linux-kernel - Re: [PATCH] x86: use dmi check in apic_is

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Date:	Mon, 27 Apr 2009 16:30:47 -0700
From:	Ravikiran G Thirumalai <kiran@...lex86.org>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: use dmi check in apic_is_clustered with 64bit

On Sun, Apr 26, 2009 at 11:39:38PM -0700, Yinghai Lu wrote:
>
>will have system with 2 and more sockets 8cores/2thread.
>do treat them as multi chassis.
>
>use dmi check instead.
>
>[ Impact: do not make unstable TSC on wrongly ]
>
>Signed-off-by: Yinghai Lu <yinghai@...nel.org>
>

The patch looks good.
Just one minor observation -- apic_is_clustered_box()
is used only to check if tscs are synced.  It is not used elsewhere. Since
the routine is not actually checking if the box uses clustered apic --
rather the routine is used to determine if tsc's are synced are not, the name
could be changed appropriately I guess?

...
>+}
>+
>+/*
>+ * apic_is_clustered_box() -- Check if we can expect good TSC
>+ *
>+ * Thus far, the major user of this is IBM's Summit2 series:
>+ * Clustered boxes may have un-synced TSC problems if they are
>+ * multi-chassis.
>+ * Use DMI to check them
>+ */
>+__cpuinit int apic_is_clustered_box(void)
>+{
>+	dmi_check_multi();
>+	if (multi)
> 		return 1;
> 
>+	if (!is_vsmp_box())
>+		return 0;
>+
> 	/*
>-	 * If clusters > 2, then should be multi-chassis.
>-	 * May have to revisit this when multi-core + hyperthreaded CPUs come
>-	 * out, but AFAIK this will work even for them.
>+	 * ScaleMP vSMPowered boxes have one cluster per board and TSCs are
>+	 * not guaranteed to be synced between boards
> 	 */
>-	return (clusters > 2);
>+	if (apic_cluster_num() > 1)
>+		return 1;
>+
>+	return 0;
> }

...
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