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From: Marcelo Tosatti <mtosatti@redhat.com>
To: Gleb Natapov <gleb@redhat.com>
Cc: Avi Kivity <avi.kivity@gmail.com>,
	Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>,
	"pbonzini@redhat.com Bonzini" <pbonzini@redhat.com>,
	linux-kernel@vger.kernel.org, kvm <kvm@vger.kernel.org>,
	Eric Dumazet <dada1@cosmosbay.com>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v3 07/15] KVM: MMU: introduce nulls desc
Date: Mon, 25 Nov 2013 16:06:56 -0200	[thread overview]
Message-ID: <20131125180656.GA21858@amt.cnet> (raw)
In-Reply-To: <20131125142928.GD959@redhat.com>

GOn Mon, Nov 25, 2013 at 04:29:28PM +0200, Gleb Natapov wrote:
> On Mon, Nov 25, 2013 at 12:23:51PM -0200, Marcelo Tosatti wrote:
> > On Mon, Nov 25, 2013 at 02:48:37PM +0200, Avi Kivity wrote:
> > > On Mon, Nov 25, 2013 at 8:11 AM, Xiao Guangrong
> > > <xiaoguangrong@linux.vnet.ibm.com> wrote:
> > > >
> > > > On Nov 23, 2013, at 3:14 AM, Marcelo Tosatti <mtosatti@redhat.com> wrote:
> > > 
> > > <snip complicated stuff about parent_pte>
> > > 
> > > I'm not really following, but note that parent_pte predates EPT (and
> > > the use of rcu in kvm), so all the complexity that is the result of
> > > trying to pack as many list entries into a cache line can be dropped.
> > > Most setups now would have exactly one list entry, which is handled
> > > specially antyway.
> > > 
> > > Alternatively, the trick of storing multiple entries in one list entry
> > > can be moved to generic code, it may be useful to others.
> > 
> > Yes, can the lockless list walking code be transformed into generic
> > single-linked list walking? So the correctness can be verified
> > independently, and KVM becomes a simple user of that interface.
> > 
> The code will become simpler but the problem of never ending walk of
> rculist_nulls will remain.

Yes. Hopefully it can be fixed in some way.

> > The simpler version is to maintain lockless walk on depth-1 rmap entries
> > (and grab the lock once depth-2 entry is found).
> And release it between each rmap walk or at the very end of write
> protect?

Or keep it locked until 10 consecutive sptes with depth 1 are found.


  reply	other threads:[~2013-11-25 18:14 UTC|newest]

