On Wed, Nov 11, 2009 at 02:52:14PM -0800, Garrett D'Amore wrote: > Scott Rotondo wrote: > >Garrett D'Amore wrote: > >>As far as this case goes, I'd better like to understand why we needed > >>a new class, instead of just using SYS. > > > >That's the key question, which I haven't really seen anyone address in > >this PSARC email thread. However, you can find a high-level answer in > >CR 6806882: > > > >"The basic issue is that the SYS scheduling class was not designed for > >long-running CPU intensive workloads. We introduce a new SDC (System > >Duty Cycle) scheduling class, which adjusts its threads' priority in > >order to give them a specified percentage of the processor. > >It also gives them a scheduling quantum, which gives other threads at > >the same priority on the same CPU a chance to run." > > > > Scott > > > So my read of the above is that this is an attempt to give userland-like > scheduling properties to kernel threads (perhaps somewhat like the FX > class?). Which further underscores the fact that making this class > available to user threads is probably pointless.
See the big theory statement I attached in response; basically, we lower the priority to 0 whenever we're ahead of our duty cycle, which gives user threads a chance to use the CPU, preventing latency bubbles. Cheers, - jonathan
