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Message-ID: <CAJvTdKmJr70DYAjDs-38PzEUSNpn1ncXxR_csFw3a724egHnZQ@mail.gmail.com>
Date: Thu, 14 May 2015 02:36:58 -0400
From: Len Brown <lenb@...nel.org>
To: Ingo Molnar <mingo@...nel.org>
Cc: Jan H. Schönherr <jschoenh@...zon.de>,
Thomas Gleixner <tglx@...utronix.de>, X86 ML <x86@...nel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Anthony Liguori <aliguori@...zon.com>,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>, Tim Deegan <tim@....org>,
Gang Wei <gang.wei@...el.com>,
Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] x86: skip delays during SMP initialization similar to Xen
> [ 0.404369] x86: Booting SMP configuration:
...
> [ 2.737884] x86: Booted up 4 nodes, 120 CPUs
> [ 2.743758] smpboot: Total of 120 processors activated (671097.18 BogoMIPS)
>
> (2.743758-0.404369) = 2.339389 for all 119 processors
> /119 = .01965873109243697478 - lets call it 19ms each
For the record, the same (bare metal) box running latest tip boots
10ms/processor quicker
than upstream Linux, as expected. So this 120 processor box now
boots 1.19 seconds faster, in total.
[ 0.415969] x86: Booting SMP configuration:
...
[ 1.553658] x86: Booted up 4 nodes, 120 CPUs
[ 1.559173] smpboot: Total of 120 processors activated (671182.14 BogoMIPS)
1.553658-0.415969 = 1.137689 - seconds to bring 119 processors on-line.
./119 = .00956041176470588235 -- 9.5ms per processor, down from 19.
BTW. this time can be reduced by 7% (113 ms) by deleting announce_cpu():
[ 1.445815] x86: Booted up 4 nodes, 120 CPUs
cheers,
Len Brown, Intel Open Source Technology Center
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