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authorLinus Torvalds <torvalds@linux-foundation.org>2012-01-11 19:13:40 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2012-01-11 19:13:40 -0800
commit9fc5c3e3237e02a94f41cd1d2b4291593d29791d (patch)
treec8823725b10bd4d36e9311ea392dfdecb4db7974 /arch/x86/kernel/tsc.c
parent541048a1d31399ccdda27346a37eae4a2ad55186 (diff)
parent7c9c3a1e5fc8728e948b8fa3cbcfcfb86db3afda (diff)
Merge branch 'x86-platform-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
* 'x86-platform-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: x86/intel config: Fix the APB_TIMER selection x86/mrst: Add additional debug prints for pb_keys x86/intel config: Revamp configuration to allow for Moorestown and Medfield x86/intel/scu/ipc: Match the changes in the x86 configuration x86/apb: Fix configuration constraints x86: Fix INTEL_MID silly x86/Kconfig: Cyclone-timer depends on x86-summit x86: Reduce clock calibration time during slave cpu startup x86/config: Revamp configuration for MID devices x86/sfi: Kill the IRQ as id hack
Diffstat (limited to 'arch/x86/kernel/tsc.c')
-rw-r--r--arch/x86/kernel/tsc.c20
1 files changed, 20 insertions, 0 deletions
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 2c9cf0fd78f5..c0dd5b603749 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -995,3 +995,23 @@ void __init tsc_init(void)
check_system_tsc_reliable();
}
+#ifdef CONFIG_SMP
+/*
+ * If we have a constant TSC and are using the TSC for the delay loop,
+ * we can skip clock calibration if another cpu in the same socket has already
+ * been calibrated. This assumes that CONSTANT_TSC applies to all
+ * cpus in the socket - this should be a safe assumption.
+ */
+unsigned long __cpuinit calibrate_delay_is_known(void)
+{
+ int i, cpu = smp_processor_id();
+
+ if (!tsc_disabled && !cpu_has(&cpu_data(cpu), X86_FEATURE_CONSTANT_TSC))
+ return 0;
+
+ for_each_online_cpu(i)
+ if (cpu_data(i).phys_proc_id == cpu_data(cpu).phys_proc_id)
+ return cpu_data(i).loops_per_jiffy;
+ return 0;
+}
+#endif