Date: Fri, 01 Dec 2006 13:04:25 +0100 From: Ivan Voras <ivoras@fer.hr> To: Robert Watson <rwatson@FreeBSD.org> Cc: freebsd-arch@FreeBSD.org Subject: Re: What is the PREEMPTION option good for? Message-ID: <45701A49.5020809@fer.hr> In-Reply-To: <20061128142218.P44465@fledge.watson.org> References: <20061119041421.I16763@delplex.bde.org> <ejnvfo$tv2$1@sea.gmane.org> <ek4gc8$492$1@sea.gmane.org> <20061126174041.V83346@fledge.watson.org> <ekckpt$4h6$1@sea.gmane.org> <20061128142218.P44465@fledge.watson.org>
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Robert Watson wrote:
>
> They're independent twiddles, and can be frobbed separately. If you can
> easily measure performance in the different configurations, seeing a
> table of permutations and results would be very nice to see what happens
> :-).
Ok, this is what I found:
- ipiwakeup doesn't produce differences as calculated by ministat
- turning off preemption produces visible differences, which are
calculated by ministat to be upto 10%.
x nopreempt+ipiwakeup
+ preempt+ipiwakeup
+--------------------------------------------------------------------------+
|+ + + + x x xx xx x|
| |___________A__M________| |______MA_______| |
+--------------------------------------------------------------------------+
N Min Max Median Avg Stddev
x 7 99.92 104.19 101.48 101.78429 1.4606717
+ 4 90.5 95.78 94.12 93.53 2.2081365
Difference at 95.0% confidence
-8.25429 +/- 2.4751
-8.10959% +/- 2.43172%
(Student's t, pooled s = 1.74576)
Sorry about the small number of samples - these are collected from the
system in the same state and product version (the machine was otherwise
idle, etc.), but the difference is always present - I've run simpler
benchmarks every few days since the discussion started and it's there.
This is on a low-end dual core Xeon (i.e. one socket, two cores, no HT),
enough RAM not to swap, requests/second with high concurrency on a web
application that does a lot of IPC to database & cache engines through
both TCP/localhost and unix sockets.
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