Messages in this thread | | | Date | Mon, 20 Nov 2017 08:33:41 +0100 | From | Jiri Olsa <> | Subject | Re: [PATCH] perf parse events: Fix invalid precise_ip handling |
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On Wed, Nov 15, 2017 at 09:00:03AM +0800, zhangmengting wrote: > Hi Jiri, thanks for your detailed review, please see my comments inline. > > > On 2017/11/10 18:39, Jiri Olsa wrote: > > On Fri, Nov 10, 2017 at 04:28:37PM +0800, Mengting Zhang wrote: > > > > SNIP > > > > > diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c > > > index 39b1596..25225f4 100644 > > > --- a/tools/perf/util/parse-events.c > > > +++ b/tools/perf/util/parse-events.c > > > @@ -1369,6 +1369,32 @@ struct event_modifier { > > > int pinned; > > > }; > > > +static int perf_get_max_precise_ip(void) > > > +{ > > > + int max_precise_ip = 0; > > > + struct perf_event_attr attr = { > > > + .type = PERF_TYPE_HARDWARE, > > > + .config = PERF_COUNT_HW_CPU_CYCLES, > > > + }; > > > + > > > + event_attr_init(&attr); > > > + > > > + attr.precise_ip = 3; > > > + attr.sample_period = 1; > > > + > > > + while (attr.precise_ip != 0) { > > > + int fd = sys_perf_event_open(&attr, 0, -1, -1, 0); > > > + if (fd != -1){ > > > + close(fd); > > > + break; > > > + } > > > + --attr.precise_ip; > > > + } > > > + max_precise_ip = attr.precise_ip; > > > + > > > + return max_precise_ip; > > > +} > > we already have a function for that, please check perf_event_attr__set_max_precise_ip > Yeah, I've checked that function. But perf_event_attr__set_max_precise_ip() > will change attr.precise_ip > into the max precise ip available. > > In this case, perf should only check whether the user-specified precise_ip > is greater than the max > precise_ip without changing it into maximum. Here, introduce > perf_get_max_precise_ip() to return > the max precise ip and do not change attr.precise_ip. > > But you reminds me that perf_get_max_precise_ip() can be simplied.
well both do the same.. probe kernel for max precise level, so we can keep just one function for that
> > also I think the precise level is not generic for all the events, > > so you should check it for specific perf_event_attr later, when > > the attr is ready, not in modifier parsing > You are right, and I would check it for specific perf_event_attr. > > BTW, I have a question. If the user-specified precise_ip is greater than the > max precise_ip, I wonder > whether it is better to adjust the user-specified precise_ip to the maximum > available.
no, I think that user defined precise level should stay the way the user wants it.. we don't want more angry users ;-)
jirka
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