Messages in this thread | ![/](/images/icornerl.gif) | | Date | Tue, 16 Dec 2003 00:37:46 +0100 | From | Andrea Arcangeli <> | Subject | Re: 2.6.0-test9 - poor swap performance on low end machines |
| |
On Mon, Dec 15, 2003 at 03:31:22PM -0800, Andrew Morton wrote: > Single-threaded qsbench is OK on 2.6. Last time I looked it was a little > quicker than 2.4. It's when you go to multiple qsbench instances that > everything goes to crap. > > It's interesting to watch the `top' output during the run. In 2.4 you see > three qsbench instances have consumed 0.1 seconds CPU and the fourth has > consumed 45 seconds and then exits. > > In 2.6 all four processes consume CPU at the same rate. Really, really > slowly.
sounds good, so this seems only a fariness issue. 2.6 is more fair but fariness in this case means much inferior performance.
The reason 2.4 runs faster could be a more aggressive "young" pagetable heuristic via the swap_out clock algorithm. as soon as one program grows a bit its rss, it will run for longer, and the longer it runs the more pages it marks "young" during a clock scan, and the more pages it marks young the bigger it will grow. This keeps going until it's the by far biggest task and takes almost all available cpu. This is optimal for performance, but not optimal for fariness. So 2.6 may be better or worse depending if fariness payoffs or not, obviously in qsbench it doesn't since it's not even measured. - 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/
| ![\](/images/icornerr.gif) |