linux-kernel - Re: [PATCH] x86, vsmp: Remove is_vsmp_box() from apic_is_clustered

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Date:	Mon, 23 Jun 2014 07:18:03 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	Oren Twaig <oren@...lemp.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	David Rientjes <rientjes@...gle.com>,
	Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>,
	Richard Weinberger <richard@....at>, x86@...nel.org,
	linux-kernel@...r.kernel.org, Shai Fultheim <shai@...lemp.com>
Subject: Re: [PATCH] x86, vsmp: Remove is_vsmp_box() from
 apic_is_clustered_box()

On Mon, Jun 23, 2014 at 08:35:14AM +0300, Oren Twaig wrote:
> Remove invalid code which caused TSC to be declared as "unstable" on vSMP
> Foundation box even if it was stable and let the kernel decide for itself.
> 
> When a vSMP Foundation box is detected, the function apic_cluster_num() counts
> the number of APIC clusters found. If more than one found, a multi board
> configuration is assumed, and TSC marked as unstable. This behavior is
> incorrect as vSMP Foundation may use processors from single node only, attached
> to memory of other nodes - and such node may have more than one APIC cluster
> (typically any recent intel box has more than single APIC_CLUSTERID(x)).
> 
> To fix this, we simply remove the code which detects a vSMP Foundation box and
> affects apic_is_clusted_box() return value. This can be done because later the
> kernel checks by itself if the TSC is stable using the
> check_tsc_sync_[source|target]() functions and marks TSC as unstable if needed.

Looks good to me. Yes the APIC cluster check is obsolete.

-andi
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