Just verified that the performance issue has already been fixed on KVM-32.
Thanks
Yunfeng
>-----Original Message-----
>From: Avi Kivity [mailto:[EMAIL PROTECTED]
>Sent: 2007年7月24日 0:12
>To: Zhao, Yunfeng
>Cc: kvm-devel@lists.sourceforge.net
>Subject: Re: [kvm-devel] ABAT Testing report, kernel 76f0301b5.., user
>04cff0e47..
>
>Zhao, Yunfeng wrote:
>> Hi, all
>>
>> This is today's ABAT testing result against kvm.git
>76f0301b5e4d2603d8e1ee5295db29faea660b49 and kvm-userspace.git
>04cff0e47c4cc1e3d51f917a657b97ac2ed29719
>> We are still using UP guests in the testing, we will try to enable some SMP
>Windows and Linux tests in this week.
>>
>> One new issue is about performance regression since KVM-29
>> 1. Performance regression since KVM-29
>>
>https://sourceforge.net/tracker/index.php?func=detail&aid=1758756&group_id=
>180599&atid=893831
>>
>>
>
>I bisected this to
>
>commit 8a1449563b3e5ede56b28cc977c8da22a17cdf51
>Author: Luca Tettamanti <[EMAIL PROTECTED]>
>Date: Tue Jun 19 22:41:38 2007 +0200
>
> KVM: Avoid useless memory write when possible
>
> When writing to normal memory and the memory area is unchanged the write
> can be safely skipped, avoiding the costly kvm_mmu_pte_write.
>
> Signed-Off-By: Luca Tettamanti <[EMAIL PROTECTED]>
> Signed-off-by: Avi Kivity <[EMAIL PROTECTED]>
>
>diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
>index 7826f16..5603000 100644
>--- a/drivers/kvm/kvm_main.c
>+++ b/drivers/kvm/kvm_main.c
>@@ -1170,8 +1170,10 @@ static int emulator_write_phys(struct kvm_vcpu
>*vcpu, gpa_t gpa,
> return 0;
> mark_page_dirty(vcpu->kvm, gpa >> PAGE_SHIFT);
> virt = kmap_atomic(page, KM_USER0);
>- kvm_mmu_pte_write(vcpu, gpa, virt + offset, val, bytes);
>- memcpy(virt + offset_in_page(gpa), val, bytes);
>+ if (memcmp(virt + offset_in_page(gpa), val, bytes)) {
>+ kvm_mmu_pte_write(vcpu, gpa, virt + offset, val, bytes);
>+ memcpy(virt + offset_in_page(gpa), val, bytes);
>+ }
> kunmap_atomic(virt, KM_USER0);
> return 1;
> }
>
>The effect with this patch applied is that pf_fixed grows very high.
>I'm guessing that this is because not calling kvm_mmu_pte_write()
>defeats the fork detector and causes a high amount of emulated writes to
>page table when fork() resets the writable bit on read-only ptes.
>
>--
>error compiling committee.c: too many arguments to function
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