On Monday 09 April 2007 22:39, Mike Galbraith wrote: > On Mon, 2007-04-09 at 07:38 +0200, Mike Galbraith wrote: > > > I don't think you can have very much effect on latency using nice with > > SD once the CPU is fully utilized. See below. > > > > /* > > * This contains a bitmap for each dynamic priority level with empty slots > > * for the valid priorities each different nice level can have. It allows > > * us to stagger the slots where differing priorities run in a way that > > * keeps latency differences between different nice levels at a minimum. > > * ie, where 0 means a slot for that priority, priority running from left to > > * right: > > * nice -20 0000000000000000000000000000000000000000 > > * nice -10 1001000100100010001001000100010010001000 > > * nice 0 0101010101010101010101010101010101010101 > > * nice 5 1101011010110101101011010110101101011011 > > * nice 10 0110111011011101110110111011101101110111 > > * nice 15 0111110111111011111101111101111110111111 > > * nice 19 1111111111111111111011111111111111111111 > > */ > > > > Nice allocates bandwidth, but as long as the CPU is busy, tasks always > > proceed downward in priority until they hit the expired array. That's > > the design. > > There's another aspect of this that may require some thought - kernel > threads. As load increases, so does rotation length. Would you really > want CPU hogs routinely preempting house-keepers under load?
SD has a schedule batch nice level. This is good for tasks that want lots of cpu when they can get it. If you overload your cpu I expect the box to slow down - including kernel threads. If really required they can be started with a higher priority... Ed - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
