Re: [tip:x86/urgent] x86, mm: Patch out arch_flush_lazy_mmu_mode()when running on bare metal

From: Konrad Rzeszutek Wilk
Date: Thu Apr 11 2013 - 11:43:14 EST

I am sorry for top posting. Haven't figured out how to reply inline in the Android email client.

Boris, could you repost it please? If I recall correctly the only question on that patch was whether to put stable@xxxxxxxxxxxxxxx on it and it was decided (by Greg) that was OK.

It is not an urgent patch though as it is only exposed with debug kernels.

Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> wrote:

>On 04/10/2013 08:30 PM, tip-bot for Boris Ostrovsky wrote:
>> Commit-ID: 511ba86e1d386f671084b5d0e6f110bb30b8eeb2
>> Gitweb:
>> Author: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
>> AuthorDate: Sat, 23 Mar 2013 09:36:36 -0400
>> Committer: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
>> CommitDate: Wed, 10 Apr 2013 11:25:10 -0700
>> x86, mm: Patch out arch_flush_lazy_mmu_mode() when running on bare metal
>> Invoking arch_flush_lazy_mmu_mode() results in calls to
>> preempt_enable()/disable() which may have performance impact.
>> Since lazy MMU is not used on bare metal we can patch away
>> arch_flush_lazy_mmu_mode() so that it is never called in such
>> environment.
>> [ hpa: the previous patch "Fix vmalloc_fault oops during lazy MMU
>> updates" may cause a minor performance regression on
>> bare metal. This patch resolves that performance regression. It is
>> somewhat unclear to me if this is a good -stable candidate. ]
>I think this
>was also part of lazy mmu set of patches but is missing in the latest
>batch of
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