[patch] x86, apic: use tsc deadline for oneshot when available
From: Suresh Siddha
Date: Mon Oct 22 2012 - 17:35:57 EST
Thomas, You wanted to run some tests with this, right? Please give it a
try and see if this is ok to be pushed to the -tip.
thanks,
suresh
--8<--
From: Suresh Siddha <suresh.b.siddha@xxxxxxxxx>
Subject: x86, apic: use tsc deadline for oneshot when available
If the TSC deadline mode is supported, LAPIC timer one-shot mode can be
implemented using IA32_TSC_DEADLINE MSR. An interrupt will be generated
when the TSC value equals or exceeds the value in the IA32_TSC_DEADLINE
MSR.
This enables us to skip the APIC calibration during boot. Also,
in xapic mode, this enables us to skip the uncached apic access
to re-arm the APIC timer.
As this timer ticks at the high frequency TSC rate, we use the
TSC_DIVISOR (32) to work with the 32-bit restrictions in the clockevent
API's to avoid 64-bit divides etc (frequency is u32 and "unsigned long"
in the set_next_event(), max_delta limits the next event to 32-bit for
32-bit kernel).
Signed-off-by: Suresh Siddha <suresh.b.siddha@xxxxxxxxx>
---
Documentation/kernel-parameters.txt | 4 ++
arch/x86/include/asm/msr-index.h | 2 +
arch/x86/kernel/apic/apic.c | 66 ++++++++++++++++++++++++++---------
3 files changed, 55 insertions(+), 17 deletions(-)
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 9776f06..4aa9ca0 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1304,6 +1304,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
lapic [X86-32,APIC] Enable the local APIC even if BIOS
disabled it.
+ lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
+ value for LAPIC timer one-shot implementation. Default
+ back to the programmable timer unit in the LAPIC.
+
lapic_timer_c2_ok [X86,APIC] trust the local apic timer
in C2 power state.
diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 7f0edce..e400cdb 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -337,6 +337,8 @@
#define MSR_IA32_MISC_ENABLE_TURBO_DISABLE (1ULL << 38)
#define MSR_IA32_MISC_ENABLE_IP_PREF_DISABLE (1ULL << 39)
+#define MSR_IA32_TSC_DEADLINE 0x000006E0
+
/* P4/Xeon+ specific */
#define MSR_IA32_MCG_EAX 0x00000180
#define MSR_IA32_MCG_EBX 0x00000181
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index b17416e..b0c49b1 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -90,21 +90,6 @@ EXPORT_EARLY_PER_CPU_SYMBOL(x86_bios_cpu_apicid);
*/
DEFINE_EARLY_PER_CPU_READ_MOSTLY(int, x86_cpu_to_logical_apicid, BAD_APICID);
-/*
- * Knob to control our willingness to enable the local APIC.
- *
- * +1=force-enable
- */
-static int force_enable_local_apic __initdata;
-/*
- * APIC command line parameters
- */
-static int __init parse_lapic(char *arg)
-{
- force_enable_local_apic = 1;
- return 0;
-}
-early_param("lapic", parse_lapic);
/* Local APIC was disabled by the BIOS and enabled by the kernel */
static int enabled_via_apicbase;
@@ -133,6 +118,25 @@ static inline void imcr_apic_to_pic(void)
}
#endif
+/*
+ * Knob to control our willingness to enable the local APIC.
+ *
+ * +1=force-enable
+ */
+static int force_enable_local_apic __initdata;
+/*
+ * APIC command line parameters
+ */
+static int __init parse_lapic(char *arg)
+{
+ if (config_enabled(CONFIG_X86_32) && !arg)
+ force_enable_local_apic = 1;
+ else if (!strncmp(arg, "notscdeadline", 13))
+ setup_clear_cpu_cap(X86_FEATURE_TSC_DEADLINE_TIMER);
+ return 0;
+}
+early_param("lapic", parse_lapic);
+
#ifdef CONFIG_X86_64
static int apic_calibrate_pmtmr __initdata;
static __init int setup_apicpmtimer(char *s)
@@ -315,6 +319,7 @@ int lapic_get_maxlvt(void)
/* Clock divisor */
#define APIC_DIVISOR 16
+#define TSC_DIVISOR 32
/*
* This function sets up the local APIC timer, with a timeout of
@@ -333,6 +338,9 @@ static void __setup_APIC_LVTT(unsigned int clocks, int oneshot, int irqen)
lvtt_value = LOCAL_TIMER_VECTOR;
if (!oneshot)
lvtt_value |= APIC_LVT_TIMER_PERIODIC;
+ else if (boot_cpu_has(X86_FEATURE_TSC_DEADLINE_TIMER))
+ lvtt_value |= APIC_LVT_TIMER_TSCDEADLINE;
+
if (!lapic_is_integrated())
lvtt_value |= SET_APIC_TIMER_BASE(APIC_TIMER_BASE_DIV);
@@ -341,6 +349,11 @@ static void __setup_APIC_LVTT(unsigned int clocks, int oneshot, int irqen)
apic_write(APIC_LVTT, lvtt_value);
+ if (lvtt_value & APIC_LVT_TIMER_TSCDEADLINE) {
+ printk_once(KERN_DEBUG "TSC deadline timer enabled\n");
+ return;
+ }
+
/*
* Divide PICLK by 16
*/
@@ -453,6 +466,15 @@ static int lapic_next_event(unsigned long delta,
return 0;
}
+static int lapic_next_deadline(unsigned long delta,
+ struct clock_event_device *evt)
+{
+ u64 tsc;
+ rdtscll(tsc);
+ wrmsrl(MSR_IA32_TSC_DEADLINE, tsc + (((u64) delta) * TSC_DIVISOR));
+ return 0;
+}
+
/*
* Setup the lapic timer in periodic or oneshot mode
*/
@@ -533,7 +555,15 @@ static void __cpuinit setup_APIC_timer(void)
memcpy(levt, &lapic_clockevent, sizeof(*levt));
levt->cpumask = cpumask_of(smp_processor_id());
- clockevents_register_device(levt);
+ if (this_cpu_has(X86_FEATURE_TSC_DEADLINE_TIMER)) {
+ levt->features &= ~(CLOCK_EVT_FEAT_PERIODIC |
+ CLOCK_EVT_FEAT_DUMMY);
+ levt->set_next_event = lapic_next_deadline;
+ clockevents_config_and_register(levt,
+ (tsc_khz / TSC_DIVISOR) * 1000,
+ 0xF, ~0UL);
+ } else
+ clockevents_register_device(levt);
}
/*
@@ -661,7 +691,9 @@ static int __init calibrate_APIC_clock(void)
* in the clockevent structure and return.
*/
- if (lapic_timer_frequency) {
+ if (boot_cpu_has(X86_FEATURE_TSC_DEADLINE_TIMER)) {
+ return 0;
+ } else if (lapic_timer_frequency) {
apic_printk(APIC_VERBOSE, "lapic timer already calibrated %d\n",
lapic_timer_frequency);
lapic_clockevent.mult = div_sc(lapic_timer_frequency/APIC_DIVISOR,
--
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