From: Paolo Bonzini <pbonzini@redhat.com>
To: Gleb Natapov <gleb@redhat.com>
Cc: Brian Rak <brak@gameservers.com>, kvm@vger.kernel.org
Subject: Re: Windows Server 2008R2 KVM guest performance issues
Date: Tue, 27 Aug 2013 10:38:04 +0200 [thread overview]
Message-ID: <521C656C.9090208@redhat.com> (raw)
In-Reply-To: <20130827073833.GD22899@redhat.com>
Il 27/08/2013 09:38, Gleb Natapov ha scritto:
> On Tue, Aug 27, 2013 at 09:18:00AM +0200, Paolo Bonzini wrote:
>>> I've captured 20,000 lines of kvm trace output. This can be found
>>> https://gist.github.com/devicenull/fa8f49d4366060029ee4/raw/fb89720d34b43920be22e3e9a1d88962bf305da8/trace
>>
>> The guest is doing quite a lot of exits per second, mostly to (a) access
>> the ACPI timer
> I see a lot of PM timer access not ACPI timer. The solution for that is
> the patchset Brian linked.
ACPI timer = PM timer, no?
>> (b) service NMIs. In fact, every NMI is reading the
>> timer too and causing an exit to QEMU.
>>
> Do you mean "kvm_exit: reason EXCEPTION_NMI rip 0xfffff800016dcf84 info
> 0 80000307"? Those are not NMIs, single NMI will kill Windows, they are #NM
> exceptions.
Oops, yes.
> Brian, is your workload uses floating point calculation?
Yeah, it looks like it does, there are a lot of kvm_fpu tracepoints too.
Basically the problem is that every exit to userspace unloads the FPU in
vcpu_put.
qemu-system-x86-16189 [003] d... 9439.144500: kvm_entry: vcpu 12
qemu-system-x86-16189 [003] d... 9439.144502: kvm_exit: reason EXCEPTION_NMI rip 0xfffff800016dcf84 info 0 80000307
qemu-system-x86-16189 [003] .... 9439.144502: kvm_fpu: load
qemu-system-x86-16189 [003] d... 9439.144503: kvm_entry: vcpu 12
qemu-system-x86-16189 [003] d... 9439.144505: kvm_exit: reason IO_INSTRUCTION rip 0xfffff8000162d17d info b008000b 0
qemu-system-x86-16189 [003] .... 9439.144506: kvm_emulate_insn: 0:fffff8000162d17d:ed (prot64)
qemu-system-x86-16189 [003] .... 9439.144506: kvm_pio: pio_read at 0xb008 size 4 count 1
qemu-system-x86-16189 [003] .... 9439.144507: kvm_userspace_exit: reason KVM_EXIT_IO (2)
qemu-system-x86-16189 [003] .... 9439.144508: kvm_fpu: unload
qemu-system-x86-16189 [003] d... 9439.144578: kvm_entry: vcpu 12
qemu-system-x86-16189 [003] d... 9439.144579: kvm_exit: reason EXCEPTION_NMI rip 0xfffff800016dcf84 info 0 80000307
qemu-system-x86-16189 [003] .... 9439.144581: kvm_fpu: load
qemu-system-x86-16189 [003] d... 9439.144581: kvm_entry: vcpu 12
qemu-system-x86-16189 [003] d... 9439.144583: kvm_exit: reason IO_INSTRUCTION rip 0xfffff8000162d17d info b008000b 0
qemu-system-x86-16189 [003] .... 9439.144585: kvm_emulate_insn: 0:fffff8000162d17d:ed (prot64)
qemu-system-x86-16189 [003] .... 9439.144585: kvm_pio: pio_read at 0xb008 size 4 count 1
qemu-system-x86-16189 [003] .... 9439.144586: kvm_userspace_exit: reason KVM_EXIT_IO (2)
qemu-system-x86-16189 [003] .... 9439.144587: kvm_fpu: unload
qemu-system-x86-16189 [003] d... 9439.144787: kvm_entry: vcpu 12
qemu-system-x86-16189 [003] d... 9439.144788: kvm_exit: reason EXCEPTION_NMI rip 0xfffff800016dcf84 info 0 80000307
qemu-system-x86-16189 [003] .... 9439.144789: kvm_fpu: load
qemu-system-x86-16189 [003] d... 9439.144789: kvm_entry: vcpu 12
qemu-system-x86-16189 [003] d... 9439.144791: kvm_exit: reason IO_INSTRUCTION rip 0xfffff8000162d17d info b008000b 0
qemu-system-x86-16189 [003] .... 9439.144792: kvm_emulate_insn: 0:fffff8000162d17d:ed (prot64)
qemu-system-x86-16189 [003] .... 9439.144793: kvm_pio: pio_read at 0xb008 size 4 count 1
qemu-system-x86-16189 [003] .... 9439.144794: kvm_userspace_exit: reason KVM_EXIT_IO (2)
qemu-system-x86-16189 [003] .... 9439.144794: kvm_fpu: unload
It should be interesting to analyze the cost in kvm-unit-tests. I'll look
at it.
Paolo
next prev parent reply other threads:[~2013-08-27 8:38 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-26 19:15 Windows Server 2008R2 KVM guest performance issues Brian Rak
2013-08-26 22:01 ` Brian Rak
2013-08-27 7:18 ` Paolo Bonzini
2013-08-27 7:38 ` Gleb Natapov
2013-08-27 8:38 ` Paolo Bonzini [this message]
2013-08-27 8:44 ` Gleb Natapov
2013-08-27 14:09 ` Brian Rak
2013-08-27 14:44 ` Brian Rak
2013-08-27 15:09 ` Paolo Bonzini
2013-08-27 16:45 ` Brian Rak
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