Re: [PATCH 1/2] non-string based tsc unstable reasons

From: Daniel Walker
Date: Fri May 25 2007 - 17:34:03 EST

On Fri, 2007-05-25 at 23:05 +0200, Andi Kleen wrote:
> On Fri, May 25, 2007 at 12:32:10PM -0700, Daniel Walker wrote:
> > Just passing a string to mark_tsc_unstable() doesn't allow real code to change
> > based on the reason for the instablility. I changed mark_tsc_unstable()
> > to accept a string and a flag which denotes a general reason why the tsc
> > is unstable, and can be evaluated in code.
> >
>
> I still think that's the wrong way to do this. If there is any
> special action that should be done on particular unstable events
> it should call a separate function or an addon function.
> First putting it all together and then try to distingush it again
> doesn't seem nice.

Off list John indicated a different way of doing this, which is in the
patch below. This seems similar to what your describing above.. I'm fine
with this method although I think this is a little confusing cause
mark_tsc_sched_clock_unstable() also makes it unstable for gettimeofday.
Which isn't totally clear just by looking at the functions.. (It's also
a super long function name..)

Any comments?

-------

Subject: non-string based tsc unstable reasons

Just passing a string to mark_tsc_unstable() doesn't allow real code to change
based on the reason for the instablility. I changed mark_tsc_unstable()
to accept a string and a flag which denotes a general reason why the tsc
is unstable, and can be evaluated in code.

Signed-Off-By: Daniel Walker <dwalker@xxxxxxxxxx>

---

Against 2.6.22-rc2

arch/i386/kernel/cpu/cyrix.c | 10 ++++---
arch/i386/kernel/tsc.c | 36 +++++++++++++++-------------
arch/x86_64/kernel/time.c | 2 -
arch/x86_64/kernel/tsc.c | 26 ++++++++++++--------
arch/x86_64/kernel/tsc_sync.c | 2 -
drivers/acpi/processor_idle.c | 4 +--
include/asm-i386/mach-summit/mach_mpparse.h | 5 ++-
include/asm-i386/tsc.h | 21 +++++++++++++++-
include/asm-x86_64/timex.h | 1
9 files changed, 69 insertions(+), 38 deletions(-)

Index: linux-2.6.21/arch/i386/kernel/cpu/cyrix.c
===================================================================
--- linux-2.6.21.orig/arch/i386/kernel/cpu/cyrix.c
+++ linux-2.6.21/arch/i386/kernel/cpu/cyrix.c
@@ -274,12 +274,14 @@ static void __cpuinit init_cyrix(struct
vendor = read_pci_config_16(0, 0, 0x12, PCI_VENDOR_ID);
device = read_pci_config_16(0, 0, 0x12, PCI_DEVICE_ID);

- /*
- * The 5510/5520 companion chips have a funky PIT.
+ /*
+ * The 5510/5520 companion chips have a funky PIT
+ * and an unstable TSC.
*/
if (vendor == PCI_VENDOR_ID_CYRIX &&
- (device == PCI_DEVICE_ID_CYRIX_5510 || device == PCI_DEVICE_ID_CYRIX_5520))
- mark_tsc_unstable("cyrix 5510/5520 detected");
+ (device == PCI_DEVICE_ID_CYRIX_5510 ||
+ device == PCI_DEVICE_ID_CYRIX_5520))
+ mark_tsc_sched_clock_unstable("cyrix 5510/5520 detected");
}
#endif
c->x86_cache_size=16; /* Yep 16K integrated cache thats it */
Index: linux-2.6.21/arch/i386/kernel/tsc.c
===================================================================
--- linux-2.6.21.orig/arch/i386/kernel/tsc.c
+++ linux-2.6.21/arch/i386/kernel/tsc.c
@@ -56,6 +56,7 @@ __setup("notsc", tsc_setup);
* due to cpufreq or due to unsynced TSCs
*/
static int tsc_unstable;
+static int tsc_unstable_sched_clock;

static inline int check_tsc_unstable(void)
{
@@ -107,7 +108,7 @@ unsigned long long sched_clock(void)
/*
* Fall back to jiffies if there's no TSC available:
*/
- if (unlikely(!tsc_enabled))
+ if (unlikely(tsc_unstable_sched_clock))
/* No locking but a rare wrong value is not a big deal: */
return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);

@@ -230,7 +231,7 @@ time_cpufreq_notifier(struct notifier_bl
* TSC based sched_clock turns
* to junk w/ cpufreq
*/
- mark_tsc_unstable("cpufreq changes");
+ mark_tsc_gettimeofday_unstable("cpufreq changes");
}
}
}
@@ -275,26 +276,29 @@ static struct clocksource clocksource_ts
CLOCK_SOURCE_MUST_VERIFY,
};

