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SubjectRe: [PATCH 5/9] perf: Adding sysfs group format attribute for pmu device
On Fri, Jan 27, 2012 at 01:08:38PM -0800, Corey Ashford wrote:
> On 01/27/2012 06:34 AM, Jiri Olsa wrote:
> > Adding sysfs group 'format' attribute for pmu device that
> > contains a syntax description on how to construct raw events.
> >
> > The event configuration is described in following
> > struct pefr_event_attr attributes:
> >
> > config
> > config1
> > config2
> >
> > Each sysfs attribute within the format attribute group,
> > describes mapping of name and bitfield definition within
> > one of above attributes.
> >
> > eg:
> > "/sys/...<dev>/format/event" contains "config:0-7"
> > "/sys/...<dev>/format/umask" contains "config:8-15"
> > "/sys/...<dev>/format/usr" contains "config:16"
> >
> > the attribute value syntax is:
> >
> > line: config ':' bits
> > config: 'config' | 'config1' | 'config2"
> > bits: bits ',' bit_term | bit_term
> > bit_term: VALUE '-' VALUE | VALUE
> >
> > Adding format_defined bool to the struct pmu to specify wether
> > pmu defines its own set of format attributes (within the
> > attr_groups member) or the default format attributes should be
> > used:
> > "/sys/...<dev>/format/config" contains "config:0-63"
> > "/sys/...<dev>/format/config1" contains "config1:0-63"
> > "/sys/...<dev>/format/config2" contains "config2:0-63"
>
>
> Hi Jiri,
>
> I've been out of the perf_events loop for some time, but I did finally
> notice your patch series thread.
>
> I think what you've done is very good and I'm excited to see progress in
> this area. However, it's not clear to me that it is as generalized as
> it needs to be for some PMU's. I say this because not all events on a
> given PMU will have the same needed fields.

ok, I wasn't aware of this

>
> As an example, the IBM PowerEN processor has roughly 20 different PMU's
> on it. Some of those PMU's are quite complex and divide their events up
> into subsets, each with different fields. For example, some events may
> have a PID matching field, and others may have an bus number matching
> field, or matching mode field, etc. The fields are different widths,
> and may overlap in the config/1/2 space.
>
> It seems that there are two approaches you could take:
>
> 1) Keep your format, but allow the fields to overlap in the bit space.
> For example:
>
> "/sys/...<dev>/format/event" contains "config:0-7"
> "/sys/...<dev>/format/pidmatch" contains "config:8-15"
> "/sys/...<dev>/format/busmatch" contains "config:8-13"
>
> Note that busmatch overlaps pidmatch

currently format fields definitions may overlap, there's no check
to prevent that

>
> 2) Create event groups that have their overlapping config space
> separated out:
>
> "/sys/...<dev>/format/event" contains "config:0-7"
>
> "/sys/...<dev>.1/format/pidmatch" contains "config:8-15"
>
> "/sys/...<dev>.2/format/busmatch" contains "config:8-13"
>
>
> Notice the .1 and .2 on the <dev>.
>
> This might help the user understand which fields go together. I'm not
> sold on the .1 syntax... you could do it as <dev>.<event-group-name>/ or
> <dev>/<event-group-name>/... or whatever seems to make the most sense
> and is relatively easy to implement and use.

Though I'm not sure we want allow separate devices inside single pmu,
I think we could have multiple format groups if necessary :)

some quick ideas:

1) having format group attribute under format like:
<dev>/format/group1/..
<dev>/format/group2/..
<dev>/format/group2/..
...

2) having format group name within the format attribute name like:
<dev>/format/group1-krava1
<dev>/format/group1-krava2
<dev>/format/group2-krava3
...

3) having group name inside the foramt attributes like:
cat <dev>/format/group1-krava1
group1 config:0-1,62-63


I think I like the most ad 1)..

We could have something like default format directory if there's
only a single format group, like:
<dev>/format/default/krava1
<dev>/format/default/krava2
...

The perf event syntax could have something like '::' to classify
format attribute with a group like (none would go to default dir):

cpu/group1::config=1,group2::config1=2,config2=3/u
or
cpu::group1/config=1,config1=2,config2=3/u


Or we could say the format field names could not overlap and then
we dont need to specify group at all :) It'd be just for user's
awareness..

Any idea if we at all want to go this way? ;)

thanks,
jirka


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