Messages in this thread Patch in this message |  | | | Date | Fri, 14 Sep 2012 10:05:03 -0600 | | From | David Ahern <> | | Subject | Re: perf script: rwtop: SIGALRM and pipe read race |
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On 9/14/12 9:39 AM, Andrew Jones wrote: > > I recently tried 'perf script rwtop', and it immediately failed with > 'failed to read event header'. Running it through strace I found that the > when rwtop.pl is reading from the pipe, and gets one of it's alarms, that > the ERESTARTSYS seems to confuse it - causing it to fail. It also appears > that the problem only happens early in execution, or not at all. If I get > lucky and don't hit the problem right away, then rwtop will run fine as > long as I want, without any ERESTARTSYS's in its trace. I also found that > I can avoid hitting the problem by throwing a 'pv -q' in front of the perf > command in tools/perf/scripts/perl/bin/rwtop-report. Which I guess slows > things down in the reader enough to always avoid the race. > > Sorry I don't have a solution (patch). I'll look at it more as time > permits, but I thought I'd get it reported for starters though.
This fixes the run-time problem:
diff --git a/tools/perf/util/util.c b/tools/perf/util/util.c index 1b8775c..a4371ae 100644 --- a/tools/perf/util/util.c +++ b/tools/perf/util/util.c @@ -142,6 +142,9 @@ int readn(int fd, void *buf, size_t n) while (n) { int ret = read(fd, buf, n);
+ if ((ret < 0) && (errno == EINTR)) + continue; + if (ret <= 0) return ret;
The only problem you will find with rwtop is that bytes_read will be really whacky. I traced it to:
if ($ret > 0) { printf("comm %s bytes_read %d\n", $common_comm, $ret); $reads{$common_pid}{bytes_read} += $ret; Somehow the $ret > 0 is passing when in fact it is negative. I do not know much about perl to fix it. David
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