On Mon, Feb 01, 2010 at 02:17:35AM -0600, Tom Zanussi wrote: > Here's one way, using the tracepoint filters - it does make a big > difference in this case. > > Before (using the new -P option, which includes perf in the trace > data): > > root@tropicana:~# perf record -c 1 -f -a -M -R -e filemap:add_to_page_cache -e filemap:find_get_page -e filemap:remove_from_page_cache -P sleep 5 > [ perf record: Woken up 0 times to write data ] > [ perf record: Captured and wrote 71.201 MB perf.data (~3110815 samples) ] > > After (filters out events generated by perf): > > root@tropicana:~# perf record -c 1 -f -a -M -R -e filemap:add_to_page_cache -e filemap:find_get_page -e filemap:remove_from_page_cache sleep 5 > [ perf record: Woken up 1 times to write data ] > [ perf record: Captured and wrote 0.309 MB perf.data (~13479 samples) ] > > Tom > > [PATCH] perf record: filter out perf process tracepoint events > > The perf process itself can generate a lot of trace data, which most > of the time isn't of any interest. This patch adds a predicate to the > kernel tracepoint filter of each recorded event type which effectively > screens out any event generated by perf. > > Assuming the common case would be to ignore perf, this makes it the > default; the old behavior can be selected by using 'perf record -P'. I think filtering out perf from the instrumentation is a very desirable features. But I see two drawbacks with this patch. First of all, we want to keep perf as a part of the instrumentation as a default behaviour I think, as it is a true part of the system wide load. So I would rather suggest to keep it as a default and have an exclude_perf option instead of include_perf. The other downside is that this filtering only applies to ftrace events and not to other perf events. I would expect an exclude_perf option to apply to every events, not just a family of them. This is not that easy though. It's trivial for a process bound instrumentation as we only need to use enable_on_exec for that (assuming we create the targeted process from perf). Otherwise we need the cpu events to filter out a given context, which needs to be done from the kernel, on events scheduling time. It's just an idea, I'm adding more interested parties in Cc. Thanks. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>