Message-ID: <20131120175233.GB2582@e103592.cambridge.arm.com>
Date:	Wed, 20 Nov 2013 17:52:33 +0000
From:	Dave Martin <Dave.Martin@....com>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:	rostedt@...dmis.org, linaro-kernel@...ts.linaro.org,
	shaojie.sun@...aro.org, patches@...aro.org, fweisbec@...il.com,
	broonie@...aro.org, linux-kernel@...r.kernel.org, mingo@...hat.com,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH V3] ARM: trace: Add tracepoint for the Inter Processor
 Interrupt

On Tue, Nov 19, 2013 at 03:09:18PM +0100, Daniel Lezcano wrote:
> On 11/07/2013 10:01 AM, Daniel Lezcano wrote:
> >The Inter Processor Interrupt is used on ARM to tell another processor to do
> >a specific action. This is mainly used to emulate a timer interrupt on an idle
> >cpu, force a cpu to reschedule or run a function on another processor context.
> >
> >Add a tracepoint when raising an IPI and in the entry/exit handler functions.
> >
> >When a cpu raises an IPI, the targeted cpus is an interesting information, the
> >cpumask conversion in hexa is added in the trace using the cpumask_scnprintf
> >function.
> >
> >Tested-on Vexpress TC2 (5 processors).
> >Tested-on u8500 (2 processors).
> >
> >Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> 
> Hi guys,
> 
> did you have time to look at this patch ?

I just spotted this recently.

It seems a potentially useful idea, and seems to work (on ARM Vexpress/
TC2 anyway, which is what I have in front of me right now).

> We are writing a tool [1] to do some statistics about the cpu's idle
> times and giving the source of the wakeup. We hope it could be
> useful for the community to do some measurements but we need the IPI
> tracepoints to be more accurate.

It's not obvious to me what already exists.  Are the new tracepoints
giving genuinely more information?  Or otherwise, how/why is the
information "more accurate" than what was available previously?

> 
> Thanks in advance
>   -- Daniel
> 
> [1] https://git.linaro.org/gitweb?p=tools/idlestat.git;a=summary
> 
> >---
> >  arch/arm/include/asm/smp.h   |    9 ++++
> >  arch/arm/kernel/smp.c        |   34 +++++++------
> >  arch/arm64/include/asm/smp.h |    7 +++
> >  arch/arm64/kernel/smp.c      |   21 ++++++--

Is there any reason for this to be specific to ARM?

Not all arches have that ipi_msg_type enum, so it would be worth
thinking about what is common and how to make it more generic.

Wiring up the tracepoint for other arches could be left to other
people, but it's a good idea to have a framework that they can
fit into.

> >  include/trace/events/ipi.h   |  112 ++++++++++++++++++++++++++++++++++++++++++
> >  5 files changed, 164 insertions(+), 19 deletions(-)
> >  create mode 100644 include/trace/events/ipi.h
> >
> >diff --git a/arch/arm/include/asm/smp.h b/arch/arm/include/asm/smp.h
> >index a8cae71c..788706c 100644
> >--- a/arch/arm/include/asm/smp.h
> >+++ b/arch/arm/include/asm/smp.h
> >@@ -18,6 +18,15 @@
> >  # error "<asm/smp.h> included in non-SMP build"
> >  #endif
> >
> >+enum ipi_msg_type {
> >+	IPI_WAKEUP,
> >+	IPI_TIMER,
> >+	IPI_RESCHEDULE,
> >+	IPI_CALL_FUNC,
> >+	IPI_CALL_FUNC_SINGLE,
> >+	IPI_CPU_STOP,
> >+};
> >+
> >  #define raw_smp_processor_id() (current_thread_info()->cpu)
> >
> >  struct seq_file;
> >diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
> >index 72024ea..9ca8ce8 100644
> >--- a/arch/arm/kernel/smp.c
> >+++ b/arch/arm/kernel/smp.c
> >@@ -46,6 +46,9 @@
> >  #include <asm/mach/arch.h>
> >  #include <asm/mpu.h>
> >
> >+#define CREATE_TRACE_POINTS
> >+#include <trace/events/ipi.h>
> >+
> >  /*
> >   * as from 2.5, kernels no longer have an init_tasks structure
> >   * so we need some other way of telling a new secondary core
> >@@ -59,15 +62,6 @@ struct secondary_data secondary_data;
> >   */
> >  volatile int pen_release = -1;
> >
> >-enum ipi_msg_type {
> >-	IPI_WAKEUP,
> >-	IPI_TIMER,
> >-	IPI_RESCHEDULE,
> >-	IPI_CALL_FUNC,
> >-	IPI_CALL_FUNC_SINGLE,
> >-	IPI_CPU_STOP,

There are a couple of new entries you'll need to add when rebasing.
They'll also need adding in show_ipi_name().

