lkml.org 
[lkml]   [2020]   [Oct]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 3/3] task_work: use TIF_TASKWORK if available
Date
If the arch supports TIF_TASKWORK, then use that for TWA_SIGNAL as
it's more efficient than using the signal delivery method. This is
especially true on threaded applications, where ->sighand is shared
across threads.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
kernel/task_work.c | 48 ++++++++++++++++++++++++++++++++++------------
1 file changed, 36 insertions(+), 12 deletions(-)

diff --git a/kernel/task_work.c b/kernel/task_work.c
index 613b2d634af8..ae317cfe86b8 100644
--- a/kernel/task_work.c
+++ b/kernel/task_work.c
@@ -5,6 +5,39 @@

static struct callback_head work_exited; /* all we need is ->next == NULL */

+/*
+ * TWA_SIGNAL signaling - use TIF_TASKWORK, if available.
+ */
+static void task_work_signal(struct task_struct *task)
+{
+#ifndef TIF_TASKWORK
+ unsigned long flags;
+
+ /*
+ * Only grab the sighand lock if we don't already have some
+ * task_work pending. This pairs with the smp_store_mb()
+ * in get_signal(), see comment there.
+ */
+ if (!(READ_ONCE(task->jobctl) & JOBCTL_TASK_WORK) &&
+ lock_task_sighand(task, &flags)) {
+ task->jobctl |= JOBCTL_TASK_WORK;
+ signal_wake_up(task, 0);
+ unlock_task_sighand(task, &flags);
+ }
+#else
+ set_tsk_thread_flag(task, TIF_TASKWORK);
+ set_notify_resume(task);
+#endif
+}
+
+static inline void clear_tsk_taskwork(struct task_struct *task)
+{
+#ifdef TIF_TASKWORK
+ if (test_tsk_thread_flag(task, TIF_TASKWORK))
+ clear_tsk_thread_flag(task, TIF_TASKWORK);
+#endif
+}
+
/**
* task_work_add - ask the @task to execute @work->func()
* @task: the task which should run the callback
@@ -28,7 +61,6 @@ int
task_work_add(struct task_struct *task, struct callback_head *work, int notify)
{
struct callback_head *head;
- unsigned long flags;

do {
head = READ_ONCE(task->task_works);
@@ -42,17 +74,7 @@ task_work_add(struct task_struct *task, struct callback_head *work, int notify)
set_notify_resume(task);
break;
case TWA_SIGNAL:
- /*
- * Only grab the sighand lock if we don't already have some
- * task_work pending. This pairs with the smp_store_mb()
- * in get_signal(), see comment there.
- */
- if (!(READ_ONCE(task->jobctl) & JOBCTL_TASK_WORK) &&
- lock_task_sighand(task, &flags)) {
- task->jobctl |= JOBCTL_TASK_WORK;
- signal_wake_up(task, 0);
- unlock_task_sighand(task, &flags);
- }
+ task_work_signal(task);
break;
}

@@ -110,6 +132,8 @@ void task_work_run(void)
struct task_struct *task = current;
struct callback_head *work, *head, *next;

+ clear_tsk_taskwork(task);
+
for (;;) {
/*
* work->func() can do task_work_add(), do not set
--
2.28.0
\
 
 \ /
  Last update: 2020-10-01 21:42    [W:0.107 / U:1.928 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site