Re: BFS vs. mainline scheduler benchmarks and measurements
From: Nikos Chantziaras
Date: Tue Sep 08 2009 - 18:53:56 EST
On 09/08/2009 05:20 PM, Arjan van de Ven wrote:
On Tue, 08 Sep 2009 13:13:34 +0300
Nikos Chantziaras<realnc@xxxxxxxx> wrote:
On 09/08/2009 11:38 AM, Arjan van de Ven wrote:
On Tue, 08 Sep 2009 10:19:06 +0300
Nikos Chantziaras<realnc@xxxxxxxx> wrote:
latencytop has this to say:
http://foss.math.aegean.gr/~realnc/pics/latop1.png
Though I don't really understand what this tool is trying to tell
me, I hope someone does.
despite the untranslated content, it is clear that you have
scheduler delays (either due to scheduler bugs or cpu contention)
of upto 68 msecs... Second in line is your binary AMD graphics
driver that is chewing up 14% of your total latency...
I've now used a correctly installed and up-to-date version of
latencytop and repeated the test. Also, I got rid of AMD's binary
blob and used kernel DRM drivers for my graphics card to throw fglrx
out of the equation (which btw didn't help; the exact same problems
occur).
Here the result:
http://foss.math.aegean.gr/~realnc/pics/latop2.png
Again: this is on an Intel Core 2 Duo CPU.
so we finally have objective numbers!
now the interesting part is also WHERE the latency hits. Because
fundamentally, if you oversubscribe the CPU, you WILL get scheduling
latency.. simply you have more to run than there is CPU.
Sounds plausible. However, with mainline this latency is very, very
noticeable. With BFS I need to look really hard to detect it or do
outright silly things, like a "make -j50". (At first I wrote "-j20"
here but then went ahead an tested it just for kicks, and BFS would
still let me use the GUI smoothly, LOL. So then I corrected it to
"-j50"...)
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