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authorJack Steiner <steiner@sgi.com>2011-11-15 15:33:56 -0800
committerIngo Molnar <mingo@elte.hu>2011-12-05 17:12:43 +0100
commitb565201cf75210614903ef2ae5917b4379681647 (patch)
tree6d28d33cf25a4fa47700b12d8e291886e1af195f
parent1ea7c6737c8f68453f55c894b3d07d7f48fcbef8 (diff)
downloadvexpress-lsk-b565201cf75210614903ef2ae5917b4379681647.tar.gz
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>
-rw-r--r--arch/x86/kernel/smpboot.c16
-rw-r--r--arch/x86/kernel/tsc.c20
-rw-r--r--init/calibrate.c15
3 files changed, 46 insertions, 5 deletions
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 9f548cb4a95..00eef55c832 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -207,23 +207,29 @@ static void __cpuinit smp_callin(void)
* Need to setup vector mappings before we enable interrupts.
*/
setup_vector_irq(smp_processor_id());
+
+ /*
+ * Save our processor parameters. Note: this information
+ * is needed for clock calibration.
+ */
+ smp_store_cpu_info(cpuid);
+
/*
* Get our bogomips.
+ * Update loops_per_jiffy in cpu_data. Previous call to
+ * smp_store_cpu_info() stored a value that is close but not as
+ * accurate as the value just calculated.
*
* Need to enable IRQs because it can take longer and then
* the NMI watchdog might kill us.
*/
local_irq_enable();
calibrate_delay();
+ cpu_data(cpuid).loops_per_jiffy = loops_per_jiffy;
local_irq_disable();
pr_debug("Stack at about %p\n", &cpuid);
/*
- * Save our processor parameters
- */
- smp_store_cpu_info(cpuid);
-
- /*
* This must be done before setting cpu_online_mask
* or calling notify_cpu_starting.
*/
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index db483369f10..490fb330be8 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
diff --git a/init/calibrate.c b/init/calibrate.c
index 24df7976816..5f117ca9e06 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 "