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Date: Mon, 28 Nov 2011 17:22:21 +0700
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Subject: Re: [gentoo-user] emerge -j, make -j and make -l
From: Pandu Poluan <pandu@poluan.info>
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On Mon, Nov 28, 2011 at 16:27, Neil Bothwick <neil@digimed.co.uk> wrote:
> On Mon, 28 Nov 2011 12:26:48 +0700, Pandu Poluan wrote:
>
>> Just in case anyone wonders where the multiplier "1.6" comes from:
>>
>> There had been a discussion somewhere (I forgot where exactly, sorry)
>> about load numbers. The final conclusion was that the ideal load number
>> for today's processors is 2*N, because with the out-of-order capability
>> of modern processors, two instructions can overlap in the pipeline, even
>> without hyperthreading.
>
> Is N the number of physical cores, or does it include hyperthreaded cores
> too?
>
And that... I forgot.
However, considering hyperthreading is just a 'trick' where a pair
threads of the same context can run together on a core, I'd wager that
N here should be considered as the physical core.
In other words, my guess is that 2*N is the "implicit hyperthreading"
performed by OOO processor cores. On hyperthreaded cores, the 2*N
ability of OOO processors is made "explicit".
TL;DR : 2*N for non-hyperthreaded cores, N for hyperthreaded cores.
(Disclaimer: Above is my pure speculation. Feel free to debunk it
based on your tests (: )
Rgds,
--=20
FdS Pandu E Poluan
~ IT Optimizer ~
=C2=A0=E2=80=A2 LOPSA Member #15248
=C2=A0=E2=80=A2 Blog : http://pepoluan.tumblr.com
=C2=A0=E2=80=A2 Linked-In : http://id.linkedin.com/in/pepoluan