On Fri, 2009-08-21 at 16:47 +0200, stephane eranian wrote:
> Hi,
>
> Well, I tried that and it brings more complexity than needed
> especially with regards to
> extracting the ID for events when you're doing grouping.
>
> To extract the ID, one has to read out a struct as follows:
> * { u64 nr;
> * { u64 time_enabled; } && PERF_FORMAT_ENABLED
> * { u64 time_running; } && PERF_FORMAT_RUNNING
> * { u64 value;
> * { u64 id; } && PERF_FORMAT_ID
> * } cntr[nr];
> * } && PERF_FORMAT_GROUP
>
> Supposedly, you should have to do this only once per group. Reading
> this stuff using the group leader should yield the values of all the other
> events. This is not what I have observed. All events report the same
> ID as the leader. Not clear why.
Hmm, that's a bug alright.
> As I suggested in a previous message, I don't think all of this is necessary.
> If a tool was able to pass the ID to associate with an event, then there
> would be no need for a read(). Furthermore, it would make it easier to pick
> an ID which suites the tool's data structure. For instance, if you create
> 4 events in a group, the ID could be 0,1,2,3 and would most likely map to
> an index in the array used by the tool to manage the perf_counter structures.
> That would also make it easier in the critical path in the signal handler. No
> need to have a lookup table to map "random" ID to ID more relevant
> for the tool. The ID does not need to be very wide. IDs are relevant only if
> one uses group sampling. Therefore the ID needs to identify an event within
> a group. Could use a reserved field in perf_counter_attr or add an ioctl() to
> assign an ID.
ID are also needed when you want to allow mixing of the output buffers
(in any sense). That is, perf writes all mmap() data into a single file,
which mixes the streams, the other example is the output redirection
patch I posted the other day which basically does the same in-kernel.
A user-provided ID is still possible by extending perf_counter_attr. We
could add this later.
We still need a per-counter unique ID for the inherited thing, and I was
worrying that perhaps we would need to worry about collisions, but I
think these id spaces can be considered separate.
---
Subject: perf_counter: Fix typo in read() output generation
When you iterate a list, using the iterator is useful.
Signed-off-by: Peter Zijlstra <a.p.zijls...@chello.nl>
---
kernel/perf_counter.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 36f65e2..f274e19 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -1791,7 +1791,7 @@ static int perf_counter_read_group(struct perf_counter
*counter,
size += err;
list_for_each_entry(sub, &leader->sibling_list, list_entry) {
- err = perf_counter_read_entry(counter, read_format,
+ err = perf_counter_read_entry(sub, read_format,
buf + size);
if (err < 0)
return err;
------------------------------------------------------------------------------
Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day
trial. Simplify your report design, integration and deployment - and focus on
what you do best, core application coding. Discover what's new with
Crystal Reports now. http://p.sf.net/sfu/bobj-july
_______________________________________________
perfmon2-devel mailing list
perfmon2-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/perfmon2-devel
