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? -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
