From: Jens Axboe <axboe@fb.com>
Date: Wed, 3 Aug 2016 15:11:56 +0000 (-0600)
Subject: iolog: prevent early entry from skewing entire logging run
X-Git-Tag: fio-2.14~62
X-Git-Url: https://git.kernel.dk/?p=fio.git;a=commitdiff_plain;h=f5a568cfb7c2738f80399dc155c964bc26cbb4b3

iolog: prevent early entry from skewing entire logging run

If we go out of ramp time, our wakeup trigger could cause us to enter
too early in add_log_sample(). If that happens, the time diff could be
negative (so huge unsigned). Since we carry that forward, we end up
logging every entry and not just over the average window.

Signed-off-by: Jens Axboe <axboe@fb.com>
---

diff --git a/stat.c b/stat.c
index 7a35117a..d6787b7f 100644
--- a/stat.c
+++ b/stat.c
@@ -2139,7 +2139,9 @@ static long add_log_sample(struct thread_data *td, struct io_log *iolog,
 	 * need to do.
 	 */
 	this_window = elapsed - iolog->avg_last;
-	if (this_window < iolog->avg_msec) {
+	if (elapsed < iolog->avg_last)
+		return iolog->avg_last - elapsed;
+	else if (this_window < iolog->avg_msec) {
 		int diff = iolog->avg_msec - this_window;
 
 		if (inline_log(iolog) || diff > LOG_MSEC_SLACK)