-void mark_tsc_unstable(char *reason)
+void mark_tsc_unstable(enum tsc_unstable_flags flag, char *reason)
{
- if (!tsc_unstable) {
- tsc_unstable = 1;
- tsc_enabled = 0;
- printk("Marking TSC unstable due to: %s.\n", reason);
- /* Can be called before registration */
- if (clocksource_tsc.mult)
- clocksource_change_rating(&clocksource_tsc, 0);
- else
- clocksource_tsc.rating = 0;
+ switch (flag) {
+ case CLOCK_UNSTABLE_SCHED_CLOCK:
+ tsc_unstable_sched_clock = 1;
+ case CLOCK_UNSTABLE_GETTIMEOFDAY:
+ if (likely(tsc_unstable))
+ return;
+ tsc_unstable = 1;
+ tsc_enabled = 0;
+ printk("Marking TSC unstable due to: %s.\n", reason);
+ /* Can be called before registration */
+ if (clocksource_tsc.mult)
+ clocksource_change_rating(&clocksource_tsc, 0);
+ else
+ clocksource_tsc.rating = 0;
}
}
EXPORT_SYMBOL_GPL(mark_tsc_unstable);

static int __init dmi_mark_tsc_unstable(struct dmi_system_id *d)
{
- printk(KERN_NOTICE "%s detected: marking TSC unstable.\n",
- d->ident);
- tsc_unstable = 1;
+ mark_tsc_sched_clock_unstable((char*)d->ident);
return 0;
}

@@ -326,7 +330,7 @@ __cpuinit int unsynchronized_tsc(void)
if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) {
/* assume multi socket systems are not synchronized: */
if (num_possible_cpus() > 1)
- tsc_unstable = 1;
+ mark_tsc_gettimeofday_unstable("Non-Intel SMP system");
}
return tsc_unstable;
}
Index: linux-2.6.21/arch/x86_64/kernel/time.c
===================================================================
--- linux-2.6.21.orig/arch/x86_64/kernel/time.c
+++ linux-2.6.21/arch/x86_64/kernel/time.c
@@ -400,7 +400,7 @@ void __init time_init(void)
cpu_khz = tsc_calibrate_cpu_khz();

if (unsynchronized_tsc())
- mark_tsc_unstable("TSCs unsynchronized");
+ mark_tsc_gettimeofday_unstable("TSCs unsynchronized");

if (cpu_has(&boot_cpu_data, X86_FEATURE_RDTSCP))
vgetcpu_mode = VGETCPU_RDTSCP;
Index: linux-2.6.21/arch/x86_64/kernel/tsc.c
===================================================================
--- linux-2.6.21.orig/arch/x86_64/kernel/tsc.c
+++ linux-2.6.21/arch/x86_64/kernel/tsc.c
@@ -111,7 +111,7 @@ static int time_cpufreq_notifier(struct

tsc_khz = cpufreq_scale(tsc_khz_ref, ref_freq, freq->new);
if (!(freq->flags & CPUFREQ_CONST_LOOPS))
- mark_tsc_unstable("cpufreq changes");
+ mark_tsc_gettimeofday_unstable("cpufreq changes");
}

set_cyc2ns_scale(tsc_khz_ref);
@@ -199,16 +199,22 @@ static struct clocksource clocksource_ts
.vread = vread_tsc,
};

-void mark_tsc_unstable(char *reason)
+void mark_tsc_unstable(enum tsc_unstable_flags flag, char *reason)
{
- if (!tsc_unstable) {
- tsc_unstable = 1;
- printk("Marking TSC unstable due to %s\n", reason);
- /* Change only the rating, when not registered */
- if (clocksource_tsc.mult)
- clocksource_change_rating(&clocksource_tsc, 0);
- else
- clocksource_tsc.rating = 0;
+ if (likely(tsc_unstable))
+ return;
+
+ switch (flag) {
+ case CLOCK_UNSTABLE_SCHED_CLOCK:
+
+ case CLOCK_UNSTABLE_GETTIMEOFDAY:
+ tsc_unstable = 1;
+ printk("Marking TSC unstable due to: %s.\n", reason);
+ /* Can be called before registration */
+ if (clocksource_tsc.mult)
+ clocksource_change_rating(&clocksource_tsc, 0);
+ else
+ clocksource_tsc.rating = 0;
}
}
EXPORT_SYMBOL_GPL(mark_tsc_unstable);
Index: linux-2.6.21/arch/x86_64/kernel/tsc_sync.c
===================================================================
--- linux-2.6.21.orig/arch/x86_64/kernel/tsc_sync.c
+++ linux-2.6.21/arch/x86_64/kernel/tsc_sync.c
@@ -138,7 +138,7 @@ void __cpuinit check_tsc_sync_source(int
printk("\n");
printk(KERN_WARNING "Measured %Ld cycles TSC warp between CPUs,"
" turning off TSC clock.\n", max_warp);
- mark_tsc_unstable("check_tsc_sync_source failed");
+ mark_tsc_sched_clock_unstable("check_tsc_sync_source failed");
nr_warps = 0;
max_warp = 0;
last_tsc = 0;
Index: linux-2.6.21/drivers/acpi/processor_idle.c
===================================================================
--- linux-2.6.21.orig/drivers/acpi/processor_idle.c
+++ linux-2.6.21/drivers/acpi/processor_idle.c
@@ -475,7 +475,7 @@ static void acpi_processor_idle(void)