> >-};
> >-
> >  static DECLARE_COMPLETION(cpu_running);
> >
> >  static struct smp_operations smp_ops;
> >@@ -433,19 +427,25 @@ void __init set_smp_cross_call(void (*fn)(const struct cpumask *, unsigned int))
> >  		smp_cross_call = fn;
> >  }
> >
> >+static void ipi_raise(const struct cpumask *mask, int ipinr)
> >+{
> >+	trace_ipi_raise(mask, ipinr);
> >+	smp_cross_call(mask, ipinr);
> >+}
> >+
> >  void arch_send_call_function_ipi_mask(const struct cpumask *mask)
> >  {
> >-	smp_cross_call(mask, IPI_CALL_FUNC);
> >+	ipi_raise(mask, IPI_CALL_FUNC);
> >  }
> >
> >  void arch_send_wakeup_ipi_mask(const struct cpumask *mask)
> >  {
> >-	smp_cross_call(mask, IPI_WAKEUP);
> >+	ipi_raise(mask, IPI_WAKEUP);
> >  }
> >
> >  void arch_send_call_function_single_ipi(int cpu)
> >  {
> >-	smp_cross_call(cpumask_of(cpu), IPI_CALL_FUNC_SINGLE);
> >+	ipi_raise(cpumask_of(cpu), IPI_CALL_FUNC_SINGLE);
> >  }
> >
> >  static const char *ipi_types[NR_IPI] = {
> >@@ -487,7 +487,7 @@ u64 smp_irq_stat_cpu(unsigned int cpu)
> >  #ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST
> >  void tick_broadcast(const struct cpumask *mask)
> >  {
> >-	smp_cross_call(mask, IPI_TIMER);
> >+	ipi_raise(mask, IPI_TIMER);
> >  }
> >  #endif
> >
> >@@ -528,6 +528,8 @@ void handle_IPI(int ipinr, struct pt_regs *regs)
> >  	unsigned int cpu = smp_processor_id();
> >  	struct pt_regs *old_regs = set_irq_regs(regs);
> >
> >+	trace_ipi_handler_entry(ipinr);
> >+
> >  	if (ipinr < NR_IPI)
> >  		__inc_irq_stat(cpu, ipi_irqs[ipinr]);
> >
> >@@ -571,11 +573,13 @@ void handle_IPI(int ipinr, struct pt_regs *regs)
> >  		break;
> >  	}
> >  	set_irq_regs(old_regs);
> >+
> >+	trace_ipi_handler_exit(ipinr);
> >  }
> >
> >  void smp_send_reschedule(int cpu)
> >  {
> >-	smp_cross_call(cpumask_of(cpu), IPI_RESCHEDULE);
> >+	ipi_raise(cpumask_of(cpu), IPI_RESCHEDULE);
> >  }
> >
> >  void smp_send_stop(void)
> >@@ -586,7 +590,7 @@ void smp_send_stop(void)
> >  	cpumask_copy(&mask, cpu_online_mask);
> >  	cpumask_clear_cpu(smp_processor_id(), &mask);
> >  	if (!cpumask_empty(&mask))
> >-		smp_cross_call(&mask, IPI_CPU_STOP);
> >+		ipi_raise(&mask, IPI_CPU_STOP);
> >
> >  	/* Wait up to one second for other CPUs to stop */
> >  	timeout = USEC_PER_SEC;
> >diff --git a/arch/arm64/include/asm/smp.h b/arch/arm64/include/asm/smp.h
> >index 4b8023c..7ebaa3a 100644
> >--- a/arch/arm64/include/asm/smp.h
> >+++ b/arch/arm64/include/asm/smp.h
> >@@ -24,6 +24,13 @@
> >  # error "<asm/smp.h> included in non-SMP build"
> >  #endif
> >
> >+enum ipi_msg_type {
> >+	IPI_RESCHEDULE,
