On Saturday 21 April 2007 22:12, Willy Tarreau wrote: > Hi Ingo, Hi Con, > > I promised to perform some tests on your code. I'm short in time right now, > but I observed behaviours that should be commented on. > > 1) machine : dual athlon 1533 MHz, 1G RAM, kernel 2.6.21-rc7 + either > scheduler Test: ./ocbench -R 250000 -S 750000 -x 8 -y 8 > ocbench: http://linux.1wt.eu/sched/ > > 2) SD-0.44 > > Feels good, but becomes jerky at moderately high loads. I've started > 64 ocbench with a 250 ms busy loop and 750 ms sleep time. The system > always responds correctly but under X, mouse jumps quite a bit and > typing in xterm or even text console feels slightly jerky. The CPU is > not completely used, and the load varies a lot (see below). However, > the load is shared equally between all 64 ocbench, and they do not > deviate even after 4000 iterations. X uses less than 1% CPU during > those tests. > > Here's the vmstat output : [snip]
> 3) CFS-v4 > > Feels even better, mouse movements are very smooth even under high load. > I noticed that X gets reniced to -19 with this scheduler. I've not looked > at the code yet but this looked suspicious to me. I've reniced it to 0 > and it did not change any behaviour. Still very good. The 64 ocbench share > equal CPU time and show exact same progress after 2000 iterations. The CPU > load is more smoothly spread according to vmstat, and there's no idle (see > below). BUT I now think it was wrong to let new processes start with no > timeslice at all, because it can take tens of seconds to start a new > process when only 64 ocbench are there. Simply starting "killall ocbench" > takes about 10 seconds. On a smaller machine (VIA C3-533), it took me more > than one minute to do "su -", even from console, so that's not X. BTW, X > uses less than 1% CPU during those tests. > > [EMAIL PROTECTED]:~$ vmstat 1 [snip] > 4) first impressions > > I think that CFS is based on a more promising concept but is less mature > and is dangerous right now with certain workloads. SD shows some strange > behaviours like not using all CPU available and a little jerkyness, but is > more robust and may be the less risky solution for a first step towards > a better scheduler in mainline, but it may also probably be the last O(1) > scheduler, which may be replaced sometime later when CFS (or any other one) > shows at the same time the smoothness of CFS and the robustness of SD. I assumed from your description that you were running X nice 0 during all this testing and left the tunables from both SD and CFS at their defaults; this tends to have the effective equivalent of "timeslice" in CFS smaller than SD. > I'm sorry not to spend more time on them right now, I hope that other > people will do. Thanks for that interesting testing you've done. The fluctuating cpu load and the apparently high idle time means there is almost certainly a bug still in the cpu accounting I do in update_cpu_clock. It looks suspicious to me already on just my first glance. Fortunately the throughput does not appear to be adversely affected on other benchmarks so I suspect it's lying about the idle time and it's not really there. Which means it's likely also accounting the cpu time wrongly. Which also means there's something I can fix and improve SD further. Great stuff, thanks! -- -ck - 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/