Re: problem with the "write_bw_log" parameter in a virtualized environment using a write iopattern

[Jens Axboe <jens.axboe@oracle.com>]

On Fri, Jul 31 2009, Ivan Frain wrote:
> Hi everybody,
>
> I'am using fio in a vmware virtualized environment. I have got a guest
> virtual machine based on centos5.2 on which I run fio in order to
> measure the virtual disks IO performances.
> I use the "write_bw_log" parameter in order to build graphs for the
> experiments but the problem is that the file generated by fio for each
> job is empty (size = 0).
> However, i also use "write_clat_log" parameter and the 'clat.log' and
> 'slat.log' files are not empty. The mean bandwidth in the fio output
> summary seams to be good.

I wonder how long that bug has been there... It's due to a botched
memcpy in the fio core. There are two stat sample times, yet it
overwrites only the first one (being 0, or DDIR_READ, which explains why
the read one works).

Try the below patch, it's also committed now.

diff --git a/fio.c b/fio.c
index ba9e384..7ad1b57 100644
--- a/fio.c
+++ b/fio.c
@@ -1105,7 +1105,10 @@ static void *thread_main(void *data)
 	clear_state = 0;
 	while (keep_running(td)) {
 		fio_gettime(&td->start, NULL);
-		memcpy(&td->ts.stat_sample_time, &td->start, sizeof(td->start));
+		memcpy(&td->ts.stat_sample_time[0], &td->start,
+				sizeof(td->start));
+		memcpy(&td->ts.stat_sample_time[1], &td->start,
+				sizeof(td->start));
 		memcpy(&td->tv_cache, &td->start, sizeof(td->start));
 
 		if (td->o.ratemin[0] || td->o.ratemin[1])

-- 
Jens Axboe