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Date: Fri, 06 Jul 2012 15:17:53 +0530
From: Nikunj A Dadhania <nikunj@...ux.vnet.ibm.com>
To: Marcelo Tosatti <mtosatti@...hat.com>
Cc: peterz@...radead.org, mingo@...e.hu, avi@...hat.com,
raghukt@...ux.vnet.ibm.com, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org, x86@...nel.org, jeremy@...p.org,
vatsa@...ux.vnet.ibm.com, hpa@...or.com
Subject: Re: [PATCH v2 3/7] KVM: Add paravirt kvm_flush_tlb_others
On Tue, 3 Jul 2012 04:55:35 -0300, Marcelo Tosatti <mtosatti@...hat.com> wrote:
> On Mon, Jun 04, 2012 at 10:37:24AM +0530, Nikunj A. Dadhania wrote:
> > flush_tlb_others_ipi depends on lot of statics in tlb.c. Replicated
> > the flush_tlb_others_ipi as kvm_flush_tlb_others to further adapt to
> > paravirtualization.
> >
> > Use the vcpu state information inside the kvm_flush_tlb_others to
> > avoid sending ipi to pre-empted vcpus.
> >
> > * Do not send ipi's to offline vcpus and set flush_on_enter flag
> > * For online vcpus: Wait for them to clear the flag
> >
> > The approach was discussed here: https://lkml.org/lkml/2012/2/20/157
> >
> > Suggested-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > Signed-off-by: Nikunj A. Dadhania <nikunj@...ux.vnet.ibm.com>
> >
> > --
> > Pseudo Algo:
> >
> > Write()
> > ======
> >
> > guest_exit()
> > flush_on_enter[i]=0;
> > running[i] = 0;
> >
> > guest_enter()
> > running[i] = 1;
> > smp_mb();
> > if(flush_on_enter[i]) {
> > tlb_flush()
> > flush_on_enter[i]=0;
> > }
> >
> >
> > Read()
> > ======
> >
> > GUEST KVM-HV
> >
> > f->flushcpumask = cpumask - me;
> >
> > again:
> > for_each_cpu(i, f->flushmask) {
> >
> > if (!running[i]) {
> > case 1:
> >
> > running[n]=1
> >
> > (cpuN does not see
> > flush_on_enter set,
> > guest later finds it
> > running and sends ipi,
> > we are fine here, need
> > to clear the flag on
> > guest_exit)
> >
> > flush_on_enter[i] = 1;
> > case2:
> >
> > running[n]=1
> > (cpuN - will see flush
> > on enter and an IPI as
> > well - addressed in patch-4)
> >
> > if (!running[i])
> > cpu_clear(f->flushmask); All is well, vm_enter
> > will do the fixup
> > }
> > case 3:
> > running[n] = 0;
> >
> > (cpuN went to sleep,
> > we saw it as awake,
> > ipi sent, but wait
> > will break without
> > zero_mask and goto
> > again will take care)
> >
> > }
> > send_ipi(f->flushmask)
> >
> > wait_a_while_for_zero_mask();
> >
> > if (!zero_mask)
> > goto again;
>
> Can you please measure increased vmentry/vmexit overhead? x86/vmexit.c
> of git://git.kernel.org/pub/scm/virt/kvm/kvm-unit-tests.git should
> help.
>
Please find below the results (debug patch attached for enabling
registration of kvm_vcu_state)
I have taken results for 1 and 4 vcpus. Used the following command for
starting the tests:
/usr/libexec/qemu-kvm -smp $i -device testdev,chardev=testlog -chardev
file,id=testlog,path=vmexit.out -serial stdio -kernel ./x86/vmexit.flat
Machine : IBM xSeries with Intel(R) Xeon(R) X7560 2.27GHz CPU
with 32 core, 32 online cpus and 4*64GB RAM.
x base - unpatched host kernel
+ wo_vs - patched host kernel, vcpu_state not registered
* w_vs.txt - patched host kernel and vcpu_state registered
1 vcpu results:
---------------
cpuid
=====
N Avg Stddev
x 10 2135.1 17.8975
+ 10 2188 18.3666
* 10 2448.9 43.9910
vmcall
======
N Avg Stddev
x 10 2025.5 38.1641
+ 10 2047.5 24.8205
* 10 2306.2 40.3066
mov_from_cr8
============
N Avg Stddev
x 10 12 0.0000
+ 10 12 0.0000
* 10 12 0.0000
mov_to_cr8
==========
N Avg Stddev
x 10 19.4 0.5164
+ 10 19.1 0.3162
* 10 19.2 0.4216
inl_from_pmtimer
================
N Avg Stddev
x 10 18093.2 462.0543
+ 10 16579.7 1448.8892
* 10 18577.7 266.2676
ple-round-robin
===============
N Avg Stddev
x 10 16.1 0.3162
+ 10 16.2 0.4216
* 10 15.3 0.4830
4 vcpus result
--------------
cpuid
=====
N Avg Stddev
x 10 2135.8 10.0642
+ 10 2165 6.4118
* 10 2423.7 12.5526
vmcall
======
N Avg Stddev
x 10 2028.3 19.6641
+ 10 2024.7 7.2273
* 10 2276.1 13.8680
mov_from_cr8
============
N Avg Stddev
x 10 12 0.0000
+ 10 12 0.0000
* 10 12 0.0000
mov_to_cr8
==========
N Avg Stddev
x 10 19 0.0000
+ 10 19 0.0000
* 10 19 0.0000
inl_from_pmtimer
================
N Avg Stddev
x 10 25574.2 1693.5374
+ 10 25190.7 2219.9223
* 10 23044 1230.8737
ipi
===
N Avg Stddev
x 20 31996.75 7290.1777
+ 20 33683.25 9795.1601
* 20 34563.5 8338.7826
ple-round-robin
===============
N Avg Stddev
x 10 6281.7 1543.8601
+ 10 6149.8 1207.7928
* 10 6433.3 2304.5377
Thanks
Nikunj
View attachment "enable_vcpu_state.diff" of type "text/x-patch" (1896 bytes)
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