#ifdef CONFIG_GENERIC_TIME
/* TSC halts in C2, so notify users */
- mark_tsc_unstable("possible TSC halt in C2");
+ mark_tsc_sched_clock_unstable("possible TSC halt in C2");
#endif
/* Re-enable interrupts */
local_irq_enable();
@@ -517,7 +517,7 @@ static void acpi_processor_idle(void)

#ifdef CONFIG_GENERIC_TIME
/* TSC halts in C3, so notify users */
- mark_tsc_unstable("TSC halts in C3");
+ mark_tsc_sched_clock_unstable("TSC halts in C3");
#endif
/* Re-enable interrupts */
local_irq_enable();
Index: linux-2.6.21/include/asm-i386/mach-summit/mach_mpparse.h
===================================================================
--- linux-2.6.21.orig/include/asm-i386/mach-summit/mach_mpparse.h
+++ linux-2.6.21/include/asm-i386/mach-summit/mach_mpparse.h
@@ -30,7 +30,7 @@ static inline int mps_oem_check(struct m
(!strncmp(productid, "VIGIL SMP", 9)
|| !strncmp(productid, "EXA", 3)
|| !strncmp(productid, "RUTHLESS SMP", 12))){
- mark_tsc_unstable("Summit based system");
+ mark_tsc_gettimeofday_unstable("Summit based system");
use_cyclone = 1; /*enable cyclone-timer*/
setup_summit();
return 1;
@@ -44,7 +44,8 @@ static inline int acpi_madt_oem_check(ch
if (!strncmp(oem_id, "IBM", 3) &&
(!strncmp(oem_table_id, "SERVIGIL", 8)
|| !strncmp(oem_table_id, "EXA", 3))){
- mark_tsc_unstable("Summit based system");
+ mark_tsc_unstable(CLOCK_TSC_UNSYNCHRONIZED,
+ "Summit based system");
use_cyclone = 1; /*enable cyclone-timer*/
setup_summit();
return 1;
Index: linux-2.6.21/include/asm-i386/tsc.h
===================================================================
--- linux-2.6.21.orig/include/asm-i386/tsc.h
+++ linux-2.6.21/include/asm-i386/tsc.h
@@ -59,8 +59,27 @@ static __always_inline cycles_t get_cycl
return ret;
}

+/*
+ * These are the known reason why a TSC would be flaged
+ * as unstable.
+ */
+enum tsc_unstable_flags {
+ CLOCK_UNSTABLE_GETTIMEOFDAY = 0,
+ CLOCK_UNSTABLE_SCHED_CLOCK,
+};
+extern void mark_tsc_unstable(enum tsc_unstable_flags flag, char *reason);
+
+static inline void mark_tsc_gettimeofday_unstable(char *reason)
+{
+ mark_tsc_unstable(CLOCK_UNSTABLE_GETTIMEOFDAY, reason);
+}
+
+static inline void mark_tsc_sched_clock_unstable(char *reason)
+{
+ mark_tsc_unstable(CLOCK_UNSTABLE_SCHED_CLOCK, reason);
+}
+
extern void tsc_init(void);
-extern void mark_tsc_unstable(char *reason);
extern int unsynchronized_tsc(void);
extern void init_tsc_clocksource(void);

Index: linux-2.6.21/include/asm-x86_64/timex.h
===================================================================
--- linux-2.6.21.orig/include/asm-x86_64/timex.h
+++ linux-2.6.21/include/asm-x86_64/timex.h
@@ -27,6 +27,5 @@ extern int read_current_timer(unsigned l
#define NS_SCALE 10 /* 2^10, carefully chosen */
#define US_SCALE 32 /* 2^32, arbitralrily chosen */

-extern void mark_tsc_unstable(char *msg);
extern void set_cyc2ns_scale(unsigned long khz);
#endif


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