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From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Frederic Weisbecker <frederic@kernel.org>,
	Paul McKenney <paulmck@kernel.org>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: [patch V2 1/9] softirq: Add RT specific softirq accounting
Date: Fri, 04 Dec 2020 18:01:52 +0100	[thread overview]
Message-ID: <20201204170804.765109984@linutronix.de> (raw)
In-Reply-To: 20201204170151.960336698@linutronix.de

From: Thomas Gleixner <tglx@linutronix.de>

RT requires the softirq processing and local bottomhalf disabled regions to
be preemptible. Using the normal preempt count based serialization is
therefore not possible because this implicitely disables preemption.

RT kernels use a per CPU local lock to serialize bottomhalfs. As
local_bh_disable() can nest the lock can only be acquired on the outermost
invocation of local_bh_disable() and released when the nest count becomes
zero. Tasks which hold the local lock can be preempted so its required to
keep track of the nest count per task.

Add a RT only counter to task struct and adjust the relevant macros in
preempt.h.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
V2: Rewrote changelog.
---
 include/linux/hardirq.h |    1 +
 include/linux/preempt.h |    6 +++++-
 include/linux/sched.h   |    3 +++
 3 files changed, 9 insertions(+), 1 deletion(-)

--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h
@@ -6,6 +6,7 @@
 #include <linux/preempt.h>
 #include <linux/lockdep.h>
 #include <linux/ftrace_irq.h>
+#include <linux/sched.h>
 #include <linux/vtime.h>
 #include <asm/hardirq.h>
 
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -79,7 +79,11 @@
 
 #define nmi_count()	(preempt_count() & NMI_MASK)
 #define hardirq_count()	(preempt_count() & HARDIRQ_MASK)
-#define softirq_count()	(preempt_count() & SOFTIRQ_MASK)
+#ifdef CONFIG_PREEMPT_RT
+# define softirq_count()	(current->softirq_disable_cnt & SOFTIRQ_MASK)
+#else
+# define softirq_count()	(preempt_count() & SOFTIRQ_MASK)
+#endif
 #define irq_count()	(nmi_count() | hardirq_count() | softirq_count())
 
 /*
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1004,6 +1004,9 @@ struct task_struct {
 	int				softirq_context;
 	int				irq_config;
 #endif
+#ifdef CONFIG_PREEMPT_RT
+	int				softirq_disable_cnt;
+#endif
 
 #ifdef CONFIG_LOCKDEP
 # define MAX_LOCK_DEPTH			48UL


  reply	other threads:[~2020-12-04 17:10 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-04 17:01 [patch V2 0/9] softirq: Make it RT aware Thomas Gleixner
2020-12-04 17:01 ` Thomas Gleixner [this message]
2020-12-07 13:06   ` [patch V2 1/9] softirq: Add RT specific softirq accounting Frederic Weisbecker
2020-12-04 17:01 ` [patch V2 2/9] irqtime: Make accounting correct on RT Thomas Gleixner
2020-12-07  0:23   ` Frederic Weisbecker
2020-12-07  0:57     ` Thomas Gleixner
2020-12-07  1:14       ` Frederic Weisbecker
2020-12-07 13:27   ` Frederic Weisbecker
2020-12-07 14:44     ` Thomas Gleixner
2020-12-04 17:01 ` [patch V2 3/9] softirq: Move various protections into inline helpers Thomas Gleixner
2020-12-07 13:37   ` Frederic Weisbecker
2020-12-04 17:01 ` [patch V2 4/9] softirq: Make softirq control and processing RT aware Thomas Gleixner
2020-12-07 14:16   ` Frederic Weisbecker
2020-12-07 15:08     ` Thomas Gleixner
2020-12-08  0:08   ` Frederic Weisbecker
2020-12-09 10:11   ` Peter Zijlstra
2020-12-09 12:36     ` Thomas Gleixner
2020-12-09 12:42       ` Peter Zijlstra
2020-12-09 13:30         ` Thomas Gleixner
2020-12-09 10:34   ` Peter Zijlstra
2020-12-04 17:01 ` [patch V2 5/9] tick/sched: Prevent false positive softirq pending warnings on RT Thomas Gleixner
2020-12-08 12:23   ` Frederic Weisbecker
2020-12-04 17:01 ` [patch V2 6/9] rcu: Prevent false positive softirq warning " Thomas Gleixner
2020-12-04 17:59   ` Paul E. McKenney
2020-12-04 17:01 ` [patch V2 7/9] softirq: Replace barrier() with cpu_relax() in tasklet_unlock_wait() Thomas Gleixner
2020-12-07 11:39   ` Peter Zijlstra
2020-12-07 15:21     ` Thomas Gleixner
2020-12-04 17:01 ` [patch V2 8/9] tasklets: Use static inlines for stub implementations Thomas Gleixner
2020-12-04 17:02 ` [patch V2 9/9] tasklets: Prevent kill/unlock_wait deadlock on RT Thomas Gleixner
2020-12-07 11:47   ` Peter Zijlstra
2020-12-07 14:00     ` Sebastian Andrzej Siewior
2020-12-07 14:27       ` Peter Zijlstra
2020-12-07 17:55         ` Thomas Gleixner
2020-12-07 15:22       ` Thomas Gleixner
2020-12-07 15:39         ` Sebastian Andrzej Siewior
2020-12-07 17:49           ` Thomas Gleixner
2020-12-07 17:50             ` Thomas Gleixner
2020-12-06 10:05 ` [patch V2 0/9] softirq: Make it RT aware Sebastian Andrzej Siewior

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