linux-kernel - [tip:x86/apic] x86/smp/boot: Remove 10ms delay from cpu

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Message-ID: <tip-1a744cb356c57303fc97eb15a298032170f841fa@git.kernel.org>
Date:	Tue, 12 May 2015 00:39:53 -0700
From:	tip-bot for Len Brown <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	hpa@...or.com, mingo@...nel.org, linux-kernel@...r.kernel.org,
	jschoenh@...zon.de, arjan@...ux.intel.com, tglx@...utronix.de,
	len.brown@...el.com, torvalds@...ux-foundation.org,
	alan@...ux.intel.com, bp@...en8.de
Subject: [tip:x86/apic] x86/smp/boot: Remove 10ms delay from cpu_up()
  on modern processors

Commit-ID:  1a744cb356c57303fc97eb15a298032170f841fa
Gitweb:     http://git.kernel.org/tip/1a744cb356c57303fc97eb15a298032170f841fa
Author:     Len Brown <len.brown@...el.com>
AuthorDate: Mon, 11 May 2015 17:27:10 -0400
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 12 May 2015 08:54:33 +0200

x86/smp/boot: Remove 10ms delay from cpu_up() on modern processors

Modern processor familes do not require the 10ms delay
in cpu_up() to de-assert INIT.  This speeds up boot
and resume by 10ms per (application) processor.

Signed-off-by: Len Brown <len.brown@...el.com>
Cc: Alan Cox <alan@...ux.intel.com>
Cc: Arjan van de Ven <arjan@...ux.intel.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Jan H. Schönherr <jschoenh@...zon.de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/021ce30c88f216ad39686646421194dc25671e55.1431379433.git.len.brown@intel.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/smpboot.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 0629a8e..85bd6aa 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -521,6 +521,7 @@ void __inquire_remote_apic(int apicid)
  * many cores and don't require that delay.
  *
  * Cmdline "init_cpu_udelay=" is available to over-ride this delay.
+ * Modern processor families are quirked to remove the delay entirely.
  */
 #define UDELAY_10MS_DEFAULT 10000
 
@@ -534,6 +535,18 @@ static int __init cpu_init_udelay(char *str)
 }
 early_param("cpu_init_udelay", cpu_init_udelay);
 
+static void __init smp_quirk_init_udelay(void)
+{
+	/* if cmdline changed it from default, leave it alone */
+	if (init_udelay != UDELAY_10MS_DEFAULT)
+		return;
+
+	/* if modern processor, use no delay */
+	if (((boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) && (boot_cpu_data.x86 == 6)) ||
+	    ((boot_cpu_data.x86_vendor == X86_VENDOR_AMD) && (boot_cpu_data.x86 >= 0xF)))
+		init_udelay = 0;
+}
+
 /*
  * 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
@@ -1210,6 +1223,8 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
 		uv_system_init();
 
 	set_mtrr_aps_delayed_init();
+
+	smp_quirk_init_udelay();
 }
 
 void arch_enable_nonboot_cpus_begin(void)
--
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