linux-kernel - Re: [PATCH 0/2] perf: Redesign trace events reordering

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Date:	Wed, 05 May 2010 00:48:47 -0500
From:	Tom Zanussi <tzanussi@...il.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Arnaldo Carvalho de Melo <acme@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Masami Hiramatsu <mhiramat@...hat.com>
Subject: Re: [PATCH 0/2] perf: Redesign trace events reordering

Hi Frederic,

On Wed, 2010-05-05 at 02:03 +0200, Frederic Weisbecker wrote:
> I recently noticed that the new reordering design is broken
> when it deals with tons of events.
> 
> This patchset provides another algorithm to deal with that,
> tested without any problem.
> 
> And since it involves more frequent flushes, I guess it could
> plug nicely with the live mode.

Very nice!  I tried these out with live mode and it seems to work fine,
after applying the patch below.

I initially had a problem with 'unexpected end of event stream' errors,
then noticed that the FINISHED_ROUND events were basically just headers
with no data, which caused the read of the 0-length payload to appear as
end-of-stream.

I'll do some more testing (and fix some warnings in the scripts that
this mode seems to elicit), but it seems so far to work pretty well for
live mode...

Tom

From: Tom Zanussi <tzanussi@...il.com>
Date: Wed, 5 May 2010 00:27:40 -0500
Subject: [PATCH] perf/live-mode: handle payload-less events

Some events, such as the PERF_RECORD_FINISHED_ROUND event consist of
only an event header and no data.  In this case, a 0-length payload
will be read, and the 0 return value will be wrongly interpreted as an
'unexpected end of event stream'.

This patch allows for proper handling of data-less events by skipping
0-length reads.

Signed-off-by: Tom Zanussi <tzanussi@...il.com>
---
 tools/perf/util/session.c |   19 +++++++++++--------
 1 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 9401909..00ab298 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -696,15 +696,18 @@ more:
 	p = &event;
 	p += sizeof(struct perf_event_header);
 
-	err = do_read(self->fd, p, size - sizeof(struct perf_event_header));
-	if (err <= 0) {
-		if (err == 0) {
-			pr_err("unexpected end of event stream\n");
-			goto done;
-		}
+	if (size - sizeof(struct perf_event_header)) {
+		err = do_read(self->fd, p,
+			      size - sizeof(struct perf_event_header));
+		if (err <= 0) {
+			if (err == 0) {
+				pr_err("unexpected end of event stream\n");
+				goto done;
+			}
 
-		pr_err("failed to read event data\n");
-		goto out_err;
+			pr_err("failed to read event data\n");
+			goto out_err;
+		}
 	}
 
 	if (size == 0 ||
-- 
1.6.4.GIT



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