Re: [Xenomai-core] latencys drifting into negative (Xenomai 2.4.2/2.4.3)

[Jan Kiszka <jan.kiszka@domain.hid>]

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Sebastian Smolorz wrote:
> Jan Kiszka wrote:
>> Sebastian Smolorz wrote:
>>> Jan Kiszka wrote:
>>>> This patch may do the trick: it uses the inverted tsc-to-ns function 
>>>> instead of the frequency-based one. Be warned, it is totally 
>>>> untested inside Xenomai, I just ran it in a user space test program. 
>>>> But it may give an idea.
>>>
>>> Your patch needed two minor corrections (ns instead of ts in 
>>> functions xnarch_ns_to_tsc()) in order to compile. A short run (30 
>>> minutes) of latency -t1 seems to prove your bug-fix: There seems to 
>>> be no drift.
>>
>> That's good to hear.
>>
>>> If I got your patch correctly, it doesn't make xnarch_tsc_to_ns more 
>>> precise but introduces a new function xnarch_ns_to_tsc() which is 
>>> also less precise than the generic xnarch_ns_to_tsc(), right?
>>
>> Yes. It is now precisely the inverse imprecision, so to say. :)
>>
>>> So isn't there still the danger of getting wrong values when calling 
>>> xnarch_tsc_to_ns()  not in combination with xnarch_ns_to_tsc()?
>>
>> Only if the user decides to implement his own conversion. Xenomai with 
>> all its skins and both in kernel and user space should always run 
>> through the xnarch_* path.
> 
> OK, would you commit the patch?

Will do unless someone else has concerns. Gilles, Philippe? ARM and 
Blackfin then need to be fixed similarly, full patch attached.

Jan

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---
 ChangeLog                        |    7 +++++++
 include/asm-arm/bits/init.h      |    3 ++-
 include/asm-arm/bits/pod.h       |    7 +++++++
 include/asm-blackfin/bits/init.h |    3 ++-
 include/asm-blackfin/bits/pod.h  |    7 +++++++
 include/asm-x86/bits/init_32.h   |    3 ++-
 include/asm-x86/bits/init_64.h   |    3 ++-
 include/asm-x86/bits/pod_32.h    |    7 +++++++
 include/asm-x86/bits/pod_64.h    |    7 +++++++
 9 files changed, 43 insertions(+), 4 deletions(-)

Index: b/include/asm-x86/bits/init_32.h
===================================================================
--- a/include/asm-x86/bits/init_32.h
+++ b/include/asm-x86/bits/init_32.h
@@ -73,7 +73,7 @@ int xnarch_calibrate_sched(void)
 
 static inline int xnarch_init(void)
 {
-	extern unsigned xnarch_tsc_scale, xnarch_tsc_shift;
+	extern unsigned xnarch_tsc_scale, xnarch_tsc_shift, xnarch_tsc_divide;
 	int err;
 
 	err = rthal_init();
@@ -89,6 +89,7 @@ static inline int xnarch_init(void)
 
 	xnarch_init_llmulshft(1000000000, RTHAL_CPU_FREQ,
 			      &xnarch_tsc_scale, &xnarch_tsc_shift);
+	xnarch_tsc_divide = 1 << xnarch_tsc_shift;
 
 	err = xnarch_calibrate_sched();
 
Index: b/include/asm-x86/bits/init_64.h
===================================================================
--- a/include/asm-x86/bits/init_64.h
+++ b/include/asm-x86/bits/init_64.h
@@ -70,7 +70,7 @@ int xnarch_calibrate_sched(void)
 
 static inline int xnarch_init(void)
 {
-	extern unsigned xnarch_tsc_scale, xnarch_tsc_shift;
+	extern unsigned xnarch_tsc_scale, xnarch_tsc_shift, xnarch_tsc_divide;
 	int err;
 
 	err = rthal_init();
@@ -86,6 +86,7 @@ static inline int xnarch_init(void)
 
 	xnarch_init_llmulshft(1000000000, RTHAL_CPU_FREQ,
 			      &xnarch_tsc_scale, &xnarch_tsc_shift);
+	xnarch_tsc_divide = 1 << xnarch_tsc_shift;
 
 	err = xnarch_calibrate_sched();
 
Index: b/include/asm-x86/bits/pod_32.h
===================================================================
--- a/include/asm-x86/bits/pod_32.h
+++ b/include/asm-x86/bits/pod_32.h
@@ -25,6 +25,7 @@
 
 unsigned xnarch_tsc_scale;
 unsigned xnarch_tsc_shift;
+unsigned xnarch_tsc_divide;
 
 long long xnarch_tsc_to_ns(long long ts)
 {
@@ -32,6 +33,12 @@ long long xnarch_tsc_to_ns(long long ts)
 }
 #define XNARCH_TSC_TO_NS
 
+long long xnarch_ns_to_tsc(long long ns)
+{
+	return xnarch_llimd(ns, xnarch_tsc_divide, xnarch_tsc_scale);
+}
+#define XNARCH_NS_TO_TSC
+
 #include <asm-generic/xenomai/bits/pod.h>
 #include <asm/xenomai/switch.h>
 
