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Subject[PATCH 1/2] x86: Add cmdline "cpu_init_udelay=N" to specify cpu_up() delay
Date
From: Len Brown <len.brown@intel.com>

No change to default behavior.

Replace the hard-coded mdelay(10) in cpu_up() with a variable udelay,
that is set to a defined default -- rather than a magic number.

Add a boot-time override, "cpu_init_udelay=N"

Signed-off-by: Len Brown <len.brown@intel.com>
---
Documentation/kernel-parameters.txt | 6 ++++++
arch/x86/kernel/smpboot.c | 23 ++++++++++++++++++++++-
arch/x86/kernel/smpboot.c.rej | 11 +++++++++++
3 files changed, 39 insertions(+), 1 deletion(-)
create mode 100644 arch/x86/kernel/smpboot.c.rej

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 61ab162..a320a41 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -746,6 +746,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
cpuidle.off=1 [CPU_IDLE]
disable the cpuidle sub-system

+ cpu_init_udelay=N
+ [X86] Delay for N microsec between assert and de-assert
+ of APIC INIT to start processors. This delay occurs
+ on every CPU online, such as boot, and resume from suspend.
+ Default: 10000
+
cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
Format:
<first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 51203f6..0629a8e 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -514,6 +514,27 @@ void __inquire_remote_apic(int apicid)
}

/*
+ * The Multiprocessor Specification 1.4 (1997) example code suggests
+ * that there should be a 10ms delay between the BSP asserting INIT
+ * and de-asserting INIT, when starting a remote processor.
+ * But that slows boot and resume on modern processors, which include
+ * many cores and don't require that delay.
+ *
+ * Cmdline "init_cpu_udelay=" is available to over-ride this delay.
+ */
+#define UDELAY_10MS_DEFAULT 10000
+
+static unsigned int init_udelay = UDELAY_10MS_DEFAULT;
+
+static int __init cpu_init_udelay(char *str)
+{
+ get_option(&str, &init_udelay);
+
+ return 0;
+}
+early_param("cpu_init_udelay", cpu_init_udelay);
+
+/*
* Poke the other CPU in the eye via NMI to wake it up. Remember that the normal
* INIT, INIT, STARTUP sequence will reset the chip hard for us, and this
* won't ... remember to clear down the APIC, etc later.
@@ -584,7 +605,7 @@ wakeup_secondary_cpu_via_init(int phys_apicid, unsigned long start_eip)
pr_debug("Waiting for send to finish...\n");
send_status = safe_apic_wait_icr_idle();

- mdelay(10);
+ mdelay(init_udelay);

pr_debug("Deasserting INIT\n");

diff --git a/arch/x86/kernel/smpboot.c.rej b/arch/x86/kernel/smpboot.c.rej
new file mode 100644
index 0000000..ccf0bd0
--- /dev/null
+++ b/arch/x86/kernel/smpboot.c.rej
@@ -0,0 +1,11 @@
+--- arch/x86/kernel/smpboot.c
++++ arch/x86/kernel/smpboot.c
+@@ -607,7 +628,7 @@ wakeup_secondary_cpu_via_init(int phys_apicid, unsigned long start_eip)
+ pr_debug("Waiting for send to finish...\n");
+ send_status = safe_apic_wait_icr_idle();
+
+- mdelay(10);
++ udelay(init_udelay);
+
+ pr_debug("Deasserting INIT\n");
+
--
2.4.0.rc1



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