I forgot to mention that the "--filename=random_readwrite_test.fio" is being written to the ISCSI filesystem, so thank you for bringing that up. >From your response, I should not sum the avg read latency and the avg write latency. Instead, I should average the average or take the higher of the two two numbers as the total latency of my fio test. Correct? Thank you in advance. -----Original Message----- From: fio-owner@xxxxxxxxxxxxxxx [mailto:fio-owner@xxxxxxxxxxxxxxx] On Behalf Of Sitsofe Wheeler Sent: Monday, August 19, 2019 1:03 AM To: Eliezer Nebab Cc: fio Subject: Re: Total latency (lat) of a workload test Hi, On Mon, 19 Aug 2019 at 00:02, Eliezer Nebab <eliezer@integritech.solutions> wrote: > > Hello, > > I have the following workload: > > fio --randrepeat=1 --ioengine=libaio --direct=1 --sync=1 --name=test --filename=random_readwrite_test.fio --overwrite=1 --iodepth=64 --size=5GB --readwrite=randrw --rwmixread=50 --rwmixwrite=50 --bs=32k --runtime=60 --time_based --ramp_time=15 > > With the following result: > > read : io=1949.4MB, bw=33249KB/s, iops=1038 , runt= 60035msec > slat (usec): min=4 , max=30100 , avg=23.92, stdev=240.73 > clat (msec): min=1 , max=80 , avg=31.59, stdev= 8.94 > lat (msec): min=1 , max=80 , avg=31.61, stdev= 8.94 > > write: io=1830.3MB, bw=31219KB/s, iops=975 , runt= 60035msec > slat (usec): min=5 , max=30150 , avg=35.61, stdev=293.88 > clat (msec): min=1 , max=80 , avg=31.91, stdev= 8.82 > lat (msec): min=1 , max=80 , avg=31.95, stdev= 8.81 > > This is a 2000 iops iscsi. The read operation shows a 31.61 (msec) lat and the write operation at 31.95 (msec). What is the correct way to interpret the total latency of this fio workload? Do you add the read lat (31.61) plus write lat (31.95) to get the overall latency for this workload? I'm afraid I don't understand the question. I guess you're saying "can I flatten the read and write latencies into one number by summation" and my feeling would be no you can't because then it's not per I/O data that you are talking about - you have two I/Os worth of latency (I'm not statician though). I'd probably make some statement like "the average per I/O latency with workload XYZ was approximately 32 milliseconds regardless of direction" (if you're about to publish results don't forget about https://github.com/axboe/fio/blob/master/MORAL-LICENSE ). Possibly averaging the average is slightly more meaningful or taking the higher of the two two numbers. Just be aware it looks like the workload you're doing has a filesystem between you and your disk and by default fio is going to be making that "random_readwrite_test.fio" file in the current working directory. If that's not a filesystem on the iSCSI disk you actually wanted to test or it is a filesystem that ignores the direct flag (https://stackoverflow.com/a/46377629/ ) then results may not be as you expect etc. I'd recommend at least checking what you get doing I/O against the block device directly but be aware that doing so will DESTROY any data (e.g. like a filesystem) already there! -- Sitsofe | http://sucs.org/~sits/
