rt-patches/0112-genirq-Allow-disabling-of-softirq-processing-in-irq-.patch

   1 From 317cb092cbabed65d888b6f75dfa2c99a1ebc051 Mon Sep 17 00:00:00 2001
   2 From: Thomas Gleixner <tglx@linutronix.de>
   3 Date: Tue, 31 Jan 2012 13:01:27 +0100
   4 Subject: [PATCH 112/365] genirq: Allow disabling of softirq processing in irq
   5  thread context
   6
   7 The processing of softirqs in irq thread context is a performance gain
   8 for the non-rt workloads of a system, but it's counterproductive for
   9 interrupts which are explicitely related to the realtime
  10 workload. Allow such interrupts to prevent softirq processing in their
  11 thread context.
  12
  13 Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
  14 ---
  15  include/linux/interrupt.h |  2 ++
  16  include/linux/irq.h       |  4 +++-
  17  kernel/irq/manage.c       | 13 ++++++++++++-
  18  kernel/irq/settings.h     | 12 ++++++++++++
  19  kernel/softirq.c          |  9 +++++++++
  20  5 files changed, 38 insertions(+), 2 deletions(-)
  21
  22 diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
  23 index 7033381..47d38a0 100644
  24 --- a/include/linux/interrupt.h
  25 +++ b/include/linux/interrupt.h
  26 @@ -61,6 +61,7 @@
  27   *                interrupt handler after suspending interrupts. For system
  28   *                wakeup devices users need to implement wakeup detection in
  29   *                their interrupt handlers.
  30 + * IRQF_NO_SOFTIRQ_CALL - Do not process softirqs in the irq thread context (RT)
  31   */
  32  #define IRQF_SHARED            0x00000080
  33  #define IRQF_PROBE_SHARED      0x00000100
  34 @@ -74,6 +75,7 @@
  35  #define IRQF_NO_THREAD         0x00010000
  36  #define IRQF_EARLY_RESUME      0x00020000
  37  #define IRQF_COND_SUSPEND      0x00040000
  38 +#define IRQF_NO_SOFTIRQ_CALL   0x00080000
  39
  40  #define IRQF_TIMER             (__IRQF_TIMER | IRQF_NO_SUSPEND | IRQF_NO_THREAD)
  41
  42 diff --git a/include/linux/irq.h b/include/linux/irq.h
  43 index f7cade0..dac9e11 100644
  44 --- a/include/linux/irq.h
  45 +++ b/include/linux/irq.h
  46 @@ -72,6 +72,7 @@ enum irqchip_irq_state;
  47   * IRQ_IS_POLLED               - Always polled by another interrupt. Exclude
  48   *                               it from the spurious interrupt detection
  49   *                               mechanism and from core side polling.
  50 + * IRQ_NO_SOFTIRQ_CALL         - No softirq processing in the irq thread context (RT)
  51   * IRQ_DISABLE_UNLAZY          - Disable lazy irq disable
  52   */
  53  enum {
  54 @@ -99,13 +100,14 @@ enum {
  55         IRQ_PER_CPU_DEVID       = (1 << 17),
  56         IRQ_IS_POLLED           = (1 << 18),
  57         IRQ_DISABLE_UNLAZY      = (1 << 19),
  58 +       IRQ_NO_SOFTIRQ_CALL     = (1 << 20),
  59  };
  60
  61  #define IRQF_MODIFY_MASK       \
  62         (IRQ_TYPE_SENSE_MASK | IRQ_NOPROBE | IRQ_NOREQUEST | \
  63          IRQ_NOAUTOEN | IRQ_MOVE_PCNTXT | IRQ_LEVEL | IRQ_NO_BALANCING | \
  64          IRQ_PER_CPU | IRQ_NESTED_THREAD | IRQ_NOTHREAD | IRQ_PER_CPU_DEVID | \
  65 -        IRQ_IS_POLLED | IRQ_DISABLE_UNLAZY)
  66 +        IRQ_IS_POLLED | IRQ_DISABLE_UNLAZY | IRQ_NO_SOFTIRQ_CALL)
  67
  68  #define IRQ_NO_BALANCING_MASK  (IRQ_PER_CPU | IRQ_NO_BALANCING)
  69
  70 diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
  71 index 8842388..5b1ad63 100644
  72 --- a/kernel/irq/manage.c
  73 +++ b/kernel/irq/manage.c
  74 @@ -940,7 +940,15 @@ irq_forced_thread_fn(struct irq_desc *desc, struct irqaction *action)
  75         local_bh_disable();
  76         ret = action->thread_fn(action->irq, action->dev_id);
  77         irq_finalize_oneshot(desc, action);
  78 -       local_bh_enable();
  79 +       /*
  80 +        * Interrupts which have real time requirements can be set up
  81 +        * to avoid softirq processing in the thread handler. This is
  82 +        * safe as these interrupts do not raise soft interrupts.
