From 279f1461432ccdec0b98c0bcbe0a8e2c0f6fdda5 Mon Sep 17 00:00:00 2001 From: Suresh Siddha Date: Mon, 22 Oct 2012 14:37:58 -0700 Subject: x86: apic: Use tsc deadline for oneshot when available If the TSC deadline mode is supported, LAPIC timer one-shot mode can be implemented using IA32_TSC_DEADLINE MSR. An interrupt will be generated when the TSC value equals or exceeds the value in the IA32_TSC_DEADLINE MSR. This enables us to skip the APIC calibration during boot. Also, in xapic mode, this enables us to skip the uncached apic access to re-arm the APIC timer. As this timer ticks at the high frequency TSC rate, we use the TSC_DIVISOR (32) to work with the 32-bit restrictions in the clockevent API's to avoid 64-bit divides etc (frequency is u32 and "unsigned long" in the set_next_event(), max_delta limits the next event to 32-bit for 32-bit kernel). Signed-off-by: Suresh Siddha Cc: venki@google.com Cc: len.brown@intel.com Link: http://lkml.kernel.org/r/1350941878.6017.31.camel@sbsiddha-desk.sc.intel.com Signed-off-by: Thomas Gleixner --- Documentation/kernel-parameters.txt | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'Documentation/kernel-parameters.txt') diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 9776f068306..4aa9ca0de63 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -1304,6 +1304,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted. lapic [X86-32,APIC] Enable the local APIC even if BIOS disabled it. + lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline + value for LAPIC timer one-shot implementation. Default + back to the programmable timer unit in the LAPIC. + lapic_timer_c2_ok [X86,APIC] trust the local apic timer in C2 power state. -- cgit v1.2.3