The patch titled
Subject: x86: reduce clock calibration time during slave cpu startup
has been added to the -mm tree. Its filename is
x86-reduce-clock-calibration-time-during-slave-cpu-startup.patch
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------------------------------------------------------
From: Jack Steiner <steiner@xxxxxxx>
Subject: 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@xxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxx>
---
arch/x86/kernel/smpboot.c | 16 +++++++++++-----
arch/x86/kernel/tsc.c | 19 +++++++++++++++++++
init/calibrate.c | 15 +++++++++++++++
3 files changed, 45 insertions(+), 5 deletions(-)
diff -puN arch/x86/kernel/smpboot.c~x86-reduce-clock-calibration-time-during-slave-cpu-startup arch/x86/kernel/smpboot.c
--- a/arch/x86/kernel/smpboot.c~x86-reduce-clock-calibration-time-during-slave-cpu-startup
+++ a/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 -puN arch/x86/kernel/tsc.c~x86-reduce-clock-calibration-time-during-slave-cpu-startup arch/x86/kernel/tsc.c
--- a/arch/x86/kernel/tsc.c~x86-reduce-clock-calibration-time-during-slave-cpu-startup
+++ a/arch/x86/kernel/tsc.c
@@ -995,3 +995,22 @@ void __init tsc_init(void)
check_system_tsc_reliable();
}
+/*
+ * 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;
+}
+
diff -puN init/calibrate.c~x86-reduce-clock-calibration-time-during-slave-cpu-startup init/calibrate.c
--- a/init/calibrate.c~x86-reduce-clock-calibration-time-during-slave-cpu-startup
+++ a/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 "
_
Subject: Subject: x86: reduce clock calibration time during slave cpu startup
Patches currently in -mm which might be from steiner@xxxxxxx are
linux-next.patch
x86-reduce-clock-calibration-time-during-slave-cpu-startup.patch
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