On Wed, Nov 19 2008, Erwan Velu wrote: > Here come a typical output I have using fio. I added some line numbers > as an helper. > > 01: /dev/mydisk: (groupid=1, jobs=1): err= 0: pid=7433 > 02: write: io=79,112MiB, bw=72,774KiB/s, iops=740, runt=1139888msec > 03: slat (usec): min=9, max=572, avg=21.22, stdev= 7.03 > 04: clat (msec): min=2, max=668, avg=86.43, stdev=24.47 > 05: bw (KiB/s) : min= 0, max=80749, per=100.06%, avg=72815.92, > stdev=2318.78 > 06: cpu : usr=0.93%, sys=1.35%, ctx=722885, majf=0, minf=10031 > 07: IO depths : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=0.1%, > >=64=100.0% > 08: submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, > >=64=0.0% > 09: complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.1%, > >=64=0.0% > 10: issued r/w: total=0/843855, short=0/0 > 11: > 12: lat (msec): 4=0.01%, 10=0.03%, 20=0.38%, 50=6.53%, 100=64.24% > 13: lat (msec): 250=28.79%, 500=0.01%, 750=0.01% > > > I have some questions about the output. > > About Latencies: > Line 4, clat is reported to be at 86ms as average but line 12 is is > written that 100=64 250=29 > What's the meaning of "100=" ? Does it means "there were 64% of IOs > completed between 100 & 249 ms ?" > If yes, that's pretty surprising that while having 95% of my IOs that > are completed in more than 100ms, the average is reported as 86. > If "100=" means "IO between 50 and 99ms", thus output become pretty > confusing. The output could do with a bit of prettying up... It's explained in the documentation, though, The 100=64.24% field means that 64.24% of the ios completed within 50 and 99ms, as you indicate. > About IO depths: > In my config file I had set a depth to 64. Line 07 reports that 100% of > my IOs where >=64... cool but is it also said that 0.6% were spent on <=64K > Sounds to be a rounding effect but does this really means that some IOs > where sent with a short depth ? It's rounding, 0.1% indicates that it's over 0%. Since we build up the queue in the beginning, this is usually the case. > And then, how should I understan lines 8 & 9 that reports that 100% of > IOs were completed with a depth=4... What happened ? Same deal, 4 means 1-4 completions per io_getevents() call for your test case. So any attempt to retrieve completed IO from the system resulted in a return of 1-4 ios. > Hope this questions aren't too stupid ;o) Not at all, I'd appreciate constructive criticism on how to improve the output. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe fio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