> >+	IPI_CALL_FUNC,
> >+	IPI_CALL_FUNC_SINGLE,
> >+	IPI_CPU_STOP,
> >+};
> >+
> >  #define raw_smp_processor_id() (current_thread_info()->cpu)
> >
> >  struct seq_file;
> >diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> >index 78db90d..c987b9f 100644
> >--- a/arch/arm64/kernel/smp.c
> >+++ b/arch/arm64/kernel/smp.c
> >@@ -48,6 +48,9 @@
> >  #include <asm/tlbflush.h>
> >  #include <asm/ptrace.h>
> >
> >+#define CREATE_TRACE_POINTS
> >+#include <trace/events/ipi.h>
> >+
> >  /*
> >   * as from 2.5, kernels no longer have an init_tasks structure
> >   * so we need some other way of telling a new secondary core
> >@@ -426,14 +429,20 @@ void __init set_smp_cross_call(void (*fn)(const struct cpumask *, unsigned int))
> >  	smp_cross_call = fn;
> >  }
> >
> >+static void ipi_raise(const struct cpumask *mask, int ipinr)
> >+{
> >+	trace_ipi_raise(mask, ipinr);
> >+	smp_cross_call(mask, ipinr);
> >+}
> >+
> >  void arch_send_call_function_ipi_mask(const struct cpumask *mask)
> >  {
> >-	smp_cross_call(mask, IPI_CALL_FUNC);
> >+	ipi_raise(mask, IPI_CALL_FUNC);
> >  }
> >
> >  void arch_send_call_function_single_ipi(int cpu)
> >  {
> >-	smp_cross_call(cpumask_of(cpu), IPI_CALL_FUNC_SINGLE);
> >+	ipi_raise(cpumask_of(cpu), IPI_CALL_FUNC_SINGLE);
> >  }
> >
> >  static const char *ipi_types[NR_IPI] = {
> >@@ -501,6 +510,8 @@ void handle_IPI(int ipinr, struct pt_regs *regs)
> >  	unsigned int cpu = smp_processor_id();
> >  	struct pt_regs *old_regs = set_irq_regs(regs);
> >
> >+	trace_ipi_handler_entry(ipinr);
> >+
> >  	if (ipinr >= IPI_RESCHEDULE && ipinr < IPI_RESCHEDULE + NR_IPI)
> >  		__inc_irq_stat(cpu, ipi_irqs[ipinr - IPI_RESCHEDULE]);
> >
> >@@ -532,11 +543,13 @@ void handle_IPI(int ipinr, struct pt_regs *regs)
> >  		break;
> >  	}
> >  	set_irq_regs(old_regs);
> >+
> >+	trace_ipi_handler_exit(ipinr);
> >  }
> >
> >  void smp_send_reschedule(int cpu)
> >  {
> >-	smp_cross_call(cpumask_of(cpu), IPI_RESCHEDULE);
> >+	ipi_raise(cpumask_of(cpu), IPI_RESCHEDULE);
> >  }
> >
> >  void smp_send_stop(void)
> >@@ -549,7 +562,7 @@ void smp_send_stop(void)
> >  		cpumask_copy(&mask, cpu_online_mask);
> >  		cpu_clear(smp_processor_id(), mask);
> >
> >-		smp_cross_call(&mask, IPI_CPU_STOP);
> >+		ipi_raise(&mask, IPI_CPU_STOP);
> >  	}
> >
> >  	/* Wait up to one second for other CPUs to stop */
> >diff --git a/include/trace/events/ipi.h b/include/trace/events/ipi.h
> >new file mode 100644
> >index 0000000..fa22d4f
> >--- /dev/null
> >+++ b/include/trace/events/ipi.h
> >@@ -0,0 +1,112 @@
> >+#undef TRACE_SYSTEM
> >+#define TRACE_SYSTEM ipi

