[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] Re: performance regression from c/s 21647:cfba1560054a
Hi Jan, On a personal note, thanks for asking me about shadow pagetables, I've been missing this kind of fun and it's a good way to celebrate my return to Xen (and Citrix) after exactly two years... :-) Stefano imported an old patch of mine, so I am the culprit for this. On Thu, Nov 10, 2011 at 3:23 AM, Jan Beulich <JBeulich@xxxxxxxx> wrote: > in this c/s you did, besides the main purpose of the change, an > adjustment to check_for_early_unshadow() in that L2...L4 entries > would no longer be attempted to get unshadowed. Neither the > patch description nor the added comment really make clear why > this was done, and we now got a customer report regarding this > causing considerable slowdown in process creation/destruction > intensive workloads (e.g. shell scripts). Unfortunately, I can't clearly remember the reason for this. I assume that your mentioning of shell scripts implies that this is running under a Linux guest. Back in the day, this patch was tailored very strictly against Windows guests, and that probably meant that doing so had a performance improvement over the way Windows handled pagetables and process distructions. Perhaps (I need some time to catch up) the PV-HVM thing has made this patch affect Linux as well, at the point that this has became a problem. Can you tell me in what guest OS this is experiencing a slow down? What is the order of magnitude of the performance decrease? I have no problem in reverting that part of the change, if it makes you happy. Thanks, Gianluca -- It was a type of people I did not know, I found them very strange and they did not inspire confidence at all. Later I learned that I had been introduced to electronic engineers. E. W. Dijkstra _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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