wio only makes sense on a uni-processor. Thats why it made sense in the very distant past, and stopped making sense a long time ago.
CPU's don't wait for io, processes do. Adrian On Sun, Aug 24, 2008 at 12:41 AM, Bert Miemietz <[EMAIL PROTECTED]> wrote: > Back in 2005 there was a short discussion about "Wait I/O Calculations". > Since the first contact with Solaris 10 I've been missing useful %wio values > and things > did not become better over the last years. Hope, you don't mind raising this > issue again. > > The basic statement was "%wio is a meaningless statistic ... we've removed > the statistic in Solaris 10. %wio will now always return zero." > > IMHO the creators of this "meaningless value" did have something in mind (all > SVR4 systems and most other UNIX-Systems _do_ maintain this "meaningless > value"). > I can agree with most arguments from the discussion in 2005. Above all a > certain amount of %wio doesn't say anything about IO problems or its nature. > If there are IO problems a process-/threadwise analysis (dtrace, prex ...) is > more useful. > > The %wio value is a percentage of time where "CPU is idle waiting for IO". In > other words: It gives us an idea of how much more CPU time could be spent for > calculations if the CPU(s) would not have to wait for IO with the programs > they are currently executing (load profile). Nothing more but nothing less!!! > As such this value gives us an excellent overall indicator of the > CPU/IO-subsystem balance related to the current load profile. > > To take one example from the discussion: >> A user would see 100% I/O wait in vmstat report when the CPU is idle >> and there's only one thread waiting for I/O, > This means faster program execution is blocked by waiting on IO-requests. If > this can be seen for a long time (and the program isn't changed) the most > promising way to make things faster is to care for faster IO. Detailed > analysis could be done with dtrace. >> he would also see 0% wait when there're 100 threads waiting for I/O >> but just one thread keeps the CPU busy at the same time, > This means: > a) The user is running Solaris 10 and has no useful wio value > or: > b) the IO system is fast enough to serve the CPU. If it was faster we would > see little effect only (compared to the situation above) since the program > would have to wait for CPU in case of IO returning faster. > > I see all the advantages of detailed statistics e. g. with dtrace but I > cannot see any advantage of removing the _useful_ %wio-value from kstat (sar > -d, mpstat ...). So I'd like to ask for re-insertion of this value. > > > This message posted from opensolaris.org > _______________________________________________ > perf-discuss mailing list > perf-discuss@opensolaris.org > _______________________________________________ perf-discuss mailing list perf-discuss@opensolaris.org
