Messages in this thread | | | Date | Sat, 19 Sep 2009 20:43:51 +0200 | From | Felix Fietkau <> | Subject | Re: BFS vs. mainline scheduler benchmarks and measurements |
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Ingo Molnar wrote: > * Felix Fietkau <nbd@openwrt.org> wrote: > >> Ingo Molnar wrote: >> > Well that's a really memory constrained MIPS device with like 16 MB of >> > RAM or so? So having effects from small things like changing details in >> > a kernel image is entirely plausible. >> >> Normally changing small details doesn't have much of an effect. While >> 16 MB is indeed not that much, we do usually have around 8 MB free >> with a full user space running. Changes to other subsystems normally >> produce consistent and repeatable differences that seem entirely >> unrelated to memory use, so any measurable difference related to >> scheduler changes is unlikely to be related to the low amount of RAM. >> By the way, we do frequently also test the same software with devices >> that have more RAM, e.g. 32 or 64 MB and it usually behaves in a very >> similar way. > > Well, Michael Buesch posted vmstat results, and they show what i have > found with my x86 simulated reproducer as well (these are Michael's > numbers): > > procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu---- > r b swpd free buff cache si so bi bo in cs us sy id wa > 1 0 0 15892 1684 5868 0 0 0 0 268 6 31 69 0 0 > 1 0 0 15892 1684 5868 0 0 0 0 266 2 34 66 0 0 > 1 0 0 15892 1684 5868 0 0 0 0 266 6 33 67 0 0 > 1 0 0 15892 1684 5868 0 0 0 0 267 4 37 63 0 0 > 1 0 0 15892 1684 5868 0 0 0 0 267 6 34 66 0 0 > > on average 4 context switches _per second_. The scheduler is not a > factor on this box. > > Furthermore: > > | I'm currently unable to test BFS, because the device throws strange > | flash errors. Maybe the flash is broken :( > > So maybe those flash errors somehow impacted the measurements as well? I did some tests with BFS v230 vs CFS on Linux 2.6.30 on a different MIPS device (Atheros AR2317) with 180 MHz and 16 MB RAM. When running iperf tests, I consistently get the following results when running the transfer from the device to my laptop:
CFS: [ 5] 0.0-60.0 sec 107 MBytes 15.0 Mbits/sec BFS: [ 5] 0.0-60.0 sec 119 MBytes 16.6 Mbits/sec
The transfer speed from my laptop to the device are the same with BFS and CFS. I repeated the tests a few times just to be sure, and I will check vmstat later. The difference here cannot be flash related, as I ran a kernel image with the whole userland contained in initramfs. No on-flash filesystem was mounted or accessed.
- Felix
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