On Fri, 2006-06-23 at 12:12 +0200, Pieter Palmers wrote: > Lee Revell wrote: > > >On Fri, 2006-06-23 at 09:44 +0930, Jonathan Woithe wrote: > > > > > >>Despite what the log says, this was running a 2.0 GHz "Dothan" > >>Centrino CPU. Kernel was 2.6.16-rt25, distro was Slackware 10.2. Both > >>the stress tester and the monitor were run with RT privilege access. > >>The firewire interface used has a TI OHCI chipset. > >> > >>I apologise that the run was particularly short and that therefore the > >>statistics aren't particularly good, but it does seem to confirm the > >>observations you made on your machine. The large latencies only occur > >>when the stress tester is running. > >> > >> > > > >What if you run the latency tester at RT priority 99? Testing at 80 is > >not particularly useful. > > > > > Why not? > > If the 1394 test user thread has a lower priority, and the ohci1394 irq > priority is also lower, there is no reason for the latency tester to be > preempted by them. >
Because as you stated below the system timer runs at a higher priority by default. I wanted to rule out preemption by the system timer thread. > >If anything else is running at 99, what happens if you lower those other > >processes to 98? > > > > > I'll have to recheck, but if I remember correcly I have done this > experiment. The only thing at 99 is the system timer. I tried giving it > a lower priority than the latency test thread, which didn't change anything. > OK thanks, that answers my question. > Pieter >
