From mboxrd@z Thu Jan  1 00:00:00 1970
From: aburov@orc-group.com (Andrei Burov)
Date: Tue, 2 Jun 2015 17:32:44 +0300
Subject: [lttng-dev] Unable to use stalled-cycles-frontend perf counter
Message-ID: <556DBE8C.7030306@orc-group.com>

Hello!

I've encountered a problem with lttng (LTTng Trace Control) 2.5.0 -
Fumisterie. When I am trying to access stalled-cycles-frontend perf
counter, it somehow corrupts the tracefile. Below is a simple test which
is using code of hello program from lttng doc.

$ls
hello  hello.c  hello-tp.c  hello-tp.h  hello-tp.o  hello-tp.tp
$lttng create
Session auto-20150602-160131 created.
Traces will be written in /home/user/lttng-traces/auto-20150602-160131
$lttng enable-event -u hello_world:my_first_tracepoint
UST event hello_world:my_first_tracepoint created in channel channel0
$lttng add-context -u -t perf:thread:stalled-cycles-frontend
UST context perf:thread:stalled-cycles-frontend added to all channels
$lttng start
Tracing started for session auto-20150602-160131
$./hello
Hello, World!
Press Enter to continue...

Quitting now!
lttng stop
Waiting for data availability.
Tracing stopped for session auto-20150602-160131
$lttng view
Trace directory: /home/user/lttng-traces/auto-20150602-160131
[error] Cannot open any trace for reading.
[error] opening trace "/home/user/lttng-traces/auto-20150602-160131" for
reading.
[error] none of the specified trace paths could be opened.
$lttng destroy && lttng create
Session auto-20150602-160131 destroyed
Session auto-20150602-160224 created.
Traces will be written in /home/user/lttng-traces/auto-20150602-160224
$lttng enable-event -u hello_world:my_first_tracepoint
UST event hello_world:my_first_tracepoint created in channel channel0
$lttng add-context -u -t perf:thread:cycles
UST context perf:thread:cycles added to all channels
$lttng start
Tracing started for session auto-20150602-160224
$./hello
Hello, World!
Press Enter to continue...

Quitting now!
$lttng stop
Waiting for data availability.
Tracing stopped for session auto-20150602-160224
$lttng view
Trace directory: /home/user/lttng-traces/auto-20150602-160224

[16:03:14.431724221] (+?.?????????) krypton.com
hello_world:my_first_tracepoint: { cpu_id = 1 }, { perf_thread_cycles =
281474976715686 }, { my_string_field = "hi there!", my_integer_field = 23 }
[16:03:14.432296656] (+0.000572435) krypton.com
hello_world:my_first_tracepoint: { cpu_id = 1 }, { perf_thread_cycles =
281474976722947 }, { my_string_field = "./hello", my_integer_field = 0 }
[16:03:14.432300284] (+0.000003628) krypton.com
hello_world:my_first_tracepoint: { cpu_id = 1 }, { perf_thread_cycles =
281474976726469 }, { my_string_field = "x^2", my_integer_field = 1 }

Thanks for your help!
Andrei

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