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| author | Paolo Bonzini <pbonzini@redhat.com> | 2014-11-07 23:04:00 +0100 |
|---|---|---|
| committer | Jens Axboe <axboe@fb.com> | 2014-11-11 11:04:49 -0700 |
| commit | 2a90d4aae5509e9cf1ba848c5d0b3458201160a0 (patch) | |
| tree | f327e5db3649df99d7f957ff6932eb7e7b5fc4ed /block | |
| parent | 398205b8391b208f0034a392242867b28ad8af3d (diff) | |
| download | lwn-2a90d4aae5509e9cf1ba848c5d0b3458201160a0.tar.gz lwn-2a90d4aae5509e9cf1ba848c5d0b3458201160a0.zip | |
blk-mq: use get_cpu/put_cpu instead of preempt_disable/preempt_enable
blk-mq is using preempt_disable/enable in order to ensure that the
queue runners are placed on the right CPU. This does not work with
the RT patches, because __blk_mq_run_hw_queue takes a non-raw
spinlock with the preemption-disabled region. If there is contention
on the lock, this violates the rules for preemption-disabled regions.
While this should be easily fixable within the RT patches just by doing
migrate_disable/enable, we can do better and document _why_ this
particular region runs with disabled preemption. After the previous
patch, it is trivial to switch it to get/put_cpu; the RT patches then
can change it to get_cpu_light, which lets virtio-blk run under RT
kernels.
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Reported-by: Clark Williams <williams@redhat.com>
Tested-by: Clark Williams <williams@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'block')
| -rw-r--r-- | block/blk-mq.c | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/block/blk-mq.c b/block/blk-mq.c index 8b309e81ed0f..06ab0683a1f1 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -802,14 +802,14 @@ void blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async) return; if (!async) { - preempt_disable(); - if (cpumask_test_cpu(smp_processor_id(), hctx->cpumask)) { + int cpu = get_cpu(); + if (cpumask_test_cpu(cpu, hctx->cpumask)) { __blk_mq_run_hw_queue(hctx); - preempt_enable(); + put_cpu(); return; } - preempt_enable(); + put_cpu(); } if (hctx->queue->nr_hw_queues == 1) |