From d68921f9bd148359e6d01c84aaa2e32bfbd82970 Mon Sep 17 00:00:00 2001 From: Len Brown Date: Mon, 11 May 2015 17:27:09 -0400 Subject: [PATCH] x86/smp/boot: Add cmdline "cpu_init_udelay=N" to specify cpu_up() delay MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Cc: Alan Cox Cc: Arjan van de Ven Cc: Borislav Petkov Cc: H. Peter Anvin Cc: Jan H. Schönherr Cc: Linus Torvalds Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/2fe8e6c798e8def271122f62df9bbf58dc283e2a.1431379433.git.len.brown@intel.com Signed-off-by: Ingo Molnar --- Documentation/kernel-parameters.txt | 6 ++++++ arch/x86/kernel/smpboot.c | 23 ++++++++++++++++++++++- 2 files changed, 28 insertions(+), 1 deletion(-) 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: ,,,[,] 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"); -- 2.7.4