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author | Linus Torvalds <torvalds@linux-foundation.org> | 2019-07-26 10:32:12 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2019-07-26 10:32:12 -0700 |
commit | 04412819652fe30f900d11e96c67b4adfdf17f6b (patch) | |
tree | aed86baef3fd65e6990484a00514f0594d1fdd6c /block/bfq-iosched.c | |
parent | 750c930b085ba56cfac3649e8e0dff72a8c5f8a5 (diff) | |
parent | 9c0b2596f2ac30967af0b8bb9f038b65926a6f00 (diff) | |
download | linux-04412819652fe30f900d11e96c67b4adfdf17f6b.tar.bz2 |
Merge tag 'for-linus-20190726' of git://git.kernel.dk/linux-block
Pull block fixes from Jens Axboe:
- Several io_uring fixes/improvements:
- Blocking fix for O_DIRECT (me)
- Latter page slowness for registered buffers (me)
- Fix poll hang under certain conditions (me)
- Defer sequence check fix for wrapped rings (Zhengyuan)
- Mismatch in async inc/dec accounting (Zhengyuan)
- Memory ordering issue that could cause stall (Zhengyuan)
- Track sequential defer in bytes, not pages (Zhengyuan)
- NVMe pull request from Christoph
- Set of hang fixes for wbt (Josef)
- Redundant error message kill for libahci (Ding)
- Remove unused blk_mq_sched_started_request() and related ops (Marcos)
- drbd dynamic alloc shash descriptor to reduce stack use (Arnd)
- blkcg ->pd_stat() non-debug print (Tejun)
- bcache memory leak fix (Wei)
- Comment fix (Akinobu)
- BFQ perf regression fix (Paolo)
* tag 'for-linus-20190726' of git://git.kernel.dk/linux-block: (24 commits)
io_uring: ensure ->list is initialized for poll commands
Revert "nvme-pci: don't create a read hctx mapping without read queues"
nvme: fix multipath crash when ANA is deactivated
nvme: fix memory leak caused by incorrect subsystem free
nvme: ignore subnqn for ADATA SX6000LNP
drbd: dynamically allocate shash descriptor
block: blk-mq: Remove blk_mq_sched_started_request and started_request
bcache: fix possible memory leak in bch_cached_dev_run()
io_uring: track io length in async_list based on bytes
io_uring: don't use iov_iter_advance() for fixed buffers
block: properly handle IOCB_NOWAIT for async O_DIRECT IO
blk-mq: allow REQ_NOWAIT to return an error inline
io_uring: add a memory barrier before atomic_read
rq-qos: use a mb for got_token
rq-qos: set ourself TASK_UNINTERRUPTIBLE after we schedule
rq-qos: don't reset has_sleepers on spurious wakeups
rq-qos: fix missed wake-ups in rq_qos_throttle
wait: add wq_has_single_sleeper helper
block, bfq: check also in-flight I/O in dispatch plugging
block: fix sysfs module parameters directory path in comment
...
Diffstat (limited to 'block/bfq-iosched.c')
-rw-r--r-- | block/bfq-iosched.c | 67 |
1 files changed, 43 insertions, 24 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 72860325245a..586fcfe227ea 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -3354,38 +3354,57 @@ static void bfq_dispatch_remove(struct request_queue *q, struct request *rq) * there is no active group, then the primary expectation for * this device is probably a high throughput. * - * We are now left only with explaining the additional - * compound condition that is checked below for deciding - * whether the scenario is asymmetric. To explain this - * compound condition, we need to add that the function + * We are now left only with explaining the two sub-conditions in the + * additional compound condition that is checked below for deciding + * whether the scenario is asymmetric. To explain the first + * sub-condition, we need to add that the function * bfq_asymmetric_scenario checks the weights of only - * non-weight-raised queues, for efficiency reasons (see - * comments on bfq_weights_tree_add()). Then the fact that - * bfqq is weight-raised is checked explicitly here. More - * precisely, the compound condition below takes into account - * also the fact that, even if bfqq is being weight-raised, - * the scenario is still symmetric if all queues with requests - * waiting for completion happen to be - * weight-raised. Actually, we should be even more precise - * here, and differentiate between interactive weight raising - * and soft real-time weight raising. + * non-weight-raised queues, for efficiency reasons (see comments on + * bfq_weights_tree_add()). Then the fact that bfqq is weight-raised + * is checked explicitly here. More precisely, the compound condition + * below takes into account also the fact that, even if bfqq is being + * weight-raised, the scenario is still symmetric if all queues with + * requests waiting for completion happen to be + * weight-raised. Actually, we should be even more precise here, and + * differentiate between interactive weight raising and soft real-time + * weight raising. + * + * The second sub-condition checked in the compound condition is + * whether there is a fair amount of already in-flight I/O not + * belonging to bfqq. If so, I/O dispatching is to be plugged, for the + * following reason. The drive may decide to serve in-flight + * non-bfqq's I/O requests before bfqq's ones, thereby delaying the + * arrival of new I/O requests for bfqq (recall that bfqq is sync). If + * I/O-dispatching is not plugged, then, while bfqq remains empty, a + * basically uncontrolled amount of I/O from other queues may be + * dispatched too, possibly causing the service of bfqq's I/O to be + * delayed even longer in the drive. This problem gets more and more + * serious as the speed and the queue depth of the drive grow, + * because, as these two quantities grow, the probability to find no + * queue busy but many requests in flight grows too. By contrast, + * plugging I/O dispatching minimizes the delay induced by already + * in-flight I/O, and enables bfqq to recover the bandwidth it may + * lose because of this delay. * * As a side note, it is worth considering that the above - * device-idling countermeasures may however fail in the - * following unlucky scenario: if idling is (correctly) - * disabled in a time period during which all symmetry - * sub-conditions hold, and hence the device is allowed to - * enqueue many requests, but at some later point in time some - * sub-condition stops to hold, then it may become impossible - * to let requests be served in the desired order until all - * the requests already queued in the device have been served. + * device-idling countermeasures may however fail in the following + * unlucky scenario: if I/O-dispatch plugging is (correctly) disabled + * in a time period during which all symmetry sub-conditions hold, and + * therefore the device is allowed to enqueue many requests, but at + * some later point in time some sub-condition stops to hold, then it + * may become impossible to make requests be served in the desired + * order until all the requests already queued in the device have been + * served. The last sub-condition commented above somewhat mitigates + * this problem for weight-raised queues. */ static bool idling_needed_for_service_guarantees(struct bfq_data *bfqd, struct bfq_queue *bfqq) { return (bfqq->wr_coeff > 1 && - bfqd->wr_busy_queues < - bfq_tot_busy_queues(bfqd)) || + (bfqd->wr_busy_queues < + bfq_tot_busy_queues(bfqd) || + bfqd->rq_in_driver >= + bfqq->dispatched + 4)) || bfq_asymmetric_scenario(bfqd, bfqq); } |