Re: [PATCH 1/2] tools, perf: Add a precise event qualifier v2

From: Vince Weaver
Date: Wed Jul 24 2013 - 14:46:11 EST

On Wed, 24 Jul 2013, Andi Kleen wrote:

> On Tue, Jul 23, 2013 at 05:27:43PM -0400, Vince Weaver wrote:
> >

> So format/precise would be
> flags:15-16
> on little endian. Looks good?

I'd prefer if it were


as the code you use to set the value looks like
I don't think you can even set bits 15-16 of flags directly, can you?

Althought having to have a parser being able to parse the names of all 50+
perf_event->attr arguments, then parse hex/decimal strings from another
file in sysfs, then trying to map that to binary fields in a complicated
structure that is then passed to a syscall gets a bit stupid at some
point; this is one of the silliest interfaces I've had to deal with and
I've done low-level X11 programming before.

Ideally we could do something sane, such as maybe having the event
descriptions in a library in userspace where it belongs but it's a bit
late to close the barn door now.

> > I'm a bit grumpy about this because I just finished fixing the fallout
> > from your last time breaking the ABI a few weeks ago when your broken code
> > started dumping non-hex fields into the sysfs event strings. I've learned
> Not sure what you're talking about?

I'm pretty sure it was one of your patches that added the new memory stuff
which had "ldlat=1" in one of the events, and that was not a hex value
prefixed by 0x as specified in the ABI documentation and thus broke
various parsers.

By the time I caught this the perf_event maintainers declared it was too
late to do anything about it.

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