[PATCH RESEND] Fix sum_stat() bug in group_reporting.

[Zheng Liu <gnehzuil@xxxxxxxxx>]

From: Zheng Liu <wenqing.lz@xxxxxxxxxx>

Write samples in io_stat does not be counted with rw=randread, vice versa.
Then, in sum_stat() function, it will cause 0/0 in calculating mean and S,
and 'nan' is printed. So it should return immediately when src->samples is
equal to 0.

the error result is as follows:
  write: io=8328.0KB, bw=1582.7KB/s, iops=395 , runt=  5262msec
    clat (usec): min=58 , max=293353 , avg= -nan, stdev= -nan
     lat (usec): min=59 , max=293353 , avg= -nan, stdev= -nan
    bw (KB/s) : min=   92, max=  804, per=-nan%, avg= -nan, stdev= -nan

the configuration file used:

[global]
direct=1
ioengine=psync
bs=4k
filename=/dev/sdb1
runtime=5
group_reporting
loops=50

[read]
rw=randread
numjobs=8

[write]
rw=randwrite
numjobs=8

CC: Jens Axboe <jaxboe@xxxxxxxxxxxx>
CC: Yu-ju Hong <yjhong@xxxxxxxxxx>
Signed-off-by: Zheng Liu <wenqing.lz@xxxxxxxxxx>
---
 stat.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/stat.c b/stat.c
index d2cc775..3662fd9 100644
--- a/stat.c
+++ b/stat.c
@@ -618,6 +618,9 @@ static void sum_stat(struct io_stat *dst, struct io_stat *src, int nr)
 {
 	double mean, S;
 
+	if (src->samples == 0)
+		return;
+
 	dst->min_val = min(dst->min_val, src->min_val);
 	dst->max_val = max(dst->max_val, src->max_val);
 
-- 
1.7.1

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