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x86: Reduce clock calibration time during slave cpu startup

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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 <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: John Stultz <[email protected]>
[fix CONFIG_SMP=n build]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Jack Steiner 2011-11-15 15:33:56 -08:00 • committed by Ingo Molnar
commit b565201cf7
3 changed files with 46 additions and 5 deletions
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15
init/calibrate.c
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@ -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 "