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So, what value should we read to get the in out operations per second per process?

I've tried /proc/[pid]/io which returns these values:

root@node:~# cat /proc/31597/io
rchar: 213260190
wchar: 462308212
syscr: 23275044
syscw: 47797624
read_bytes: 894867968
write_bytes: 27645691392
cancelled_write_bytes: 0

From definition:

syscr, syscw - Counters for number of I/O operation (respectively: read and write). We may use then to compute average amount of data passed in one system call.

So, I think last value of syscw minus the previous value of syscw after a second should give me the write operation count that has been performed by process 31597

However, when the process is doing around 5MB/sec writes (small files), I get the value as 6500 IOPS for writing and that doesn't look correct to me.

Any ideas?

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Thats the number of read/write syscalls, these dont translate to IOPs, especially when the reads come from page cache and writes go to dirty writeback. – Matthew Ife Apr 4 '14 at 18:11
    
Any possibility to get the actual IOPS? – ispirto Apr 4 '14 at 18:21
    
Not unless you write with direct IO (O_DIRECT), then you can divide wchar by the device sector size. Otherwise it makes little sense to measure IOPS per-process, because all the writes get bundled into writeback or fetched from pagecache. If you only care about what really lands on disk you can use iotop or pidstat -d to obtain pid statistics. – Matthew Ife Apr 4 '14 at 18:27
up vote 2 down vote

iotop can be the program you are looking for. It is like top, but for I/O.

You need a 2.6.20 or better kernel and root privileges.

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4  
I'm not looking for the byte count. I'm looking for the operation count. – ispirto Apr 4 '14 at 18:32

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