linux-kernel - Re: [PATCH perf 0/2] perf: trace-event-parse: support more operators and print formats

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Date:	Thu, 7 Apr 2011 13:25:04 -0700
From:	David Sharp <dhsharp@...gle.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	linux-kernel@...r.kernel.org, mrubin@...gle.com,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...e.hu>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH perf 0/2] perf: trace-event-parse: support more operators
 and print formats

On Thu, Apr 7, 2011 at 7:26 AM, Frederic Weisbecker <fweisbec@...il.com> wrote:
> On Wed, Apr 06, 2011 at 07:01:40PM -0700, David Sharp wrote:
>> Hi, any feedback on these patches? I think it's important that perf
>> and trace-cmd don't drift in the syntax they accept.
>>
>> d#
>
> Sorry, I forgot these.
>
>> On Mon, Mar 21, 2011 at 3:34 PM, David Sharp <dhsharp@...gle.com> wrote:
>> > These patches correspond to similar patches recently applied to trace-cmd
>> >
>> > [ Re-sending with more Cc's ]
>> >
>> > Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
>> > Cc: Frederic Weisbecker <fweisbec@...il.com>
>> > Cc: Steven Rostedt <rostedt@...dmis.org>
>> > Cc: Ingo Molnar <mingo@...e.hu>
>> > Cc: Stephane Eranian <eranian@...gle.com>
>> >
>> >
>> > David Sharp (2):
>> >  perf: trace-event-parse: support additional operators: '!', '~',  and
>> >    '!='
>> >  perf: trace-event-parse: support printing short fields
>
> So we now have trace events that use these new operations? Which ones?
> A quick grep on "TP_printk" and "!" doesn't give me any result, probably
> because TP_printk is often multiline.
>

We (google) have some events that use '~' and '!', and I threw in '!='
mostly because it needed to be differentiated from '!' during
tokenizing.

We set the MSB of the syscall number in raw_syscalls events to
indicate a compat syscall, and use '~' and '!' (and '&' and '>>') to
extract the bit. eg, for sys_exit:
print fmt: "NR %ld = %ld isCompat: %d", REC->id & (~0UL>>1), REC->ret,
!!(REC->id & ~(~0UL>>1))
Patches for this will be forthcoming, but, you know: time.

If our internally-added events are not sufficient reason, I think it
still makes sense to support as much of the C expression syntax as
reasonable. Leaving holes in the syntax mostly just causes frustration
when these operators would be useful. And since they do work with the
in-kernel output (which has the whole compiler to leverage), use of
unsupported operators can go unnoticed for quite a while.

Thanks,
d#
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