On Fri, 13 Sep 2013, Peter Zijlstra wrote:
> On Fri, Sep 13, 2013 at 11:50:57AM +0200, Ingo Molnar wrote:
> > For example if we added 'type' as well we could expose the generic,
> > hardware-independent events via sysfs as well.
>
> Type is already fully implied by where you'll find the event in sysfs:
>
> /sys/bus/event_sources/devices/$PMU/events/
>
> needs
>
> perf_event_attr::type := /sys/bus/event_sources/devices/$PMU/type
OK, fine, another question then.
Is there any reason these values have to be human-readable?
The only reason you are using this crazy format I can see is because it
makes maintaining your personal userspace implementation (perf) easier at
the expense of everyone else who want to use this interface.
Honestly, an interface like
cat /sys/bus/event_sources/devices/$PMU/events/new_event
size=320,0xdeadbeef,0xcafef00d,....,0x000000
when you just set up an array, copy in the values, then memcpy() it into
place on top of a struct attr is a million times easier than what you are
propsing:
1. A huge complicated LEX/YACC parser
2. The parser has to read in many different files under ../format/..
and build up a tree of names and shift/masks
3. The event is read in and then text has to be parsed, values read,
and then shifting-masking to get a value for each register
4. A mapping has to be in the code of the various (of the over 40+)
fields in the struct perf_attr field, and each value has to
be put at the proper offset
5. If ever a new field is added to struct perf_attr, then any event
using it breaks until your parser is updated with all the info
about this field.
It's huge, takes up non-swappable kernel mem with lots of individual sysfs
files, requires a complex parser for what should be just a simple
config setup, and is fragile when new fields are added.
But of course since perf is tightly coupled into the kernel source tree
you can get away with it. I guess I should just be glad you aren't
exporting it as XML or something.
Vince
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