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| author | Jack Steiner <steiner@sgi.com> | 2011-11-15 15:33:56 -0800 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2011-12-05 17:12:43 +0100 |
| commit | b565201cf75210614903ef2ae5917b4379681647 (patch) | |
| tree | 6d28d33cf25a4fa47700b12d8e291886e1af195f /init | |
| parent | 1ea7c6737c8f68453f55c894b3d07d7f48fcbef8 (diff) | |
| download | linux-b565201cf75210614903ef2ae5917b4379681647.tar.gz linux-b565201cf75210614903ef2ae5917b4379681647.tar.bz2 linux-b565201cf75210614903ef2ae5917b4379681647.zip | |
x86: Reduce clock calibration time during slave cpu startup
Reduce the startup time for slave cpus.
Adds hooks for an arch-specific function for clock calibration.
These hooks are used on x86. If a newly started cpu has the
same phys_proc_id as a core already active, uses the TSC for the
delay loop and has a CONSTANT_TSC, use the already-calculated
value of loops_per_jiffy.
This patch reduces the time required to start slave cpus on a
4096 cpu system from: 465 sec OLD 62 sec NEW
This reduces boot time on a 4096p system by almost 7 minutes.
Nice...
Signed-off-by: Jack Steiner <steiner@sgi.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: John Stultz <john.stultz@linaro.org>
[fix CONFIG_SMP=n build]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'init')
| -rw-r--r-- | init/calibrate.c | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/init/calibrate.c b/init/calibrate.c index 24df7976816c..5f117ca9e069 100644 --- a/init/calibrate.c +++ b/init/calibrate.c @@ -246,6 +246,19 @@ recalibrate: static DEFINE_PER_CPU(unsigned long, cpu_loops_per_jiffy) = { 0 }; +/* + * Check if cpu calibration delay is already known. For example, + * some processors with multi-core sockets may have all cores + * with the same calibration delay. + * + * Architectures should override this function if a faster calibration + * method is available. + */ +unsigned long __attribute__((weak)) __cpuinit calibrate_delay_is_known(void) +{ + return 0; +} + void __cpuinit calibrate_delay(void) { unsigned long lpj; @@ -265,6 +278,8 @@ void __cpuinit calibrate_delay(void) lpj = lpj_fine; pr_info("Calibrating delay loop (skipped), " "value calculated using timer frequency.. "); + } else if ((lpj = calibrate_delay_is_known())) { + ; } else if ((lpj = calibrate_delay_direct()) != 0) { if (!printed) pr_info("Calibrating delay using timer " |