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Re: [Xen-devel] Xen 4.3 development update



On 03/04/13 08:27, Jan Beulich wrote:
On 02.04.13 at 18:34, Tim Deegan <tim@xxxxxxx> wrote:
At 16:42 +0100 on 02 Apr (1364920927), Jan Beulich wrote:
On 02.04.13 at 16:07, George Dunlap <George.Dunlap@xxxxxxxxxxxxx> wrote:
* AMD NPT performance regression after c/s 24770:7f79475d3de7
   owner: ?
   Reference: http://marc.info/?l=xen-devel&m=135075376805215
This is supposedly fixed with the RTC changes Tim committed the
other day. Suravee, is that correct?
This is a separate problem.  IIRC the AMD XP perf issue is caused by the
emulation of LAPIC TPR accesses slowing down with Andres's p2m locking
patches.  XP doesn't have 'lazy IRQL' or support for CR8, so it takes a
_lot_ of vmexits for IRQL reads and writes.
Ah, okay, sorry for mixing this up. But how is this a regression
then?

My sense, when I looked at this back whenever that there was much more to this. The XP IRQL updating is a problem, but it's made terribly worse by the changset in question. It seemed to me like the kind of thing that would be caused by TLB or caches suddenly becoming much less effective.

 -George

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