From: Gleb Natapov <gleb@redhat.com>
To: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>,
Avi Kivity <avi.kivity@gmail.com>,
LKML <linux-kernel@vger.kernel.org>, KVM <kvm@vger.kernel.org>
Subject: Re: [PATCH v2 06/12] KVM: MMU: introduce a static table to map guest access to spte access
Date: Tue, 29 Jan 2013 15:16:51 +0200 [thread overview]
Message-ID: <20130129131651.GD15004@redhat.com> (raw)
In-Reply-To: <20130129010758.GA12132@amt.cnet>
On Mon, Jan 28, 2013 at 11:07:58PM -0200, Marcelo Tosatti wrote:
> On Mon, Jan 28, 2013 at 10:07:15PM -0200, Marcelo Tosatti wrote:
> > On Fri, Jan 25, 2013 at 10:46:31AM +0800, Xiao Guangrong wrote:
> > > On 01/25/2013 08:15 AM, Marcelo Tosatti wrote:
> > > > On Wed, Jan 23, 2013 at 06:07:20PM +0800, Xiao Guangrong wrote:
> > > >> It makes set_spte more clean and reduces branch prediction
> > > >>
> > > >> Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
> > > >> ---
> > > >> arch/x86/kvm/mmu.c | 37 ++++++++++++++++++++++++++-----------
> > > >> 1 files changed, 26 insertions(+), 11 deletions(-)
> > > >
> > > > Don't see set_spte as being a performance problem?
> > > > IMO the current code is quite simple.
> > >
> > > Yes, this is not a performance problem.
> > >
> > > I just dislike this many continuous "if"-s in the function:
> > >
> > > if (xxx)
> > > xxx
> > > if (xxx)
> > > xxx
> > > ....
> > >
> > > Totally, it has 7 "if"-s before this patch.
> > >
> > > Okay, if you think this is unnecessary, i will drop this patch. :)
> >
> > Yes, please (unless you can show set_spte is a performance problem).
>
> Same thing for spte fast drop: is it a performance problem?
>
I like spte fast drop because it gets rid of "goto restart" pattern.
for_each_spte_in_rmap_safe() can be the alternative.
> Please try to group changes into smaller, less controversial sets with
> a clear goal:
>
> - Debated performance improvement.
> - Cleanups (eg mmu_set_spte argument removal).
> - Bug fixes.
> - Performance improvements.
>
> Thanks.
--
Gleb.
next prev parent reply other threads:[~2013-01-29 13:16 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-23 10:04 [PATCH v2 01/12] KVM: MMU: lazily drop large spte Xiao Guangrong
2013-01-23 10:04 ` [PATCH v2 02/12] KVM: MMU: cleanup mapping-level Xiao Guangrong
2013-01-23 10:05 ` [PATCH v2 03/12] KVM: MMU: simplify mmu_set_spte Xiao Guangrong
2013-01-29 0:21 ` Marcelo Tosatti
2013-01-29 2:55 ` Xiao Guangrong
2013-01-29 21:53 ` Marcelo Tosatti
2013-01-30 3:22 ` Xiao Guangrong
2013-01-23 10:06 ` [PATCH v2 04/12] KVM: MMU: simplify set_spte Xiao Guangrong
2013-01-23 10:06 ` [PATCH v2 05/12] KVM: MMU: introduce vcpu_adjust_access Xiao Guangrong
2013-01-24 10:36 ` Gleb Natapov
2013-01-24 11:33 ` Xiao Guangrong
2013-01-23 10:07 ` [PATCH v2 06/12] KVM: MMU: introduce a static table to map guest access to spte access Xiao Guangrong
2013-01-25 0:15 ` Marcelo Tosatti
2013-01-25 2:46 ` Xiao Guangrong
2013-01-29 0:07 ` Marcelo Tosatti
2013-01-29 1:07 ` Marcelo Tosatti
2013-01-29 13:16 ` Gleb Natapov [this message]
2013-01-30 3:53 ` Xiao Guangrong
2013-01-23 10:07 ` [PATCH v2 07/12] KVM: MMU: remove pt_access in mmu_set_spte Xiao Guangrong
2013-01-23 10:08 ` [PATCH v2 08/12] KVM: MMU: cleanup __direct_map Xiao Guangrong
2013-01-23 10:09 ` [PATCH v2 09/12] KVM: MMU: introduce mmu_spte_establish Xiao Guangrong
2013-01-23 10:09 ` [PATCH v2 10/12] KVM: MMU: unify the code of walking pte list Xiao Guangrong
2013-01-27 13:28 ` Gleb Natapov
2013-01-29 3:01 ` Xiao Guangrong
2013-01-23 10:10 ` [PATCH v2 11/12] KVM: MMU: fix spte assertion Xiao Guangrong
2013-01-23 10:10 ` [PATCH v2 12/12] KVM: MMU: fast drop all spte on the pte_list Xiao Guangrong
2013-01-27 12:06 ` [PATCH v2 01/12] KVM: MMU: lazily drop large spte Gleb Natapov
2013-01-29 2:57 ` Xiao Guangrong
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