Re: [Xenomai] A possible mis-interaction between CONFIG_PREEMPT and GPIO IRQ handling for ARM, leading to extreme latency

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

On 05/22/2012 02:31 AM, Mitchell Tasman wrote:
> Hi.  I'm running an OMAP DM3725-based board with a 2.6.38.8 kernel, a 
> mid-May 2012 git snapshot of xenomai-2.6, and a backport (really just 
> application) of the patch that Gilles referenced in the "IRQ latency" 
> thread last week:
> 
> http://git.xenomai.org/?p=ipipe-gch.git;a=commit;h=81bfc05c4716b76e79f5e486baf4c52015a3b92c

Please try the following patch instead:

diff --git a/arch/arm/include/asm/ipipe.h b/arch/arm/include/asm/ipipe.h
index 9b17c06..a510b09 100644
--- a/arch/arm/include/asm/ipipe.h
+++ b/arch/arm/include/asm/ipipe.h
@@ -285,14 +285,15 @@ void __ipipe_grab_irq(int irq, struct pt_regs *regs);
 
 void __ipipe_exit_irq(struct pt_regs *regs);
 
-void __ipipe_handle_irq(int irq, struct pt_regs *regs);
+#define IPIPE_IRQF_NOACK    0x1
+#define IPIPE_IRQF_NOSYNC   0x2
+
+void __ipipe_handle_irq(int irq, int flags);
 
 static inline void ipipe_handle_chained_irq(unsigned int irq)
 {
-	struct pt_regs regs;    /* dummy */
-
 	ipipe_trace_irq_entry(irq);
-	__ipipe_handle_irq(irq, &regs);
+	__ipipe_handle_irq(irq, IPIPE_IRQF_NOSYNC);
 	ipipe_trace_irq_exit(irq);
 }
 
diff --git a/arch/arm/include/asm/smp_twd.h b/arch/arm/include/asm/smp_twd.h
index b49c8ac..f655b27 100644
--- a/arch/arm/include/asm/smp_twd.h
+++ b/arch/arm/include/asm/smp_twd.h
@@ -55,7 +55,7 @@ extern void __iomem *twd_base;
 #define __ipipe_mach_relay_ipi(ipi, thiscpu)	\
 	({					\
 		(void)(thiscpu);		\
-		__ipipe_handle_irq(ipi, NULL);	\
+		__ipipe_handle_irq(ipi, IPIPE_IRQF_NOACK);	\
 	})
 
 struct irq_desc;
diff --git a/arch/arm/kernel/ipipe.c b/arch/arm/kernel/ipipe.c
index f2f618c..ff93fa9 100644
--- a/arch/arm/kernel/ipipe.c
+++ b/arch/arm/kernel/ipipe.c
@@ -254,7 +254,7 @@ int ipipe_trigger_irq(unsigned irq)
 		return -EINVAL;
 #endif
 	local_irq_save_hw(flags);
-	__ipipe_handle_irq(irq, NULL);
+	__ipipe_handle_irq(irq, IPIPE_IRQF_NOACK);
 	local_irq_restore_hw(flags);
 
 	return 1;
@@ -462,7 +462,7 @@ out:
  * interrupt protection log is maintained here for each domain. Hw
  * interrupts are off on entry.
  */
-void __ipipe_handle_irq(int irq, struct pt_regs *regs)
+void __ipipe_handle_irq(int irq, int flags)
 {
 	struct ipipe_domain *this_domain, *next_domain;
 	struct list_head *head, *pos;
@@ -470,7 +470,7 @@ void __ipipe_handle_irq(int irq, struct pt_regs *regs)
 	int m_ack;
 
 	/* Software-triggered IRQs do not need any ack. */
-	m_ack = (regs == NULL);
+	m_ack = (flags & IPIPE_IRQF_NOACK) != 0;
 
 #ifdef CONFIG_IPIPE_DEBUG
 	if (unlikely(irq >= IPIPE_NR_IRQS) ||
@@ -490,7 +490,11 @@ void __ipipe_handle_irq(int irq, struct pt_regs *regs)
 				desc = ipipe_virtual_irq_p(irq) ? NULL : irq_to_desc(irq);
 				next_domain->irqs[irq].acknowledge(irq, desc);
 			}
-			__ipipe_dispatch_wired(next_domain, irq);
+			if ((flags & IPIPE_IRQF_NOSYNC) == 0)
+				__ipipe_dispatch_wired(next_domain, irq);
+			else
+				__ipipe_set_irq_pending(next_domain, irq);
+
 			return;
 		}
 	}
@@ -604,7 +608,7 @@ asmlinkage void __ipipe_grab_irq(int irq, struct pt_regs *regs)
 	ipipe_trace_begin(regs->ARM_ORIG_r0);
 #endif
 
-	__ipipe_handle_irq(irq, regs);
+	__ipipe_handle_irq(irq, 0);
 
 #ifdef CONFIG_IPIPE_TRACE_IRQSOFF
 	ipipe_trace_end(regs->ARM_ORIG_r0);
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 9ea207d..af02caa 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -527,7 +527,7 @@ __ipipe_grab_ipi(unsigned svc, struct pt_regs *regs) /* hw IRQs off */
 		__ipipe_do_vnmi(IPIPE_SERVICE_VNMI, NULL);
 	else if ((1 << svc) & IPI_IPIPE_ALL) {
 		virq = svc - IPI_IPIPE_CRITICAL + IPIPE_FIRST_IPI;
-		__ipipe_handle_irq(virq, NULL);
+		__ipipe_handle_irq(virq, IPIPE_IRQF_NOACK);
 	} else
 		__ipipe_mach_relay_ipi(svc, cpu);
 

-- 
                                                                Gilles.