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
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