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Subject[PATCH 1/1] x86: replace cpu_up hard-coded mdelay with variable
Date
From: Len Brown <len.brown@intel.com>

Default behavior unchanged.

cpu_up() has a hard-coded mdelay(10). Change that to a variable,
with default CONFIG_X86_INIT_MDELAY
and a boot-time override, "cpu_init_mdelay=N"

This patch adds mechanism without changing default policy.
Default policy will be changed in a subsequent patch.

Signed-off-by: Len Brown <len.brown@intel.com>
---
Documentation/kernel-parameters.txt | 7 +++++++
arch/x86/Kconfig | 15 +++++++++++++++
arch/x86/kernel/smpboot.c | 16 +++++++++++++++-
3 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index bfcb1a6..ec98968 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -737,6 +737,13 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
cpuidle.off=1 [CPU_IDLE]
disable the cpuidle sub-system

+ cpu_init_mdelay=N
+ [X86] Delay for N millisec between assert and de-assert
+ of APIC INIT to start processor. In most configurations,
+ this occurs once for every CPU upon boot, and online,
+ such as resume from suspend and resume from hibernate.
+ Default: 10
+
cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
Format:
<first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index b7d31ca..d2a91da 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -884,6 +884,21 @@ config SCHED_MC
making when dealing with multi-core CPU chips at a cost of slightly
increased overhead in some places. If unsure say N here.

+config X86_INIT_MDELAY
+ int "Milliseconds to wait to de-assert INIT upon CPU startup" if SMP
+ range 0 10
+ default "10"
+ ---help---
+ This allows you to specify how long the BSP will delay
+ between asserting INIT and de-asserting INIT when starting another CPU.
+ This delay is paid on each cpu-online operation, including boot-time,
+ resume from suspend, and resume from hibernate. The the value of
+ 10 millisec was specified by Multi-Processor Spec 1.4 in 1997.
+ But modern hardware does not require any delay.
+
+ The kernel boot-time parameter "cpu_init_mdelay="
+ will over-ride this build-time default.
+
source "kernel/Kconfig.preempt"

config UP_LATE_INIT
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index febc6aa..973621f 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -555,6 +555,20 @@ wakeup_secondary_cpu_via_nmi(int apicid, unsigned long start_eip)
return (send_status | accept_status);
}

+unsigned int x86_init_mdelay = CONFIG_X86_INIT_MDELAY;
+static int __init cpu_init_mdelay(char *str)
+{
+ unsigned int tmp;
+
+ get_option(&str, &tmp);
+ pr_info("x86_init_mdelay set to %d, was %d", tmp, x86_init_mdelay);
+ x86_init_mdelay = tmp;
+ return 0;
+}
+
+early_param("cpu_init_mdelay", cpu_init_mdelay);
+
+
static int
wakeup_secondary_cpu_via_init(int phys_apicid, unsigned long start_eip)
{
@@ -586,7 +600,7 @@ 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(x86_init_mdelay);

pr_debug("Deasserting INIT\n");

--
2.4.0.rc1


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