RE: [Xen-ia64-devel] [PATCH] XEN: accelerate guest tr search.

["Xu, Anthony" <anthony.xu@xxxxxxxxx>]

>From: Magenheimer, Dan (HP Labs Fort Collins) 
>Sent: 2006年3月3日 1:52
>I have a couple of concerns with this patch:
>
>1) Because of vcpu_quick_region_check() this patch will
>   matter (on Linux) only for code/data in region 7 that
>   is not pinned by a guest TR.  Vcpu_quick_region_check() avoids
>   checking the guest TRs if accessing a region that has no TRs
>   set (e.g. on Linux, the vast majority of misses will never
>   check any of the guest TRs).
Agree, vcpu_quick_region_check is a good approach, I'll introduce it into 
vti-domain, yes, it can filter majority of tlb misses.

>2) The code assumes that a guest utilizes the TRs in order
>   with no holes (e.g. TR0-3 rather than TR0,2,4,6).  This
>   is true for Linux but if we are going to add this performance
>   shortcut, it might as well be more robust.
Agree, this patch seems to be linux-specifical, Maybe bitmap is a 
better approach, which is OS-independent.

>3) I think we should be very careful about making changes
>   that are intended to improve performance without doing any
>   benchmarking.  Many times I have seen code that was intended
>   to improve performance actually -- surprise! -- result in
>   performance degradation.
Agree, but it's unpractical to let developer to do benchmark testing,
Since Fujitsu will deliver regular performance reports, I think we could
depend on these reports to find out the patch which cause performance 
degradation.


Thanks,
Anthony

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