On Fri, 2013-05-03 at 13:57 +0800, Michael Wang wrote: > Hi, Mike > > Thanks for your reply. > > On 05/03/2013 01:01 PM, Mike Galbraith wrote: > [snip] > >> > >> If this approach caused any concerns, please let me know ;-) > > > > I wonder if throttling on failure is the way to go. Note the minimal > > gain for pgbench with the default 1ms throttle interval. It's not very > > effective out of the box for the load type it's targeted to help, and > > people generally don't twiddle scheduler knobs. If you throttle on > > success, you directly restrict migration frequency without that being > > affected by what other tasks are doing. Seems that would be a bit more > > effective. > > This is a good timing to make some conclusion for this problem ;-) > > Let's suppose when wake-affine failed, next time slice got a higher > failure chance, then whether throttle on failure could be the question like: > > throttle interval should cover more failure timing > or more success timing? > > Obviously we should cover more failure timing, since it's just wasting > cycle and change nothing. > > However, I used to concern about the damage of succeed wake-affine at > that rapid, sure it also contain the benefit, but which one is bigger? > > Now if we look at the RFC version which throttle on succeed, for > pgbench, we could find that the default 1ms benefit is < 5%, while the > current version which throttle on failure bring 7% at most.
OK, so scratch that thought. Would still be good to find a dirt simple dirt cheap way to increase effectiveness a bit, and eliminate the knob. Until a better idea comes along, this helps pgbench some, and will also help fast movers ala tbench on AMD, where select_idle_sibling() wasn't particularly wonderful per my measurements. -Mike -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
