From: Marcelo Tosatti <mtosatti@redhat.com>
To: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Cc: Gleb Natapov <gleb@redhat.com>,
avi.kivity@gmail.com, linux-kernel@vger.kernel.org,
kvm@vger.kernel.org
Subject: Re: [PATCH v3 00/15] KVM: MMU: fast zap all shadow pages
Date: Sun, 21 Apr 2013 12:24:31 -0300 [thread overview]
Message-ID: <20130421152431.GA28437@amt.cnet> (raw)
In-Reply-To: <5173F319.2040106@linux.vnet.ibm.com>
On Sun, Apr 21, 2013 at 10:09:29PM +0800, Xiao Guangrong wrote:
> On 04/21/2013 09:03 PM, Gleb Natapov wrote:
> > On Tue, Apr 16, 2013 at 02:32:38PM +0800, Xiao Guangrong wrote:
> >> This patchset is based on my previous two patchset:
> >> [PATCH 0/2] KVM: x86: avoid potential soft lockup and unneeded mmu reload
> >> (https://lkml.org/lkml/2013/4/1/2)
> >>
> >> [PATCH v2 0/6] KVM: MMU: fast invalid all mmio sptes
> >> (https://lkml.org/lkml/2013/4/1/134)
> >>
> >> Changlog:
> >> V3:
> >> completely redesign the algorithm, please see below.
> >>
> > This looks pretty complicated. Is it still needed in order to avoid soft
> > lockups after "avoid potential soft lockup and unneeded mmu reload" patch?
>
> Yes.
>
> I discussed this point with Marcelo:
>
> ======
> BTW, to my honest, i do not think spin_needbreak is a good way - it does
> not fix the hot-lock contention and it just occupies more cpu time to avoid
> possible soft lock-ups.
>
> Especially, zap-all-shadow-pages can let other vcpus fault and vcpus contest
> mmu-lock, then zap-all-shadow-pages release mmu-lock and wait, other vcpus
> create page tables again. zap-all-shadow-page need long time to be finished,
> the worst case is, it can not completed forever on intensive vcpu and memory
> usage.
>
> I still think the right way to fix this kind of thing is optimization for
> mmu-lock.
> ======
>
> Which parts scare you? Let's find a way to optimize for it. ;). For example,
> if you do not like unmap_memslot_rmap_nolock(), we can simplify it - We can
> use walk_shadow_page_lockless_begin() and walk_shadow_page_lockless_end() to
> protect spte instead of kvm->being_unmaped_rmap.
>
> Thanks!
Xiao,
You can just remove all shadow rmaps now that you've agreed per-memslot
flushes are not necessary. Which then gets rid of necessity for lockless
rmap accesses. Right?
next prev parent reply other threads:[~2013-04-21 15:24 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-04-16 6:32 [PATCH v3 00/15] KVM: MMU: fast zap all shadow pages Xiao Guangrong
2013-04-16 6:32 ` [PATCH v3 01/15] KVM: x86: clean up and optimize for kvm_arch_free_memslot Xiao Guangrong
2013-04-16 6:32 ` [PATCH v3 02/15] KVM: fold kvm_arch_create_memslot into kvm_arch_prepare_memory_region Xiao Guangrong
2013-04-16 6:32 ` [PATCH v3 03/15] KVM: x86: do not reuse rmap when memslot is moved Xiao Guangrong
2013-04-16 6:32 ` [PATCH v3 04/15] KVM: MMU: abstract memslot rmap related operations Xiao Guangrong
2013-04-16 6:32 ` [PATCH v3 05/15] KVM: MMU: allow per-rmap operations Xiao Guangrong
2013-04-16 6:32 ` [PATCH v3 06/15] KVM: MMU: allow concurrently clearing spte on remove-only pte-list Xiao Guangrong
2013-04-16 6:32 ` [PATCH v3 07/15] KVM: MMU: introduce invalid rmap handlers Xiao Guangrong
2013-04-17 23:38 ` Marcelo Tosatti
2013-04-18 3:15 ` Xiao Guangrong
2013-04-16 6:32 ` [PATCH v3 08/15] KVM: MMU: allow unmap invalid rmap out of mmu-lock Xiao Guangrong
2013-04-18 11:00 ` Gleb Natapov
2013-04-18 11:22 ` Xiao Guangrong
2013-04-18 11:38 ` Gleb Natapov
2013-04-18 12:10 ` Xiao Guangrong
2013-04-16 6:32 ` [PATCH v3 09/15] KVM: MMU: introduce free_meslot_rmap_desc_nolock Xiao Guangrong
2013-04-16 6:32 ` [PATCH v3 10/15] KVM: x86: introduce memslot_set_lpage_disallowed Xiao Guangrong
2013-04-16 6:32 ` [PATCH v3 11/15] KVM: MMU: introduce kvm_clear_all_lpage_info Xiao Guangrong
2013-04-16 6:32 ` [PATCH v3 12/15] KVM: MMU: fast invalid all shadow pages Xiao Guangrong
2013-04-18 0:05 ` Marcelo Tosatti
2013-04-18 4:00 ` Xiao Guangrong
2013-04-18 13:03 ` Marcelo Tosatti
2013-04-18 13:29 ` Marcelo Tosatti
2013-04-18 15:20 ` Xiao Guangrong
2013-04-16 6:32 ` [PATCH v3 13/15] KVM: x86: use the fast way to invalid all pages Xiao Guangrong
2013-04-16 6:32 ` [PATCH v3 14/15] KVM: move srcu_read_lock/srcu_read_unlock to arch-specified code Xiao Guangrong
2013-04-16 6:32 ` [PATCH v3 15/15] KVM: MMU: replace kvm_zap_all with kvm_mmu_invalid_all_pages Xiao Guangrong
2013-04-18 0:08 ` Marcelo Tosatti
2013-04-18 4:03 ` Xiao Guangrong
2013-04-20 17:18 ` Marcelo Tosatti
2013-04-21 6:59 ` Xiao Guangrong
2013-04-21 13:03 ` [PATCH v3 00/15] KVM: MMU: fast zap all shadow pages Gleb Natapov
2013-04-21 14:09 ` Xiao Guangrong
2013-04-21 15:24 ` Marcelo Tosatti [this message]
2013-04-22 2:50 ` Xiao Guangrong
2013-04-22 9:21 ` Gleb Natapov
2013-04-23 0:19 ` Xiao Guangrong
2013-04-23 6:28 ` Gleb Natapov
2013-04-23 7:20 ` Xiao Guangrong
2013-04-23 7:33 ` Gleb Natapov
2013-04-21 15:27 ` Marcelo Tosatti
2013-04-21 15:35 ` Marcelo Tosatti
2013-04-22 12:39 ` Gleb Natapov
2013-04-22 13:45 ` Takuya Yoshikawa
2013-04-22 23:02 ` Marcelo Tosatti
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