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Subject[PATCH 2/2] x86: speed cpu_up by quirking cpu_init_udelay
Date
From: Len Brown <len.brown@intel.com>

Modern processor familes are on a white-list to remove
the costly cpu_init_udelay 10000. Unknown processor families
get the traditional 10ms delay in cpu_up().

This seemed more efficient than forcing modern processors
to exhaustively search a black-list having all the old
processor families that should have a 10ms delay.
For not only are new processor familes infrequently added,
the white list also allows a delay other than 0, if needed.

Signed-off-by: Len Brown <len.brown@intel.com>
---
arch/x86/kernel/smpboot.c | 37 +++++++++++++++++++++++++++++++++++--
1 file changed, 35 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 76734f4..34a08ff 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -76,6 +76,7 @@
#include <asm/i8259.h>
#include <asm/realmode.h>
#include <asm/misc.h>
+#include <asm/cpu_device_id.h>

/* State of each CPU */
DEFINE_PER_CPU(int, cpu_state) = { 0 };
@@ -521,14 +522,44 @@ void __inquire_remote_apic(int apicid)
* 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.
- *
+ * many cores and don't require that delay. Here we default to the
+ * legacy delay, but quirk new processors to skip the delay.
* cmdline "init_cpu_udelay=" is available to specify this delay.
*/
#define UDELAY_10MS_DEFAULT 10000

static unsigned int init_udelay = UDELAY_10MS_DEFAULT;

+static const struct x86_cpu_id init_udelay_ids[] = {
+ { X86_VENDOR_INTEL, 0x6, X86_MODEL_ANY, X86_FEATURE_ANY, 0 },
+ { X86_VENDOR_AMD, 0x16, X86_MODEL_ANY, X86_FEATURE_ANY, 0 },
+ { X86_VENDOR_AMD, 0x15, X86_MODEL_ANY, X86_FEATURE_ANY, 0 },
+ { X86_VENDOR_AMD, 0x14, X86_MODEL_ANY, X86_FEATURE_ANY, 0 },
+ { X86_VENDOR_AMD, 0x12, X86_MODEL_ANY, X86_FEATURE_ANY, 0 },
+ { X86_VENDOR_AMD, 0x11, X86_MODEL_ANY, X86_FEATURE_ANY, 0 },
+ { X86_VENDOR_AMD, 0x10, X86_MODEL_ANY, X86_FEATURE_ANY, 0 },
+ { X86_VENDOR_AMD, 0xF, X86_MODEL_ANY, X86_FEATURE_ANY, 0 },
+ {}
+};
+MODULE_DEVICE_TABLE(x86cpu, init_udelay_ids);
+
+static void __init smp_quirk_init_udelay(void)
+{
+ const struct x86_cpu_id *id;
+ unsigned int new_udelay;
+
+ id = x86_match_cpu(init_udelay_ids);
+ if (id == NULL)
+ return; /* if no match, keep default */
+
+ if (init_udelay != UDELAY_10MS_DEFAULT)
+ return; /* if cmdline changed from default, leave it alone */
+
+ new_udelay = (unsigned long) id->driver_data;
+ pr_debug("cpu_init_udelay quirk to %d, was %d", new_udelay, init_udelay);
+ init_udelay = new_udelay;
+}
+
static int __init cpu_init_udelay(char *str)
{
unsigned int new_udelay;
@@ -1196,6 +1227,8 @@ 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)
--
2.4.0.rc1


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