Am Mittwoch, 9. Mai 2012 schrieb Martin Steigerwald: > Hi Jens, hi everyone, > > Well mails from my mail client seem to appear here. > > > I have some questions regarding fio latencies. > > There are three kind of latencies described in README, from which fio 2.0.7 > only displays clat and lat: > > slat = submission latency > > clat = completion latency > > lat = I/O completion latency > > > Now I try to understand the README but I am not sure whether I really got > the difference. > > I understand: > > slat: The time to submit the I/O. This is the time after which a syscall > returns to userspace. On sync I/O this will include the completion of the > request as sync I/O will wait for the request to land in pagecache. On > asynchronous I/O this will be really fast. > > clat: This is the time to complete handling the I/O request. Then it is at > least in the pagecache on buffered I/O. > > lat: The time it takes till the request has been processed. The HOWTO says: > "This is the time from when IO leaves fio and when it gets completed." > > So how is that completion different from the other completion in clat? […] > Reads: > clat (usec): min=189 , max=954818 , avg=5423.72, stdev=21529.85 > lat (usec): min=190 , max=954818 , avg=5423.90, stdev=21529.85 > > > Writes: > clat (usec): min=3 , max=2391.5K, avg=180.47, stdev=8936.82 > lat (usec): min=4 , max=2391.5K, avg=180.59, stdev=8936.82 > > > So whats the difference here? Is > > lat = slat + clat? Could be (from another job with iodepth 64) write: slat (usec): min=5 , max=753280 , avg=190.49, stdev=8787.41 clat (usec): min=677 , max=2178.2K, avg=317831.81, stdev=282569.45 lat (usec): min=715 , max=2178.2K, avg=318023.20, stdev=282631.85 read: slat (usec): min=5 , max=139 , avg=22.73, stdev= 5.52 clat (msec): min=8 , max=1756 , avg=203.10, stdev=174.58 lat (msec): min=8 , max=1756 , avg=203.13, stdev=174.58 Hmmm, on read averages don't add up. > Why did you drop slat from output? Forget this one. It obviously is there. Ciao, -- Martin Steigerwald - teamix GmbH - http://www.teamix.de gpg: 19E3 8D42 896F D004 08AC A0CA 1E10 C593 0399 AE90 -- 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
