From: Paolo Abeni <pab...@redhat.com>
commit e94601d32f4d7fdc28da15a72fe5262c63a5755a in linux-stable-rt
This reverts the following commits:
4cd13c21b207 ("softirq: Let ksoftirqd do its job")
3c53776e29f8 ("Mark HI and TASKLET softirq synchronous")
1342d8080f61 ("softirq: Don't skip softirq execution when softirq thread is
parking")
in a single change to avoid known bad intermediate states introduced by a
patch series reverting them individually.
Due to the mentioned commit, when the ksoftirqd threads take charge of
softirq processing, the system can experience high latencies.
In the past a few workarounds have been implemented for specific
side-effects of the initial ksoftirqd enforcement commit:
commit 1ff688209e2e ("watchdog: core: make sure the watchdog_worker is not
deferred")
commit 8d5755b3f77b ("watchdog: softdog: fire watchdog even if softirqs do not
get to run")
commit 217f69743681 ("net: busy-poll: allow preemption in sk_busy_loop()")
commit 3c53776e29f8 ("Mark HI and TASKLET softirq synchronous")
But the latency problem still exists in real-life workloads, see the link
below.
The reverted commit intended to solve a live-lock scenario that can now be
addressed with the NAPI threaded mode, introduced with commit 29863d41bb6e
("net: implement threaded-able napi poll loop support"), which is nowadays
in a pretty stable status.
While a complete solution to put softirq processing under nice resource
control would be preferable, that has proven to be a very hard task. In
the short term, remove the main pain point, and also simplify a bit the
current softirq implementation.
Signed-off-by: Paolo Abeni <pab...@redhat.com>
Signed-off-by: Thomas Gleixner <t...@linutronix.de>
Tested-by: Jason Xing <kerneljasonx...@gmail.com>
Reviewed-by: Jakub Kicinski <k...@kernel.org>
Reviewed-by: Eric Dumazet <eduma...@google.com>
Reviewed-by: Sebastian Andrzej Siewior <bige...@linutronix.de>
Cc: "Paul E. McKenney" <paul...@kernel.org>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: net...@vger.kernel.org
Link:
https://lore.kernel.org/netdev/305d7742212cbe98621b16be782b0562f1012cb6.ca...@redhat.com
Link:
https://lore.kernel.org/r/57e66b364f1b6f09c9bc0316742c3b14f4ce83bd.1683526542.git.pab...@redhat.com
(cherry picked from commit d15121be7485655129101f3960ae6add40204463)
Signed-off-by: Joseph Salisbury <joseph.salisb...@canonical.com>
Signed-off-by: Paul Gortmaker <paul.gortma...@windriver.com>
---
kernel/softirq.c | 22 ++--------------------
1 file changed, 2 insertions(+), 20 deletions(-)
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 41f470929e99..398951403331 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -80,21 +80,6 @@ static void wakeup_softirqd(void)
wake_up_process(tsk);
}
-/*
- * If ksoftirqd is scheduled, we do not want to process pending softirqs
- * right now. Let ksoftirqd handle this at its own rate, to get fairness,
- * unless we're doing some of the synchronous softirqs.
- */
-#define SOFTIRQ_NOW_MASK ((1 << HI_SOFTIRQ) | (1 << TASKLET_SOFTIRQ))
-static bool ksoftirqd_running(unsigned long pending)
-{
- struct task_struct *tsk = __this_cpu_read(ksoftirqd);
-
- if (pending & SOFTIRQ_NOW_MASK)
- return false;
- return tsk && task_is_running(tsk) && !__kthread_should_park(tsk);
-}
-
#ifdef CONFIG_TRACE_IRQFLAGS
DEFINE_PER_CPU(int, hardirqs_enabled);
DEFINE_PER_CPU(int, hardirq_context);
@@ -236,7 +221,7 @@ void __local_bh_enable_ip(unsigned long ip, unsigned int
cnt)
goto out;
pending = local_softirq_pending();
- if (!pending || ksoftirqd_running(pending))
+ if (!pending)
goto out;
/*
@@ -419,9 +404,6 @@ static inline bool should_wake_ksoftirqd(void)
static inline void invoke_softirq(void)
{
- if (ksoftirqd_running(local_softirq_pending()))
- return;
-
if (!force_irqthreads() || !__this_cpu_read(ksoftirqd)) {
#ifdef CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK
/*
@@ -455,7 +437,7 @@ asmlinkage __visible void do_softirq(void)
pending = local_softirq_pending();
- if (pending && !ksoftirqd_running(pending))
+ if (pending)
do_softirq_own_stack();
local_irq_restore(flags);
--
2.40.0
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