Re: [Xen-devel] Measure performance of hypercalls

["George Dunlap" <George.Dunlap@xxxxxxxxxxxxx>]

On Wed, Oct 15, 2008 at 3:00 PM, Dan Magenheimer
<dan.magenheimer@xxxxxxxxxx> wrote:
> Hmmm... lots of interesting things can happen between a hypercall
> entry and exit, eg. domain switch, interrupts, timer queues, etc.
> So just taking a pair of timestamps is not likely to have the
> desired result.

Domain switch you can factor in, if you trace runstate changes as well
(albeit a bit tricky).  Long-term averages are probably what you
really want (since a one-off isn't going to affect performance too
much).  So if you filter out hypercalls interrupted by a context
switch, and do an average over the rest, the interrupts, timer queues,
&c should more or less disappear in the noise (unless they're a
significant source of overhead, in which case they need some attention
anyway).

I have a tool that will do a bunch of this stuff for vmexit/enter
analysis.  If there were hypercall enter/exit timestamp traces, it
could be modified to do the same for hypercalls.  Then we might think
about fun things like analyzing hypercall continuations and what not.
:-)

 -George

>
> I too am interested in a similar measurement (for a specific hypercall),
> so if there IS a way to do this with reasonable accuracy, please
> correct me.
>
>> On Wed, Oct 15, 2008 at 3:12 AM, Tommy Huang
>> <nbp0204@xxxxxxxxx> wrote:
>> > Hi all,
>> >
>> > I am wondering how to measure the performance of hypercalls.
>> > For example, how many X86 instructions are executed in Xen
>> when you issue a
>> > hypercall.
>> > Also, how to get the frequency of hypercalls which is that how many
>> > hypercalls have been issued during a period of time?
>> > Thanks in advance.
>> >
>> > - Nb
>> >
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>> >
>> >
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