| Message ID | 20201204191356.2516405-2-bigeasy@linutronix.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | blk-mq: Don't complete in IRQ, use llist_head | expand |
On Fri, Dec 04, 2020 at 08:13:54PM +0100, Sebastian Andrzej Siewior wrote: > With force threaded interrupts enabled, raising softirq from an SMP > function call will always result in waking the ksoftirqd thread. This is > not optimal given that the thread runs at SCHED_OTHER priority. > > Completing the request in hard IRQ-context on PREEMPT_RT (which enforces > the force threaded mode) is bad because the completion handler may > acquire sleeping locks which violate the locking context. > > Disable request completing on a remote CPU in force threaded mode. > > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Looks good, Reviewed-by: Christoph Hellwig <hch@lst.de>
diff --git a/block/blk-mq.c b/block/blk-mq.c index b9c2efab5db78..7091bb097c63f 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -650,6 +650,14 @@ static inline bool blk_mq_complete_need_ipi(struct request *rq) if (!IS_ENABLED(CONFIG_SMP) || !test_bit(QUEUE_FLAG_SAME_COMP, &rq->q->queue_flags)) return false; + /* + * With force threaded interrupts enabled, raising softirq from an SMP + * function call will always result in waking the ksoftirqd thread. + * This is probably worse than completing the request on a different + * cache domain. + */ + if (force_irqthreads) + return false; /* same CPU or cache domain? Complete locally */ if (cpu == rq->mq_ctx->cpu ||
With force threaded interrupts enabled, raising softirq from an SMP function call will always result in waking the ksoftirqd thread. This is not optimal given that the thread runs at SCHED_OTHER priority. Completing the request in hard IRQ-context on PREEMPT_RT (which enforces the force threaded mode) is bad because the completion handler may acquire sleeping locks which violate the locking context. Disable request completing on a remote CPU in force threaded mode. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- block/blk-mq.c | 8 ++++++++ 1 file changed, 8 insertions(+)