[PATCH v2 3/5] tasklet: Remove the old-softirq implementation.

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

With the new percpu tasklet (see "tasklet: Introduce per-cpu tasklet."
and "tasklet: Add cross CPU feeding of per-cpu-tasklets") we have
now in a place a working version of per-cpu softirq tasklets.

We can now remove the old implementation of the
softirq tasklet. We also remove the temporary scaffolding
of TASKLET_SOFTIRQ_PERCPU. Further removal of code will
be done in "tasklet: Remove the old scaffolding" once the
schedule tasklet code is in.

This could be squashed in "tasklet: Introduce per-cpu
tasklet for softirq." but the author thought it would
be an easier aid in understanding the code with these
parts split out.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
RFC: First version
v1: Posted, folks asked if ticketlocks fixed it.
v2: Intel confirmed at XPDS 2016 that the problem is still present
    with large guests.

Cc: Jan Beulich <jbeulich@suse.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: "Lan, Tianyu" <tianyu.lan@intel.com>
Cc:  Kevin Tian <kevin.tian@intel.com>
Cc: Jun Nakajima <jun.nakajima@intel.com>
Cc: George Dunlap <George.Dunlap@eu.citrix.com>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Cc: Jan Beulich <jbeulich@suse.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Tim Deegan <tim@xen.org>
Cc: Wei Liu <wei.liu2@citrix.com>
---
 xen/common/tasklet.c      | 35 ++++++-----------------------------
 xen/include/xen/softirq.h |  1 -
 xen/include/xen/tasklet.h |  2 +-
 3 files changed, 7 insertions(+), 31 deletions(-)

diff --git a/xen/common/tasklet.c b/xen/common/tasklet.c
index d8f3cb3..ab23338 100644
--- a/xen/common/tasklet.c
+++ b/xen/common/tasklet.c
@@ -26,7 +26,6 @@ static bool_t tasklets_initialised;
 DEFINE_PER_CPU(unsigned long, tasklet_work_to_do);
 
 static DEFINE_PER_CPU(struct list_head, tasklet_list);
-static DEFINE_PER_CPU(struct list_head, softirq_tasklet_list);
 
 /* Protects all lists and tasklet structures. */
 static DEFINE_SPINLOCK(tasklet_lock);
@@ -56,7 +55,7 @@ static void percpu_tasklet_feed(void *arg)
         dst_list = &__get_cpu_var(softirq_list);
         list_add_tail(&t->list, dst_list);
     }
-    raise_softirq(TASKLET_SOFTIRQ_PERCPU);
+    raise_softirq(TASKLET_SOFTIRQ);
 out:
     spin_unlock_irqrestore(&feeder_lock, flags);
 }
@@ -89,18 +88,14 @@ static void tasklet_enqueue(struct tasklet *t)
 
         list = &__get_cpu_var(softirq_list);
         list_add_tail(&t->list, list);
-        raise_softirq(TASKLET_SOFTIRQ_PERCPU);
+        raise_softirq(TASKLET_SOFTIRQ);
 
         local_irq_restore(flags);
         return;
     }
     if ( t->is_softirq )
     {
-        struct list_head *list = &per_cpu(softirq_tasklet_list, cpu);
-        bool_t was_empty = list_empty(list);
-        list_add_tail(&t->list, list);
-        if ( was_empty )
-            cpu_raise_softirq(cpu, TASKLET_SOFTIRQ);
+        BUG();
     }
     else
     {
@@ -218,7 +213,7 @@ void do_tasklet_work_percpu(void)
         t->func(t->data);
         tasklet_unlock(t);
         if ( poke )
-            raise_softirq(TASKLET_SOFTIRQ_PERCPU);
+            raise_softirq(TASKLET_SOFTIRQ);
         /* We could reinit the t->list but tasklet_enqueue does it for us. */
         return;
     }
@@ -228,7 +223,7 @@ void do_tasklet_work_percpu(void)
     INIT_LIST_HEAD(&t->list);
     list_add_tail(&t->list, &__get_cpu_var(softirq_list));
     smp_wmb();
-    raise_softirq(TASKLET_SOFTIRQ_PERCPU);
+    raise_softirq(TASKLET_SOFTIRQ);
     local_irq_enable();
 }
 
