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authorVasily Tarasov <tarasov@vasily.name>2014-11-09 20:22:24 -0700
committerJens Axboe <axboe@fb.com>2014-11-09 20:24:14 -0700
commite5437a073e658e8154b9e87bab5c7b3b06ed4255 (patch)
treec8eb238cfc1a5a9e4c2b2e199b79c732563d851b /stat.h
parent988d97bac90c9ff3ee40a8ccd588fdf78f19320d (diff)
downloadfio-e5437a073e658e8154b9e87bab5c7b3b06ed4255.tar.gz
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Fix for a race when fio prints I/O statistics periodically
Below is the demonstration for the latest code in git: Job-file: [job] filename=/dev/sda rw=randread blocksize=4096 direct=1 time_based=1 runtime=300 numjobs=16 Command line: fio --output-format=json --status-interval=10 /tmp/job.file | tee /tmp/fio.out After parsing json and printing per-job "read->runtime" and "read->iops" in two columns, one can see this: runtime iops 9854 4762 19861 4724 29867 4711 39873 4705 49880 4701 59886 4698 69894 4696 79900 4694 89907 4693 99913 4692 109919 4692 119926 4691 129933 4691 139940 4691 149946 4691 159953 4690 169959 4690 179966 4690 189972 4690 199978 4690 209984 4690 219990 4690 229996 4690 240002 4690 250009 4690 260015 4690 270021 4690 280027 4690 290033 4690 600043 2344 <--- You can see a spurious jump in runtime here 300001 4690 The problem is two-fold, IMHO: 1) td->ts.runtime[DDIR_READ/DDIR_WRITE/DDIR_TRIM] are set in microseconds instead of milliseconds in thread_main() function. The values are later converted to milliseconds (after exiting from the loop in thread_main()), but it is too late for the out-of-band access by the helper_thread (the one that prints periodic statistics). 2) The helper_thread in __show_running_run_stats() temporarily adds to td->ts.runtime[DDIR_READ/DDIR_WRITE/DDIR_TRIM] the time that has passed since the beginning of the loop (td->start). However, the same addition happens in thread_main() by the job thread and td->start is not reset atomically with this addition. As a result, the runtime can be added twice. (That's why in the output we see 600043, which is approximately twice larger than the previous reading). My proposal is to make the job threads updating both td->ts.runtime and td->start atomically by using an already existing stat_mutex. __show_running_run_stats() already takes this mutex where needed. Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'stat.h')
-rw-r--r--stat.h2
1 files changed, 2 insertions, 0 deletions
diff --git a/stat.h b/stat.h
index 8aefe03c..8b4416cf 100644
--- a/stat.h
+++ b/stat.h
@@ -214,6 +214,8 @@ struct jobs_eta {
uint8_t run_str[];
} __attribute__((packed));
+extern struct fio_mutex *stat_mutex;
+
extern struct jobs_eta *get_jobs_eta(int force, size_t *size);
extern void stat_init(void);