jeffr_tech (jeffr_tech ) wrote,

More subjective scheduler tests.

So I've just installed fedora core 7 on my laptop so I can do a side by side comparison of scheduler performance. The test I like to do with ULE is to make -j64 kernel while playing a dvd with mplayer and browsing the web. I have verified that make -j64 in the base directory of the linux kernel gets the load average up to the same level. The actual source involved matters little. Both systems are using a gcc 4.x compiler. The laptop is an IBM T42 with a 1.8ghz PentiumM,2 gigabytes of ram, and a 7200 rpm drive.

With the FreeBSD 7.0 configured without debugging options INVARIANTS and WITNESS, but with SCHED_ULE, I get no skipping or glitching of any kind.

With the O(1) scheduler in the default fedora core 7 kernel I get intermittent skipping but it's generally pretty tolerable.

I installed a 2.6.23-pre7 kernel built with 'make defconfig'. Feel free to suggest configuration options that may be relevant. At -j64 the ui was basically unusable. At -j4 it skipped more than the older kernel using -j64. It is my understanding that this is using the CFS scheduler.

I must say that in general the linux experience was very good. The installer was easy enough, although neither it or the installed system seemed to detect my atheros wireless card. I didn't care to futz with it so I just plugged it into my switch directly. It sure looked pretty otherwise. Maybe I'll try PC-BSD when they update to 7.0.

The issue with CFS is that the simple algorithm works very well as long as your interactive tasks consume less cpu in proportion to the other tasks. So for example mplayer takes 10% of the cpu playing a dvd on my machine. If you have 9 cpu hogs and mplayer running, without any information other than runtime or %cpu you can't distinguish between them.

Whether this is an important workload or not is subject to debate.
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