signal_exits               24873         0
tlb_flush                  26628         0

> 
> Maybe we're missing a coalesced io in qemu.git?  It's also possible that 
> gpxe is hitting the apic or pit quite a lot.
> 
> Regards,
> 
> Anthony Liguori
> 
> > Ideas?
> > --
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