Thread overview: 69+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-10-23 13:29 [PATCH v3 00/15] KVM: MMU: locklessly write-protect Xiao Guangrong
2013-10-23 13:29 ` [PATCH v3 01/15] KVM: MMU: properly check last spte in fast_page_fault() Xiao Guangrong
2013-11-12  0:25   ` Marcelo Tosatti
2013-10-23 13:29 ` [PATCH v3 02/15] KVM: MMU: lazily drop large spte Xiao Guangrong
2013-11-12 22:44   ` Marcelo Tosatti
2013-10-23 13:29 ` [PATCH v3 03/15] KVM: MMU: flush tlb if the spte can be locklessly modified Xiao Guangrong
2013-11-13  0:10   ` Marcelo Tosatti
2013-10-23 13:29 ` [PATCH v3 04/15] KVM: MMU: flush tlb out of mmu lock when write-protect the sptes Xiao Guangrong
2013-11-14  0:36   ` Marcelo Tosatti
2013-11-14  5:15     ` Xiao Guangrong
2013-11-14 18:39       ` Marcelo Tosatti
2013-11-15  7:09         ` Xiao Guangrong
2013-11-19  0:19           ` Marcelo Tosatti
2013-10-23 13:29 ` [PATCH v3 05/15] KVM: MMU: update spte and add it into rmap before dirty log Xiao Guangrong
2013-11-15  0:08   ` Marcelo Tosatti
2013-10-23 13:29 ` [PATCH v3 06/15] KVM: MMU: redesign the algorithm of pte_list Xiao Guangrong
2013-11-19  0:48   ` Marcelo Tosatti
2013-10-23 13:29 ` [PATCH v3 07/15] KVM: MMU: introduce nulls desc Xiao Guangrong
2013-11-22 19:14   ` Marcelo Tosatti
2013-11-25  6:11     ` Xiao Guangrong
2013-11-25  6:29       ` Xiao Guangrong
2013-11-25 18:12         ` Marcelo Tosatti
2013-11-26  3:21           ` Xiao Guangrong
2013-11-26 10:12             ` Gleb Natapov
2013-11-26 19:31             ` Marcelo Tosatti
2013-11-28  8:53               ` Xiao Guangrong
2013-12-03  7:10                 ` Xiao Guangrong
2013-12-05 13:50                   ` Marcelo Tosatti
2013-12-05 15:30                     ` Xiao Guangrong
2013-12-06  0:15                       ` Marcelo Tosatti
2013-12-06  0:22                       ` Marcelo Tosatti
2013-12-10  6:58                         ` Xiao Guangrong
2013-11-25 10:19       ` Gleb Natapov
2013-11-25 10:25         ` Xiao Guangrong
2013-11-25 12:48       ` Avi Kivity
2013-11-25 14:23         ` Marcelo Tosatti
2013-11-25 14:29           ` Gleb Natapov
2013-11-25 18:06             ` Marcelo Tosatti [this message]
2013-11-26  3:10           ` Xiao Guangrong
2013-11-26 10:15             ` Gleb Natapov
2013-11-26 19:58             ` Marcelo Tosatti
2013-11-28  8:32               ` Xiao Guangrong
2013-11-25 14:08       ` Marcelo Tosatti
2013-11-26  3:02         ` Xiao Guangrong
2013-11-25  9:31     ` Peter Zijlstra
2013-11-25 10:59       ` Xiao Guangrong
2013-11-25 11:05         ` Peter Zijlstra
2013-11-25 11:29           ` Peter Zijlstra
2013-10-23 13:29 ` [PATCH v3 08/15] KVM: MMU: introduce pte-list lockless walker Xiao Guangrong
2013-10-23 13:29 ` [PATCH v3 09/15] KVM: MMU: initialize the pointers in pte_list_desc properly Xiao Guangrong
2013-10-23 13:29 ` [PATCH v3 10/15] KVM: MMU: allocate shadow pages from slab Xiao Guangrong
2013-10-24  9:19   ` Gleb Natapov
2013-10-24  9:29     ` Xiao Guangrong
2013-10-24  9:52       ` Gleb Natapov
2013-10-24 10:10         ` Xiao Guangrong
2013-10-24 10:39           ` Gleb Natapov
2013-10-24 11:01             ` Xiao Guangrong
2013-10-24 12:32               ` Gleb Natapov
2013-10-28  3:16                 ` Xiao Guangrong
2013-10-23 13:29 ` [PATCH v3 11/15] KVM: MMU: locklessly access shadow page under rcu protection Xiao Guangrong
2013-10-23 13:29 ` [PATCH v3 12/15] KVM: MMU: check last spte with unawareness of mapping level Xiao Guangrong
2013-10-23 13:29 ` [PATCH v3 13/15] KVM: MMU: locklessly write-protect the page Xiao Guangrong
2013-10-24  9:17   ` Gleb Natapov
2013-10-24  9:24     ` Xiao Guangrong
2013-10-24  9:32       ` Gleb Natapov
2013-10-23 13:29 ` [PATCH v3 14/15] KVM: MMU: clean up spte_write_protect Xiao Guangrong
2013-10-23 13:29 ` [PATCH v3 15/15] KVM: MMU: use rcu functions to access the pointer Xiao Guangrong
2013-11-03 12:29 ` [PATCH v3 00/15] KVM: MMU: locklessly write-protect Gleb Natapov
2013-11-11  5:33   ` Xiao Guangrong

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