linux-kernel - RE: [PATCH] [RFC] ondemand governor: dynamic cpufreq scaling with different CPUs

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Date:	Mon, 01 Aug 2011 10:51:38 -0400 (EDT)
From:	Len Brown <lenb@...nel.org>
To:	"Yung, Winson W" <winson.w.yung@...el.com>
Cc:	Venkatesh Pallipadi <venki@...gle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Van De Ven, Arjan" <arjan.van.de.ven@...el.com>,
	"Kanigeri, Hari K" <hari.k.kanigeri@...el.com>
Subject: RE: [PATCH] [RFC] ondemand governor: dynamic cpufreq scaling with
 different CPUs

Re: software vs hardware coordination

Speaking for Intel, everything we make, from hand-sets to supercomputers
supports hardware coorination.

Think about it -- if we did not, then we would not be able
to support a legacy OS that doesn't know how to do SW coordination.

HW coordiation is the simplest thing for the SW because
SW doesn't have to know anything at all about topology constraints.
It is also the simplest thing for the BIOS, which doesn't have
to correctly describe topology.

Yes, there is an MSR bit that the BIOS can flip to disable
HW coordination.  90% of the time that bit is set it is a BIOS bug.
eg. the bit is set, but the BIOS fails to properly set up the
ACPI tables to properly enable SW coordination, resulting
in a system with really strange performance issues.

Indeed, I proposed before, and I will propose again that
the underlying ACPI _PSD support behind SW coordination
be completely removed from Linux.

Venki,
I recall that you mentioned one platform that depends on it --
and I'd  like to understand that issue and address it with a quirk
rather than expose all systems to BIOS bugs due to bogus _PSD support.

Winston,
Your system is running in SW coordination mode?
What do you see if you run with the patch below?
I'd be intersted to see the output from adpidump for your system.

thanks,
-Len Brown
Intel Open Source Technology Center

---
diff --git a/include/acpi/pdc_intel.h b/include/acpi/pdc_intel.h
index 552637b..d081595 100644
--- a/include/acpi/pdc_intel.h
+++ b/include/acpi/pdc_intel.h
@@ -22,7 +22,6 @@

 #define ACPI_PDC_EST_CAPABILITY_SWSMP	(ACPI_PDC_SMP_C1PT | \
 					 ACPI_PDC_C_C1_HALT | \
-					 ACPI_PDC_SMP_P_SWCOORD | \
 					 ACPI_PDC_SMP_P_HWCOORD | \
 					 ACPI_PDC_P_FFH)

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