@@ -259,24 +254,9 @@ void do_tasklet(void)
     spin_unlock_irq(&tasklet_lock);
 }
 
-/* Softirq context work */
-static void tasklet_softirq_action(void)
-{
-    unsigned int cpu = smp_processor_id();
-    struct list_head *list = &per_cpu(softirq_tasklet_list, cpu);
-
-    spin_lock_irq(&tasklet_lock);
-
-    do_tasklet_work(cpu, list);
-
-    if ( !list_empty(list) && !cpu_is_offline(cpu) )
-        raise_softirq(TASKLET_SOFTIRQ);
-
-    spin_unlock_irq(&tasklet_lock);
-}
 
 /* Per CPU softirq context work. */
-static void tasklet_softirq_percpu_action(void)
+static void tasklet_softirq_action(void)
 {
     do_tasklet_work_percpu();
 }
@@ -365,14 +345,12 @@ static int cpu_callback(
     {
     case CPU_UP_PREPARE:
         INIT_LIST_HEAD(&per_cpu(tasklet_list, cpu));
-        INIT_LIST_HEAD(&per_cpu(softirq_tasklet_list, cpu));
         INIT_LIST_HEAD(&per_cpu(softirq_list, cpu));
         INIT_LIST_HEAD(&per_cpu(tasklet_feeder, cpu));
         break;
     case CPU_UP_CANCELED:
     case CPU_DEAD:
         migrate_tasklets_from_cpu(cpu, &per_cpu(tasklet_list, cpu));
-        migrate_tasklets_from_cpu(cpu, &per_cpu(softirq_tasklet_list, cpu));
         migrate_tasklets_from_cpu(cpu, &per_cpu(softirq_list, cpu));
         migrate_tasklets_from_cpu(cpu, &per_cpu(tasklet_feeder, cpu));
         break;
@@ -394,7 +372,6 @@ void __init tasklet_subsys_init(void)
     cpu_callback(&cpu_nfb, CPU_UP_PREPARE, hcpu);
     register_cpu_notifier(&cpu_nfb);
     open_softirq(TASKLET_SOFTIRQ, tasklet_softirq_action);
-    open_softirq(TASKLET_SOFTIRQ_PERCPU, tasklet_softirq_percpu_action);
     tasklets_initialised = 1;
 }
 
diff --git a/xen/include/xen/softirq.h b/xen/include/xen/softirq.h
index 6dda1ba..0895a16 100644
--- a/xen/include/xen/softirq.h
+++ b/xen/include/xen/softirq.h
@@ -7,7 +7,6 @@ enum {
     SCHEDULE_SOFTIRQ,
     NEW_TLBFLUSH_CLOCK_PERIOD_SOFTIRQ,
     RCU_SOFTIRQ,
-    TASKLET_SOFTIRQ_PERCPU,
     TASKLET_SOFTIRQ,
     NR_COMMON_SOFTIRQS
 };
diff --git a/xen/include/xen/tasklet.h b/xen/include/xen/tasklet.h
index 530a5e7..21efe7b 100644
--- a/xen/include/xen/tasklet.h
+++ b/xen/include/xen/tasklet.h
@@ -34,7 +34,7 @@ struct tasklet
 #define DECLARE_TASKLET(name, func, data)               \
     _DECLARE_TASKLET(name, func, data, 0, 0)
 #define DECLARE_SOFTIRQ_TASKLET(name, func, data)       \
-    _DECLARE_TASKLET(name, func, data, 1, 0)
+    _DECLARE_TASKLET(name, func, data, 1, 1)
 
 /* Indicates status of tasklet work on each CPU. */
 DECLARE_PER_CPU(unsigned long, tasklet_work_to_do);
-- 
2.4.11


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