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David Schwartz wrote: > Bill Davidsen wrote:> > >>I agree for giving a process more than a fair share, but I don't think >>"latency" is the best term for what you describe later. If you think of >>latency as the time between a process unblocking and the time when it >>gets CPU, that is a more traditional interpretation. I'm not really sure >>latency and CPU-starved are compatible.> > > For CPU-starvation, I think 'nice' is always going to be the fix. If you > want a process to get more than its 'fair share' of the CPU, you have to ask > for that. I think the scheduler should be fair by default. > > However, cleverness in the scheduler with latency can make things better > without being unfair to anyone. It's perfectly fair for a task that has been > blocked for awhile to pre-empt a CPU-limited task when it unblocks. > > What I'm arguing is that if your task is CPU-limited and the scheduler is > fair, that's your fault -- nice it. If your task is suffering from poor > latency, and it's using less than its fair share of the CPU (because it is > not CPU-limited), that is something the scheduler can be smarter about. Agreed. That's what I've been saying for years (since early 2.6 when we had all those scheduler troubles and I started nicksched). > Honestly, I have always been against aggressive pre-emption. I think as CPUs > get faster and timeslices get shorter, it makes less and less sense. In many I think scheduler timeslices actually shouldn't really be getting shorter. While I found it is quite easy to get good interactivity with a pretty dumb scheduler and tiny timeslices (at least until load ramps up enough that the "off-time" for your critical processes builds up too much), I think we want to aim for large timeslices. CPU caches are still getting bigger, and I don't think misses are getting cheaper (especially if you consider multi core). Also, the energy cost of a memory access is much higher even if hardware or software is able to hide the latency. -- SUSE Labs, Novell Inc. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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