Would it make sense to put these under irq instead?

IPIs are a special kind of interrupt, but interrupts nonetheless.

irq:ipi_ might make sense as a prefix ... the IRQ folks might have a
view though.

> >+
> >+#if !defined(_TRACE_IPI_H) || defined(TRACE_HEADER_MULTI_READ)
> >+#define _TRACE_IPI_H
> >+
> >+#include <linux/tracepoint.h>
> >+
> >+#define ipi_name(ipinr) { IPI_##ipinr, #ipinr }
> >+#define show_ipi_name(val)				\
> >+	__print_symbolic(val,				\
> >+			 ipi_name(WAKEUP),		\
> >+			 ipi_name(TIMER),		\
> >+			 ipi_name(RESCHEDULE),		\
> >+			 ipi_name(CALL_FUNC),		\
> >+			 ipi_name(CALL_FUNC_SINGLE),	\
> >+			 ipi_name(CPU_STOP))

I can see this being a bit of a pain to maintain.  How do we keep it in
sync with the arch headers?

One option would be for the arch to provide this, or find a way to
define the common entries in one place and the arch-specific entries
via the arch headers.

Cheers
---Dave

> >+
> >+#define show_cpumask(srcp)				\
> >+	({						\
> >+		char *buf = __get_dynamic_array(buf);	\
> >+		cpumask_scnprintf(buf, NR_CPUS, srcp);	\
> >+		buf;					\
> >+	})
> >+
> >+DECLARE_EVENT_CLASS(ipi,
> >+
> >+    TP_PROTO(int ipinr),
> >+
> >+    TP_ARGS(ipinr),
> >+
> >+    TP_STRUCT__entry(
> >+	    __field(int, ipinr)
> >+    ),
> >+
> >+    TP_fast_assign(
> >+	    __entry->ipinr = ipinr;
> >+    ),
> >+
> >+    TP_printk("ipi=%d, name=%s", __entry->ipinr,
> >+	      show_ipi_name(__entry->ipinr))
> >+);
> >+
> >+/**
> >+ * ipi_handle_entry - called right before the IPI handler
> >+ * @ipinr: the IPI number
> >+ *
> >+ * The @ipinr value must be valid and the action name associated with
> >+ * the IPI value is given in the trace.
> >+ */
> >+DEFINE_EVENT_CONDITION(ipi, ipi_handler_entry,
> >+
> >+    TP_PROTO(int ipinr),
> >+
> >+    TP_ARGS(ipinr),
> >+
> >+    TP_CONDITION(ipinr < NR_IPI && ipinr >= 0)
> >+);
> >+
> >+/**
> >+ * ipi_handle_exit - called right after the IPI handler
> >+ * @ipinr: the IPI number
> >+ *
> >+ * The @ipinr value must be valid and the action name associated with
> >+ * the IPI value is given in the trace.
> >+ */
> >+DEFINE_EVENT_CONDITION(ipi, ipi_handler_exit,
> >+
> >+    TP_PROTO(int ipinr),
> >+
> >+    TP_ARGS(ipinr),
> >+
> >+    TP_CONDITION(ipinr < NR_IPI && ipinr >= 0)
> >+);
> >+
> >+/**
> >+ * ipi_raise - called when a smp cross call is made
> >+ * @ipinr: the IPI number
> >+ * @cpumask: the recipients for the IPI
> >+ *
> >+ * The @ipinr value must be valid and the action name associated with
> >+ * the IPI value is given in the trace as well as the cpumask of the
> >+ * targeted cpus.
> >+ */
> >+TRACE_EVENT_CONDITION(ipi_raise,
> >+
> >+    TP_PROTO(const struct cpumask *cpumask, int ipinr),
> >+
> >+    TP_ARGS(cpumask, ipinr),
> >+
> >+    TP_CONDITION(ipinr < NR_IPI && ipinr >= 0),
> >+
> >+    TP_STRUCT__entry(
> >+	    __field(int, ipinr)
> >+	    __field(const struct cpumask *, cpumask)
> >+	    __dynamic_array(char, buf, NR_CPUS)
> >+    ),
> >+
> >+    TP_fast_assign(
> >+	    __entry->ipinr = ipinr;
> >+	    __entry->cpumask = cpumask;
> >+    ),
> >+
> >+    TP_printk("ipi=%d, cpumask=0x%s, name=%s", __entry->ipinr,
> >+	      show_cpumask(__entry->cpumask),
> >+	      show_ipi_name(__entry->ipinr))
> >+);
> >+
> >+#endif /* _TRACE_IPI_H */
> >+
> >+/* This part must be outside protection */
> >+#include <trace/define_trace.h>
> >
> 
> 
> -- 
>  <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs
> 
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> 
> 
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