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Re: [Qemu-devel] [PATCH 1/3] qsp: QEMU's Synchronization Profiler

From: Emilio G. Cota
Subject: Re: [Qemu-devel] [PATCH 1/3] qsp: QEMU's Synchronization Profiler
Date: Wed, 15 Aug 2018 19:55:14 -0400
User-agent: Mutt/1.9.4 (2018-02-28)

On Wed, Aug 15, 2018 at 00:53:23 -0400, Emilio G. Cota wrote:
> On Wed, Aug 15, 2018 at 11:09:42 +0800, Fam Zheng wrote:
> > On Mon, 08/13 13:11, Emilio G. Cota wrote:
> > > +  --enable-sync-profiler) sync_profiler="yes"
> > > +  ;;
> > 
> > Curious, not asking for a change: can this be made a runtime option instead 
> > of
> > compile time, since there's no library dependencies? That should make this
> > somewhat easier to use.
> Good point. I'll do some profiling tomorrow to see how the latency
> of the locking primitives could be minimized (ideally, not using
> the profiler should just add a well-predicted branch).

I reduced it to just a branch, but still, I measured a few percentage
points (1-2%, depending on the machine) slowdown when this is a
run-time option. (This is for a bootup+shutdown test of a guest.)

So I'll keep it as a build-time option, then.



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