Index: b/include/asm-x86/bits/pod_64.h
===================================================================
--- a/include/asm-x86/bits/pod_64.h
+++ b/include/asm-x86/bits/pod_64.h
@@ -24,6 +24,7 @@
 
 unsigned xnarch_tsc_scale;
 unsigned xnarch_tsc_shift;
+unsigned xnarch_tsc_divide;
 
 long long xnarch_tsc_to_ns(long long ts)
 {
@@ -31,6 +32,12 @@ long long xnarch_tsc_to_ns(long long ts)
 }
 #define XNARCH_TSC_TO_NS
 
+long long xnarch_ns_to_tsc(long long ns)
+{
+	return xnarch_llimd(ns, xnarch_tsc_divide, xnarch_tsc_scale);
+}
+#define XNARCH_NS_TO_TSC
+
 #include <asm-generic/xenomai/bits/pod.h>
 #include <asm/xenomai/switch.h>
 
Index: b/include/asm-arm/bits/init.h
===================================================================
--- a/include/asm-arm/bits/init.h
+++ b/include/asm-arm/bits/init.h
@@ -67,7 +67,7 @@ int xnarch_calibrate_sched(void)
 
 static inline int xnarch_init(void)
 {
-	extern unsigned xnarch_tsc_scale, xnarch_tsc_shift;
+	extern unsigned xnarch_tsc_scale, xnarch_tsc_shift, xnarch_tsc_divide;
 	int err;
 
 	err = rthal_init();
@@ -77,6 +77,7 @@ static inline int xnarch_init(void)
 
 	xnarch_init_llmulshft(1000000000, RTHAL_CPU_FREQ,
 			      &xnarch_tsc_scale, &xnarch_tsc_shift);
+	xnarch_tsc_divide = 1 << xnarch_tsc_shift;
 
 	err = xnarch_calibrate_sched();
 
Index: b/include/asm-arm/bits/pod.h
===================================================================
--- a/include/asm-arm/bits/pod.h
+++ b/include/asm-arm/bits/pod.h
@@ -25,6 +25,7 @@
 
 unsigned xnarch_tsc_scale;
 unsigned xnarch_tsc_shift;
+unsigned xnarch_tsc_divide;
 
 long long xnarch_tsc_to_ns(long long ts)
 {
@@ -32,6 +33,12 @@ long long xnarch_tsc_to_ns(long long ts)
 }
 #define XNARCH_TSC_TO_NS
 
+long long xnarch_ns_to_tsc(long long ns)
+{
+	return xnarch_llimd(ns, xnarch_tsc_divide, xnarch_tsc_scale);
+}
+#define XNARCH_NS_TO_TSC
+
 #include <asm-generic/xenomai/bits/pod.h>
 
 void xnpod_welcome_thread(struct xnthread *, int);
Index: b/include/asm-blackfin/bits/init.h
===================================================================
--- a/include/asm-blackfin/bits/init.h
+++ b/include/asm-blackfin/bits/init.h
@@ -66,7 +66,7 @@ int xnarch_calibrate_sched(void)
 
 static inline int xnarch_init(void)
 {
-	extern unsigned xnarch_tsc_scale, xnarch_tsc_shift;
+	extern unsigned xnarch_tsc_scale, xnarch_tsc_shift, xnarch_tsc_divide;
 	int err;
 
 	__ipipe_irq_tail_hook = (unsigned long)&xnpod_schedule_deferred;
@@ -84,6 +84,7 @@ static inline int xnarch_init(void)
 
 	xnarch_init_llmulshft(1000000000, RTHAL_CPU_FREQ,
 			      &xnarch_tsc_scale, &xnarch_tsc_shift);
+	xnarch_tsc_divide = 1 << xnarch_tsc_shift;
 
 	err = xnarch_calibrate_sched();
 
Index: b/include/asm-blackfin/bits/pod.h
===================================================================
--- a/include/asm-blackfin/bits/pod.h
+++ b/include/asm-blackfin/bits/pod.h
@@ -22,6 +22,7 @@
 
 unsigned xnarch_tsc_scale;
 unsigned xnarch_tsc_shift;
+unsigned xnarch_tsc_divide;
 
 long long xnarch_tsc_to_ns(long long ts)
 {
@@ -29,6 +30,12 @@ long long xnarch_tsc_to_ns(long long ts)
 }
 #define XNARCH_TSC_TO_NS
 
+long long xnarch_ns_to_tsc(long long ns)
+{
+	return xnarch_llimd(ns, xnarch_tsc_divide, xnarch_tsc_scale);
+}
+#define XNARCH_NS_TO_TSC
+
 #include <asm-generic/xenomai/bits/pod.h>
 
 void xnpod_welcome_thread(struct xnthread *, int);
Index: b/ChangeLog
===================================================================
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2008-04-04  Jan Kiszka  <jan.kiszka@domain.hid>
+
+	* include/asm-*/{pod.h,init.h}: Introduce arch-specific
+	xnarch_ns_to_tsc as inverse of mul-shift xnarch_tsc_to_ns instead
+	of converting back via CPU frequency. Avoids drifts between large
+	calculated versus measured dates.
+
 2008-04-02  Philippe Gerum  <rpm@xenomai.org>
 
 	* include/asm-generic/bits/mlock_alert.h:

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