linux-kernel - Re: native_cpu_up speed (Re: [PATCH] x86: skip delays during SMP initialization similar to Xen)

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Date:	Fri, 29 May 2015 10:04:43 +0200
From:	"Jan H. Schönherr" <jschoenh@...zon.de>
To:	Len Brown <lenb@...nel.org>, Ingo Molnar <mingo@...nel.org>
CC:	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: native_cpu_up speed (Re: [PATCH] x86: skip delays during SMP
 initialization similar to Xen)

On 05/29/2015 09:47 AM, Len Brown wrote:
> However, a clear pattern jumped out of the trace for how long
> the BSP waits for the AP to set itself in cpu_callin_mask.
> This is the time in start secondary where cpu_init() is running,
> up through smp_callin() is called.
>
> On the 1st package, each remote AP take 9 delays = 900 us to do this,
> whether they are new cores or HT siblings of cores already up.
> But the 1st processor on remote_packages_  aka nodes, takes 60,000 us
>
> No typo -- that is 60ms!

That does sound like calibrate_delay(), which "waits" for 5 * (10ms + 1 tick)
on each newly encountered package...

Regards
Jan
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