linux-kernel - Re: [PATCH] tracing/markers: make markers select tracepoints

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Message-ID: <49A276E0.9010603@redhat.com>
Date:	Mon, 23 Feb 2009 12:13:52 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Frederic Weisbecker <fweisbec@...il.com>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org
Subject: Re: [PATCH] tracing/markers: make markers select tracepoints

Ingo Molnar wrote:
>         KVMTRACE_3D(MSR_READ, &svm->vcpu, ecx, (u32)data,
>                     (u32)(data >> 32), handler);
>
> after:
>
> 	kvm_trace("MSR_READ: %p, %08lx, %016Lx\n", &svm->vcpu, ecx, data);
>
> As a result all these traces would become a lot more readable 
> (and a lot more flexible) both in the source code, and in the 
> trace output stage.
>
> And any ad-hoc tracepoint can be added, without worrying about 
> the name of the macro or the number of type of arguments. Note 
> that in this specific example we didnt need to split up the u64 
> 'data' into two 32-bit values, nor do we have to pass in the 
> 'handler' name, nor do we have to provide a MSR_READ 
> enumeration.
>
> The tracing-disabled case would still be as fast - a single 
> branch check.
>
> Avi, what do you think, any objections against an RFC patchset 
> that shows this off?
>
>   

Definitely, as long as formatting is performed after the data is 
gathered (say, in userspace).  kvmtrace can generate around 1M 
events/sec/cpu, so we need truly low overhead.

-- 
error compiling committee.c: too many arguments to function

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