linux-kernel - [PATCH] Preset lpj values when on VMware.

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Date:	Mon, 02 Aug 2010 16:10:37 -0700
From:	Alok Kataria <akataria@...are.com>
To:	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	the arch/x86 maintainers <x86@...nel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, Dan Hecht <dhecht@...are.com>,
	gcosta@...hat.com
Subject: [PATCH] Preset lpj values when on VMware.

Please consider the patch below for the tip tree. Thanks !

--
When running on VMware's platform, we have seen situations where
the AP's try to calibrate the lpj values and fail to get good calibration
runs becasue of timing issues. As a result delays don't work correctly
on all cpus. 
The solutions is to set preset_lpj value based on the current tsc frequency
value. This is similar to what KVM does as well.

Signed-off-by: Alok N Kataria <akataria@...are.com>

Index: linux-x86-tree.git/arch/x86/kernel/cpu/vmware.c
===================================================================
--- linux-x86-tree.git.orig/arch/x86/kernel/cpu/vmware.c	2010-08-02 15:43:28.000000000 -0700
+++ linux-x86-tree.git/arch/x86/kernel/cpu/vmware.c	2010-08-02 15:43:37.000000000 -0700
@@ -51,7 +51,7 @@ static inline int __vmware_platform(void
 
 static unsigned long vmware_get_tsc_khz(void)
 {
-	uint64_t tsc_hz;
+	uint64_t tsc_hz, lpj;
 	uint32_t eax, ebx, ecx, edx;
 
 	VMWARE_PORT(GETHZ, eax, ebx, ecx, edx);
@@ -62,6 +62,13 @@ static unsigned long vmware_get_tsc_khz(
 	printk(KERN_INFO "TSC freq read from hypervisor : %lu.%03lu MHz\n",
 			 (unsigned long) tsc_hz / 1000,
 			 (unsigned long) tsc_hz % 1000);
+
+	if (!preset_lpj) {
+		lpj = ((u64)tsc_hz * 1000);
+		do_div(lpj, HZ);
+		preset_lpj = lpj;
+	}
+
 	return tsc_hz;
 }
 


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