Date: Fri, 01 Mar 2002 00:26:06 +0100 From: "Rogier R. Mulhuijzen" <drwilco@drwilco.net> To: "Frost, Stephen C" <stephen.c.frost@intel.com>, "'freebsd-questions@freebsd.org'" <freebsd-questions@FreeBSD.ORG>, "'freebsd-hackers@freebsd.org'" <freebsd-hackers@FreeBSD.ORG>, "'freebsd-smp@freebsd.org'" <freebsd-smp@FreeBSD.ORG> Cc: "Frost, Stephen C" <stephen.c.frost@intel.com> Subject: RE: FreeBSD, SMP and Performance Speeds? Message-ID: <5.1.0.14.0.20020301001536.01cd5610@mail.drwilco.net> In-Reply-To: <B9ECACBD6885D5119ADC00508B68C1EA0288A6E9@orsmsx107.jf.inte l.com>
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>Regarding my SMP query, Doc asks:
> > What sort of throughput? What sort of processes are you
> > running? Do you
> > actually have multiple processes fighting for CPU?
>
>Yes, I'm using netperf, iperf or nttcp to measure TCP throughput using the
>server (the box in question) in response to ten simultaneous clients.
>Chariot allegedly did not show the performance hit. But then, even
>measuring the process time to run a single simple script shows ~half the
>speed with SMP enabled.
I'm no expert but I'm going to have a shot at this anyways. Comments are
welcome. =)
When you run a benchmark or a process where network performance is the
bottleneck instead of CPU time, you're not going to have SMP help you at
all. Currently in the 4.X kernels the kernel can run on only one CPU at a
given time. That means that when raw network performance is the bottleneck
only one CPU is actually doing the work, and running in SMP mode gives you
a lot of overhead.
The same is true for a situation where a single single-threaded process is
involved. A single-threaded process can only run on one CPU at a given
time, so having a 2nd CPU only adds overhead.
Have you tried running 4 jobs simultaneously and timing that?
So what sort of application are you using exactly, is it multi-process,
multithreaded, CPU intensive, network intensive? Where do you think the
bottleneck in the performance lies at this moment?
Doc
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