Messages in this thread | | | Subject | Re: [PATCH] perf parse events: Fix invalid precise_ip handling | From | zhangmengting <> | Date | Wed, 15 Nov 2017 09:00:03 +0800 |
| |
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. > 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.
Thanks Mengting Zhang
> thanks, > jirka > -- > To unsubscribe from this list: send the line "unsubscribe linux-perf-users" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > > . >
| |