[Xen-devel] [PATCH 10/15] xen: trace softirqs

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

Making it possible generate events showing the
activity and the behavior of the softirq subsystem.

Gate this with its specific Kconfig option (under
CONFIG_TRACING), and keep it in disabled state by
default.
---
Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Tim Deegan <tim@xxxxxxx>
---
 xen/Kconfig.debug          |    8 ++++++
 xen/common/softirq.c       |   58 ++++++++++++++++++++++++++++++++++++++++++++
 xen/include/public/trace.h |    7 +++++
 3 files changed, 73 insertions(+)

diff --git a/xen/Kconfig.debug b/xen/Kconfig.debug
index fd5cccc..4979e83 100644
--- a/xen/Kconfig.debug
+++ b/xen/Kconfig.debug
@@ -124,6 +124,14 @@ config TRACE_RCU
          Makes it possible generate events  showing the activity and the
          behavior of the RCU subsystem.
 
+config TRACE_SOFTIRQS
+       bool "Trace when softirqs are raised and handled" if EXPERT = "y"
+       default n
+       depends on TRACING
+       ---help---
+         Makes it possible to generate events related to raising and
+          handling of softirqs within Xen.
+
 config VERBOSE_DEBUG
        bool "Verbose debug messages"
        default DEBUG
diff --git a/xen/common/softirq.c b/xen/common/softirq.c
index 67c84ba..152788a 100644
--- a/xen/common/softirq.c
+++ b/xen/common/softirq.c
@@ -13,6 +13,7 @@
 #include <xen/mm.h>
 #include <xen/preempt.h>
 #include <xen/sched.h>
+#include <xen/trace.h>
 #include <xen/rcupdate.h>
 #include <xen/softirq.h>
 
@@ -25,6 +26,57 @@ static softirq_handler softirq_handlers[NR_SOFTIRQS];
 static DEFINE_PER_CPU(cpumask_t, batch_mask);
 static DEFINE_PER_CPU(unsigned int, batching);
 
+#ifdef CONFIG_TRACE_SOFTIRQS
+#define trace_raise(n)        TRACE_1D(TRC_XEN_SIRQ_RAISE, n)
+static inline void trace_raise_cpu(unsigned int nr, unsigned int cpu)
+{
+    struct {
+        uint16_t cpu, nr;
+    } d;
+
+    if ( likely(!tb_init_done) )
+        return;
+
+    d.nr = nr;
+    d.cpu = cpu;
+    __trace_var(TRC_XEN_SIRQ_RAISE_CPU, 1, sizeof(d), &d);
+}
+static inline
+void trace_raise_mask(unsigned int nr, const cpumask_t *m)
+{
+    struct {
+        uint32_t nr;
+        uint32_t mask[6];
+    } d;
+
+    if ( likely(!tb_init_done) )
+        return;
+
+    d.nr = nr;
+    memset(d.mask, 0, sizeof(d.mask));
+    memcpy(d.mask, m, min(sizeof(d.mask), sizeof(cpumask_t)));
+    __trace_var(TRC_XEN_SIRQ_RAISE_MASK, 1, sizeof(d), &d);
+}
+static inline void trace_handler(unsigned int nr, unsigned int cpu)
+{
+    struct {
+        uint16_t pending, nr;
+    } d;
+
+    if ( likely(!tb_init_done) )
+        return;
+
+    d.nr = nr;
+    d.pending = (uint16_t)softirq_pending(cpu);
+    __trace_var(TRC_XEN_SIRQ_HANDLER, 1, sizeof(d), &d);
+}
+#else /* !TRACE_SOFTIRQS */
+#define trace_raise(n)            do {} while ( 0 )
+#define trace_raise_cpu(n, c)     do {} while ( 0 )
+#define trace_raise_mask(n, m) do {} while ( 0 )
+#define trace_handler(n, c)       do {} while ( 0 )
+#endif /* TRACE_SOFTIRQS */
+
 static void __do_softirq(unsigned long ignore_mask)
 {
     unsigned int i, cpu = smp_processor_id();
@@ -43,6 +95,7 @@ static void __do_softirq(unsigned long ignore_mask)
 
         i = find_first_set_bit(pending);
         clear_bit(i, &softirq_pending(cpu));
+        trace_handler(i, cpu);
         (*softirq_handlers[i])();
     }
 }
@@ -71,6 +124,8 @@ void cpumask_raise_softirq(const cpumask_t *mask, unsigned 
int nr)
     unsigned int cpu, this_cpu = smp_processor_id();
     cpumask_t send_mask, *raise_mask;
 
+    trace_raise_mask(nr, mask);
+
     if ( !per_cpu(batching, this_cpu) || in_irq() )
     {
         cpumask_clear(&send_mask);
@@ -93,6 +148,8 @@ void cpu_raise_softirq(unsigned int cpu, unsigned int nr)
 {
     unsigned int this_cpu = smp_processor_id();
 
+    trace_raise_cpu(nr, cpu);
+
     if ( test_and_set_bit(nr, &softirq_pending(cpu))
          || (cpu == this_cpu)
          || arch_skip_send_event_check(cpu) )
@@ -125,6 +182,7 @@ void cpu_raise_softirq_batch_finish(void)
 
 void raise_softirq(unsigned int nr)
 {
+    trace_raise(nr);
     set_bit(nr, &softirq_pending(smp_processor_id()));
 }
 
diff --git a/xen/include/public/trace.h b/xen/include/public/trace.h
index 50b4fcc..9d065aa 100644
--- a/xen/include/public/trace.h
+++ b/xen/include/public/trace.h
@@ -95,6 +95,7 @@
 
 /* Trace subclasses for Xen internals */
 #define TRC_XEN_RCU         0x01001000   /* RCU traces */
+#define TRC_XEN_SIRQ        0x01002000   /* Traces relating to softirqs */
 
 /* Trace events per class */
 #define TRC_LOST_RECORDS        (TRC_GEN + 1)
@@ -292,6 +293,12 @@
 #define TRC_XEN_RCU_DO_CALLBKS        (TRC_XEN_RCU + 0x7)
 #define TRC_XEN_RCU_PENDING           (TRC_XEN_RCU + 0x8)
 
+/* Trace events for softirqs */
+#define TRC_XEN_SIRQ_HANDLER          (TRC_XEN_SIRQ + 0x1)
+#define TRC_XEN_SIRQ_RAISE_MASK       (TRC_XEN_SIRQ + 0x2)
+#define TRC_XEN_SIRQ_RAISE_CPU        (TRC_XEN_SIRQ + 0x3)
+#define TRC_XEN_SIRQ_RAISE            (TRC_XEN_SIRQ + 0x4)
+
 /*
  * Event Flags
  *


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