| Message ID | YrF1p2n0MxHQ3fcJ@linutronix.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [REPOST] blk-mq: Don't disable preemption around __blk_mq_run_hw_queue(). | expand |
On Tue, Jun 21, 2022 at 09:39:19AM +0200, Sebastian Andrzej Siewior wrote: > __blk_mq_delay_run_hw_queue() disables preemption to get a stable > current CPU number and then invokes __blk_mq_run_hw_queue() if the CPU > number is part the mask. > > __blk_mq_run_hw_queue() acquires a spin_lock_t which is a sleeping lock > on PREEMPT_RT and can't be acquired with disabled preemption. > > If it is important that the current CPU matches the requested CPU mask > and that the context does not migrate to another CPU while > __blk_mq_run_hw_queue() is invoked then it possible to achieve this by > disabling migration and keeping the context preemptible. > > Disable only migration while testing the CPU mask and invoking > __blk_mq_run_hw_queue(). > > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> > Link: https://lore.kernel.org/r/YnQHqx/5+54jd+U+@linutronix.de > Link: https://lore.kernel.org/r/YqISXf6GAQeWqcR+@linutronix.de > --- > block/blk-mq.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -2083,14 +2083,14 @@ static void __blk_mq_delay_run_hw_queue( > return; > > if (!async && !(hctx->flags & BLK_MQ_F_BLOCKING)) { > - int cpu = get_cpu(); > - if (cpumask_test_cpu(cpu, hctx->cpumask)) { > + migrate_disable(); > + if (cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask)) { > __blk_mq_run_hw_queue(hctx); > - put_cpu(); > + migrate_enable(); I think you can replace it with raw_smp_processor_id() directly without disabling migration. Both async run queue and direct issue can run on cpu not on hctx->cpumask, so it is fine for sync run queue too. Thanks, Ming
--- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2083,14 +2083,14 @@ static void __blk_mq_delay_run_hw_queue( return; if (!async && !(hctx->flags & BLK_MQ_F_BLOCKING)) { - int cpu = get_cpu(); - if (cpumask_test_cpu(cpu, hctx->cpumask)) { + migrate_disable(); + if (cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask)) { __blk_mq_run_hw_queue(hctx); - put_cpu(); + migrate_enable(); return; } - put_cpu(); + migrate_enable(); } kblockd_mod_delayed_work_on(blk_mq_hctx_next_cpu(hctx), &hctx->run_work,
__blk_mq_delay_run_hw_queue() disables preemption to get a stable current CPU number and then invokes __blk_mq_run_hw_queue() if the CPU number is part the mask. __blk_mq_run_hw_queue() acquires a spin_lock_t which is a sleeping lock on PREEMPT_RT and can't be acquired with disabled preemption. If it is important that the current CPU matches the requested CPU mask and that the context does not migrate to another CPU while __blk_mq_run_hw_queue() is invoked then it possible to achieve this by disabling migration and keeping the context preemptible. Disable only migration while testing the CPU mask and invoking __blk_mq_run_hw_queue(). Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Link: https://lore.kernel.org/r/YnQHqx/5+54jd+U+@linutronix.de Link: https://lore.kernel.org/r/YqISXf6GAQeWqcR+@linutronix.de --- block/blk-mq.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)