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SubjectRe: [PATCH] perf record: mmap output file - RFC
On 9/26/13 11:51 AM, Jiri Olsa wrote:
> but it's still faster, since we finally get perf a chance to sleep ;-)
>
> new time:
> real 0m30.392s
> user 0m0.041s
> sys 0m0.389s
>
> old time:
> real 0m32.235s
> user 0m3.080s
> sys 0m14.444s
>

Another data point on the performance improvement of perf itself. Using
openssl speed as a workload and perf-stat to collect information about
the perf-record process only:

perf stat -i -- perf record -g -o /tmp/perf.data openssl speed aes

With write():
158.606380 task-clock
72 context-switches
34 cpu-migrations
5,400 page-faults
336,054,007 cycles
137,804,036 stalled-cycles-frontend
74,505,914 stalled-cycles-backend
474,401,639 instructions
91,246,072 branches
1,968,289 branch-misses

With mmap():
50.314270 task-clock
61 context-switches
7 cpu-migrations
3,958 page-faults
93,585,618 cycles
64,878,225 stalled-cycles-frontend
41,680,427 stalled-cycles-backend
81,552,219 instructions
15,301,389 branches
387,230 branch-misses

So time, CPU cycles, instructions all drop by more than a factor of 3.

David


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