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Re: [Qemu-devel] [RFC] tracing: consistent usage of "disable" in "trace-
From: |
Daniel P. Berrange |
Subject: |
Re: [Qemu-devel] [RFC] tracing: consistent usage of "disable" in "trace-events" |
Date: |
Mon, 8 Nov 2010 15:25:56 +0000 |
User-agent: |
Mutt/1.4.1i |
On Mon, Nov 08, 2010 at 03:42:15PM +0100, Lluís wrote:
> On the current implementation, the "disable" keyword in "trace-events"
> has different semantics, depending on the backend:
>
> * nop : ignored (not a problem)
> * simple : enables tracing, but sets dynamic state to disable
> * ust : disables tracing (uses nop backend)
> * dtrace : same as simple
>
> Would it be possible to just use nop whenever the event is disabled in
> trace-events? If you agree I can cook the patch, as it's pretty simple.
I don't particularly see the point of the 'disable' keyword existing at
all, unless there are performance implications for a particular trace
backend. For the DTrace backend I strip & ignore the disable keyword
because probes that are compiled in, reduce to a inline conditional
check that has no serious overhead when no trace client is active.
Regards,
Daniel
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