Messages in this thread Patch in this message |  | | Date | Wed, 6 Feb 2013 20:42:18 +0100 | From | Oleg Nesterov <> | Subject | [PATCH 0/1] (Was uprobes/perf: pre-filtering) |
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On 02/06, Oleg Nesterov wrote: > > Btw, during the testing I noticed a minor problem (or problems) in tools/perf/, > I'll try to investigate...
To avoid the confusion, this has nothing to do with perf/uprobe/prefiltering changes.
Well. I am very new to this code, and I didn't even use perf before, it is quite possible I missed something/everything.
But I simply can't understand the logic behind perf_evlist__create_maps/etc.
OK, builtin-record.c:record sets .target->uses_mmap == T, this is correct, we are going to use perf_mmap().
But why do we need it? It is for perf_evlist__create_maps() to ensure we do not use cpu_map__dummy_new().
But. Even if we use perf_mmap(), "event->cpu == -1 && !event->attr.inherit" is fine. And indeed, "perf record -e whatever -p1" creates a single counter with "cpu = -1" and this works. Because, damn, perf_evlist__config_attrs() notices "evlist->cpus->map[0] < 0" and sets "opts->no_inherit = true".
But at the same time, this does not allow to do, say, "perf record -e whatever -C0 -p1". -C0 is simply ignored because when perf_evlist__create_maps() is called perf_target__has_task() == T due to "-p1".
Not to mention, there is no way to trace init and the children it will fork...
And otoh. "perf record -e whatever -i true" creates a counter for each cpu due to ->uses_mmap. This is suboptimal, but of course the hack like
--- a/tools/perf/builtin-record.c +++ b/tools/perf/builtin-record.c @@ -1081,6 +1078,8 @@ int cmd_record(int argc, const char **argv, const char *prefix __maybe_unused) if (!argc && perf_target__none(&rec->opts.target)) usage_with_options(record_usage, record_options); + rec->opts.target.uses_mmap = !rec->opts.no_inherit; + if (rec->force && rec->append_file) { ui__error("Can't overwrite and append at the same time." " You need to choose between -f and -A");
should not be even discussed.
And why opts->target.system_wide is only set by OPT_BOOLEAN("all-cpus") ? I meant, why I can't do "perf record -e whatever -C0" to create a "global" counter on CPU_0? This doesn't work because __cmd_record() sees !.system_wide and assumes we need perf_event__synthesize_thread_map() which silently fail.
So I am sending a single patch to fix the problem which complicated my testing. It is trivial but I am not sure it correct, please review.
Oleg.
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