From 71425189b2b75336d869cfdedea45c9d319fc9c9 Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Fri, 4 Dec 2020 20:13:54 +0100 Subject: blk-mq: Don't complete on a remote CPU in force threaded mode 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 Reviewed-by: Christoph Hellwig Reviewed-by: Daniel Wagner Signed-off-by: Jens Axboe --- block/blk-mq.c | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'block') diff --git a/block/blk-mq.c b/block/blk-mq.c index a428798e1c5c..c338c9bc5a2c 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 || -- cgit v1.2.3