From: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
To: Avi Kivity <avi@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>,
LKML <linux-kernel@vger.kernel.org>, KVM <kvm@vger.kernel.org>
Subject: Re: [PATCH v2 10/16] KVM: MMU: fask check whether page is writable
Date: Tue, 17 Apr 2012 20:10:55 +0800 [thread overview]
Message-ID: <4F8D5DCF.1000702@linux.vnet.ibm.com> (raw)
In-Reply-To: <4F8D1EB5.2000302@redhat.com>
On 04/17/2012 03:41 PM, Avi Kivity wrote:
> On 04/17/2012 06:55 AM, Xiao Guangrong wrote:
>> On 04/16/2012 07:47 PM, Avi Kivity wrote:
>>
>>> On 04/16/2012 01:20 PM, Xiao Guangrong wrote:
>>>>>>
>>>>>> It is used to avoid the unnecessary overload
>>>>>
>>>>> It's overloading me :(
>>>>>
>>>>
>>>>
>>>> Sorry.
>>>>
>>>
>>> The trick is to send those in separate patchset so the maintainer
>>> doesn't notice.
>>>
>>
>>
>> Thanks for your suggestion, i will pay more attention on it in the
>> further.
>>
>> For this patch, what did you mean of "those"? You mean the whole
>> rmap.PTE_LIST_WP_BIT (fast check for shadow page table write protection
>> and host write protection) or just about host_page_write_protect
>> (for KSM only)?
>
> All of it. Let's start with just modifying sptes concurrently and only
> later add reading bits from rmap concurrently, if it proves necessary.
>
Okay, i agree.
>>
>> If we do not have rmap.PTE_LIST_WP_BIT, there may have regression on
>> shadow mmu.
>>
>> Hmm, do i need implement rmap.PTE_LIST_WP_BIT, then fast page fault?
>
> Let's try to measure the effect without rmap.PTE_LIST_WP_BIT. Usually
> PTE chains for page tables are short so the effect would be small. Of
> course we can't tell about all guest.
>
It is not about rmap's spte, it is about sp.sync write-protect, if the sp.sync
is written, the fast page fault path will be triggered even if no migration and
no framebuffer.
I have done a quick test for kernbench for 10 times and get the average value
without xwindow:
keep rmap.PTE_LIST_WP_BIT: 53.494
comment rmap.PTE_LIST_WP_BIT checking in page_fault_can_be_fast: 53.948
Anyway, for good review, let move fast page fault in first and discuss this in
the separate patchset later.
next prev parent reply other threads:[~2012-04-17 12:11 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-04-13 10:05 [PATCH v2 00/16] KVM: MMU: fast page fault Xiao Guangrong
2012-04-13 10:09 ` [PATCH v2 01/16] KVM: MMU: cleanup __direct_map Xiao Guangrong
2012-04-13 10:10 ` [PATCH v2 02/16] KVM: MMU: introduce mmu_spte_establish Xiao Guangrong
2012-04-13 10:10 ` [PATCH v2 03/16] KVM: MMU: properly assert spte on rmap walking path Xiao Guangrong
2012-04-14 2:15 ` Takuya Yoshikawa
2012-04-16 3:26 ` Xiao Guangrong
2012-04-13 10:11 ` [PATCH v2 04/16] KVM: MMU: return bool in __rmap_write_protect Xiao Guangrong
2012-04-14 2:00 ` Takuya Yoshikawa
2012-04-15 11:25 ` Avi Kivity
2012-04-16 14:14 ` Takuya Yoshikawa
2012-04-16 14:28 ` Avi Kivity
2012-04-16 15:54 ` Takuya Yoshikawa
2012-04-13 10:11 ` [PATCH v2 05/16] KVM: MMU: abstract spte write-protect Xiao Guangrong
2012-04-14 2:26 ` Takuya Yoshikawa
2012-04-16 3:27 ` Xiao Guangrong
2012-04-13 10:12 ` [PATCH v2 06/16] KVM: VMX: export PFEC.P bit on ept Xiao Guangrong
2012-04-13 10:12 ` [PATCH v2 07/16] KVM: MMU: introduce for_each_pte_list_spte Xiao Guangrong
2012-04-14 2:44 ` Takuya Yoshikawa
2012-04-16 3:36 ` Xiao Guangrong
2012-04-17 14:47 ` Takuya Yoshikawa
2012-04-18 4:01 ` Xiao Guangrong
2012-04-21 1:01 ` Takuya Yoshikawa
2012-04-21 4:36 ` Xiao Guangrong
2012-04-18 10:03 ` Xiao Guangrong
2012-04-21 1:03 ` Takuya Yoshikawa
2012-04-13 10:13 ` [PATCH v2 08/16] KVM: MMU: store more bits in rmap Xiao Guangrong
2012-04-13 10:13 ` [PATCH v2 09/16] KVM: MMU: fast mmu_need_write_protect path for hard mmu Xiao Guangrong
2012-04-13 10:14 ` [PATCH v2 10/16] KVM: MMU: fask check whether page is writable Xiao Guangrong
2012-04-14 3:01 ` Takuya Yoshikawa
2012-04-16 3:38 ` Xiao Guangrong
2012-04-15 15:16 ` Avi Kivity
2012-04-16 3:25 ` Xiao Guangrong
2012-04-16 10:02 ` Avi Kivity
2012-04-16 10:20 ` Xiao Guangrong
2012-04-16 11:47 ` Avi Kivity
2012-04-17 3:55 ` Xiao Guangrong
2012-04-17 7:41 ` Avi Kivity
2012-04-17 12:10 ` Xiao Guangrong [this message]
2012-04-13 10:14 ` [PATCH v2 11/16] KVM: MMU: introduce SPTE_ALLOW_WRITE bit Xiao Guangrong
2012-04-13 10:15 ` [PATCH v2 12/16] KVM: MMU: introduce SPTE_WRITE_PROTECT bit Xiao Guangrong
2012-04-13 10:15 ` [PATCH v2 13/16] KVM: MMU: break sptes write-protect if gfn is writable Xiao Guangrong
2012-04-13 10:16 ` [PATCH v2 14/16] KVM: MMU: fast path of handling guest page fault Xiao Guangrong
2012-04-18 1:47 ` Marcelo Tosatti
2012-04-18 3:53 ` Xiao Guangrong
2012-04-18 23:08 ` Marcelo Tosatti
2012-04-13 10:17 ` [PATCH v2 15/16] KVM: MMU: trace fast " Xiao Guangrong
2012-04-13 10:17 ` [PATCH v2 16/16] KVM: MMU: fix kvm_mmu_pagetable_walk tracepoint Xiao Guangrong
2012-04-14 3:37 ` [PATCH v2 00/16] KVM: MMU: fast page fault Takuya Yoshikawa
2012-04-16 3:50 ` Xiao Guangrong
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