diff options
| author | Calvin Owens <calvinowens@fb.com> | 2015-01-13 13:16:18 -0800 |
|---|---|---|
| committer | Luis Henriques <luis.henriques@canonical.com> | 2015-02-24 10:01:04 +0000 |
| commit | 6fb2a4e73a618598f1cf09b5584b8f852686ace6 (patch) | |
| tree | 9db74f6e81d95a59a05f7d245b5fe76bfa95d875 /kernel | |
| parent | 826dcee76905ead374272b731b83fd216f875afc (diff) | |
ksoftirqd: Enable IRQs and call cond_resched() before poking RCU
commit 28423ad283d5348793b0c45cc9b1af058e776fd6 upstream.
While debugging an issue with excessive softirq usage, I encountered the
following note in commit 3e339b5dae24a706 ("softirq: Use hotplug thread
infrastructure"):
[ paulmck: Call rcu_note_context_switch() with interrupts enabled. ]
...but despite this note, the patch still calls RCU with IRQs disabled.
This seemingly innocuous change caused a significant regression in softirq
CPU usage on the sending side of a large TCP transfer (~1 GB/s): when
introducing 0.01% packet loss, the softirq usage would jump to around 25%,
spiking as high as 50%. Before the change, the usage would never exceed 5%.
Moving the call to rcu_note_context_switch() after the cond_sched() call,
as it was originally before the hotplug patch, completely eliminated this
problem.
Signed-off-by: Calvin Owens <calvinowens@fb.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/softirq.c | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/kernel/softirq.c b/kernel/softirq.c index 5918d227730f..f74268fa965e 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -656,9 +656,13 @@ static void run_ksoftirqd(unsigned int cpu) * in the task stack here. */ __do_softirq(); - rcu_note_context_switch(cpu); local_irq_enable(); cond_resched(); + + preempt_disable(); + rcu_note_context_switch(cpu); + preempt_enable(); + return; } local_irq_enable(); |