Re: [Xen-devel] [Patch] support of lock profiling in Xen

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 08/10/2009 09:38, "Juergen Gross" <juergen.gross@xxxxxxxxxxxxxx> wrote:

>> There's also the question of whether this really gets you useful extra info
>> than can be digested from a xentrace run. I suppose at least the info is
>> easier to understand, and not many people know how to drive xentrace.
> 
> It helped me a lot for narrowing down my performance problem with a 8 vcpu
> BS2000 system (this was the main reason I made the patch).
> Finding such a problem in xentrace is quite a bit of work. xentrace produced
> over 500 MB of data in 30 seconds, while reading the xenlockprof output
> revealed the bottleneck in seconds.
> 
> And I think the lock profiling tool is much better for evaluating
> optimizations in Xen regarding lock conflicts, if the differences are only
> a few percent.

Okay, well the only thing I'm dead against in a lockmeter patch is requring
dynamic registration and unregistration of individual locks. Largely because
I see a never-ending stream of fix this unregistration, fix that
unregistration, stretching out before me, because callers will forever be
getting broken.

I suppose most locks are either global or per-domain, so perhaps you could
just have domain create/destroy hooks into lockmeter, to alloc/free an array
of per-domain locks? Would that actually be an argument for a perfc-style
central declaration of all profileable locks, so you could indicate which
are global and which are per-domain?

 -- Keir



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