Messages in this thread | | | Date | Thu, 3 May 2012 09:15:58 +0900 | From | Takuya Yoshikawa <> | Subject | Re: [PATCH v4 06/10] KVM: MMU: fast path of handling guest page fault |
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On Wed, 02 May 2012 13:39:51 +0800 Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> wrote:
> > Was the problem really mmu_lock contention?
> Takuya, i am so tired to argue the advantage of lockless write-protect > and lockless O(1) dirty-log again and again.
You are missing my point. Please do not take my comments as an objection to your whole work: whey do you feel so?
I thought that your new fast-page-fault path was fast and optimized the guest during dirty logging.
So in this v4, you might get a similar result even before dropping mmu_lock, without 07/10?, if the problem Marcelo explained was not there.
Of course there is a problem of mmu_lock contention. What I am suggesting is to split that problem and do measurement separately so that part of your work can be merged soon.
Your guest size and workload was small to make get_dirty hold mmu_lock long time. If you want to appeal the real value of lock-less, you need to do another measurment.
But this is your work and it's up to you. Although I was thinking to help your measurement, I cannot do that knowing the fact that you would not welcome my help.
> > Although I am not certain about what will be really needed in the > > final form, if this kind of maybe-needed-overhead is going to be > > added little by little, I worry about possible regression.
> Well, will you suggest Linus to reject all patches and stop > all discussion for the "possible regression" reason?
My concern was for Marcelo's examples, not your current implementation. If you can show explicitely what will be needed in the final form, I do not have any concern.
Sorry for disturbing.
Thanks, Takuya
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