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Re: [SLUG] uptime and multicore/multithreaded cpu's
- To: SLUG <slug@xxxxxxxxxxx>
- Subject: Re: [SLUG] uptime and multicore/multithreaded cpu's
- From: "Amos Shapira" <amos.shapira@xxxxxxxxx>
- Date: Thu, 24 Apr 2008 21:47:28 +1000
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On Wed, Apr 23, 2008 at 11:33 PM, Sonia Hamilton <sonia@xxxxxxxxxxxx> wrote:
> A question about uptime. My understanding of the load average figures is
> that a figure less than 2.0 on a 2 CPU machine means the CPUs don't have
> more work than they can keep up with (on average).
> How is this figure (1 per CPU) affected on multicore CPUs? What about
> multi-threaded CPU's?
As far as I remember, back when multi-threading just popped up (before
multi-core came) the word was to regard each thread as a CPU for load
average proposes, even though they were running on the same CPU.
The rule of thumb I inherited decades ago and always worked for me
when I cared about it, is to feel ok with up to 2xCPU cores (i.e. two
processes per core/thread/whatever), AfC's anecdote about Amazon
specific case aside.
The funny thing these days is that with the amount of cores you can
put on single boards today it's easy to clog the data paths (bus,
memory, disks, network) so don't forget to look at these too.