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Date: Tue, 09 Sep 2014 23:05:33 +0200
From: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
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Subject: Re: [Xenomai] real-time guarantee issues on xenomai 2.6.2.1
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To: Paul Janzen <pcj@xenomai.sez.to>
Cc: xenomai@xenomai.org

On 08/11/2014 07:43 PM, Paul Janzen wrote:
> Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org> writes:
> 
>> What about combining the 2, like:
>>
>> 	} else {
>> 		xnarch_memory_barrier();
>> 		cpu_relax();
>> 	}
> 
> No, this does not help either.


Could you try the following patch?

diff --git a/include/asm-generic/bits/pod.h b/include/asm-generic/bits/pod.h
index a6be0dc..cfb0c71 100644
--- a/include/asm-generic/bits/pod.h
+++ b/include/asm-generic/bits/pod.h
@@ -248,6 +248,7 @@ void __xnlock_spin(xnlock_t *lock /*, */ XNLOCK_DBG_CONTEXT_ARGS)
 			cpu_relax();
 			xnlock_dbg_spinning(lock, cpu, &spin_limit /*, */
 					    XNLOCK_DBG_PASS_CONTEXT);
+			xnarch_memory_barrier();
 		} while(atomic_read(&lock->owner) != ~0);
 }
 EXPORT_SYMBOL_GPL(__xnlock_spin);
diff --git a/include/asm-generic/system.h b/include/asm-generic/system.h
index 25bd83f..7a8c4d0 100644
--- a/include/asm-generic/system.h
+++ b/include/asm-generic/system.h
@@ -378,6 +378,8 @@ static inline void xnlock_put(xnlock_t *lock)
 	xnarch_memory_barrier();
 
 	atomic_set(&lock->owner, ~0);
+
+	xnarch_memory_barrier();
 }
 
 static inline spl_t
diff --git a/ksrc/nucleus/vfile.c b/ksrc/nucleus/vfile.c
index c8e0363..066c12f 100644
--- a/ksrc/nucleus/vfile.c
+++ b/ksrc/nucleus/vfile.c
@@ -279,6 +279,15 @@ redo:
 			data += vfile->datasz;
 			it->nrdata++;
 		}
+#ifdef CONFIG_SMP
+		{
+			/* Leave some time for other cpus to get the lock */
+			xnticks_t wakeup = xnarch_get_cpu_tsc();
+			wakeup += xnarch_ns_to_tsc(1000);
+			while ((xnsticks_t)(xnarch_get_cpu_tsc() - wakeup) < 0)
+				cpu_relax();
+		}
+#endif
 	}
 
 	if (ret < 0) {


-- 
                                                                Gilles.