G'Day Russ, On Tue, Feb 05, 2008 at 07:51:38AM -0800, Russ wrote: > Hi; > > I'm trying to track I/O performance of an application accessing a solid state > storage device which should have sub 15us latencies...I was looking at using > iosnoop from the dtrace toolkit, as iostat is no use at this level of > granularity. > > Unfortunately, the app is very I/O heavy and after a couple of seconds the > I/O snoop craps out, giving me thousands of dynamic variable drops. > > Is there any way to fix this, or am I simply using iosnoop for something it > can't handle?
Sub 15us is starting to get pretty fast (until CPUs become faster, I wouldn't trust measuring something sub 1us). You can try tuning DTrace to avoid the dynamic variable drops (dynvarsize is the tunable), however there might be an easier way: You said that you started with iostat? Stats such as those that provide "asvc_t" are stored in a higher resolution than iostat prints (stored as hrtime_t). If they were the metrics of interest, then you can dig the original values from kstat and produce high resolution versions of wsvc_t, asvc_t, %b, etc. We discussed iostat calculations, kstat, and scripting with kstat in the "Solaris Performance and Tools" book. Brendan -- Brendan [CA, USA] _______________________________________________ dtrace-discuss mailing list [email protected]