  83 +        */
  84 +       if (irq_settings_no_softirq_call(desc))
  85 +               _local_bh_enable();
  86 +       else
  87 +               local_bh_enable();
  88         return ret;
  89  }
  90
  91 @@ -1390,6 +1398,9 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
  92                         irqd_set(&desc->irq_data, IRQD_NO_BALANCING);
  93                 }
  94
  95 +               if (new->flags & IRQF_NO_SOFTIRQ_CALL)
  96 +                       irq_settings_set_no_softirq_call(desc);
  97 +
  98                 /* Set default affinity mask once everything is setup */
  99                 setup_affinity(desc, mask);
 100
 101 diff --git a/kernel/irq/settings.h b/kernel/irq/settings.h
 102 index 320579d..2df2d44 100644
 103 --- a/kernel/irq/settings.h
 104 +++ b/kernel/irq/settings.h
 105 @@ -16,6 +16,7 @@ enum {
 106         _IRQ_PER_CPU_DEVID      = IRQ_PER_CPU_DEVID,
 107         _IRQ_IS_POLLED          = IRQ_IS_POLLED,
 108         _IRQ_DISABLE_UNLAZY     = IRQ_DISABLE_UNLAZY,
 109 +       _IRQ_NO_SOFTIRQ_CALL    = IRQ_NO_SOFTIRQ_CALL,
 110         _IRQF_MODIFY_MASK       = IRQF_MODIFY_MASK,
 111  };
 112
 113 @@ -30,6 +31,7 @@ enum {
 114  #define IRQ_PER_CPU_DEVID      GOT_YOU_MORON
 115  #define IRQ_IS_POLLED          GOT_YOU_MORON
 116  #define IRQ_DISABLE_UNLAZY     GOT_YOU_MORON
 117 +#define IRQ_NO_SOFTIRQ_CALL    GOT_YOU_MORON
 118  #undef IRQF_MODIFY_MASK
 119  #define IRQF_MODIFY_MASK       GOT_YOU_MORON
 120
 121 @@ -40,6 +42,16 @@ irq_settings_clr_and_set(struct irq_desc *desc, u32 clr, u32 set)
 122         desc->status_use_accessors |= (set & _IRQF_MODIFY_MASK);
 123  }
 124
 125 +static inline bool irq_settings_no_softirq_call(struct irq_desc *desc)
 126 +{
 127 +       return desc->status_use_accessors & _IRQ_NO_SOFTIRQ_CALL;
 128 +}
 129 +
 130 +static inline void irq_settings_set_no_softirq_call(struct irq_desc *desc)
 131 +{
 132 +       desc->status_use_accessors |= _IRQ_NO_SOFTIRQ_CALL;
 133 +}
 134 +
 135  static inline bool irq_settings_is_per_cpu(struct irq_desc *desc)
 136  {
 137         return desc->status_use_accessors & _IRQ_PER_CPU;
 138 diff --git a/kernel/softirq.c b/kernel/softirq.c
 139 index 61de6e9..0fd9331 100644
 140 --- a/kernel/softirq.c
 141 +++ b/kernel/softirq.c
 142 @@ -576,6 +576,15 @@ void __local_bh_enable(void)
 143  }
 144  EXPORT_SYMBOL(__local_bh_enable);
 145
 146 +void _local_bh_enable(void)
 147 +{
 148 +       if (WARN_ON(current->softirq_nestcnt == 0))
 149 +               return;
 150 +       if (--current->softirq_nestcnt == 0)
 151 +               migrate_enable();
 152 +}
 153 +EXPORT_SYMBOL(_local_bh_enable);
 154 +
 155  int in_serving_softirq(void)
 156  {
 157         return current->flags & PF_IN_SOFTIRQ;
 158 --
 159 2.7.4
 160