On 04/21/2013 11:24 PM, Marcelo Tosatti wrote: > 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? Hi Marcelo, I am worried about: ====== We can not release all rmaps. If we do this, ->invalidate_page and ->invalidate_range_start can not find any spte using the host page, that means, Accessed/Dirty for host page is missing tracked. (missing call kvm_set_pfn_accessed and kvm_set_pfn_dirty properly.) [https://lkml.org/lkml/2013/4/18/358] ====== Do you think this is a issue? What's your idea? Thanks! -- 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
