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2014-07-01blk-mq: use percpu_ref for mq usage countTejun Heo
Currently, blk-mq uses a percpu_counter to keep track of how many usages are in flight. The percpu_counter is drained while freezing to ensure that no usage is left in-flight after freezing is complete. blk_mq_queue_enter/exit() and blk_mq_[un]freeze_queue() implement this per-cpu gating mechanism. This type of code has relatively high chance of subtle bugs which are extremely difficult to trigger and it's way too hairy to be open coded in blk-mq. percpu_ref can serve the same purpose after the recent changes. This patch replaces the open-coded per-cpu usage counting and draining mechanism with percpu_ref. blk_mq_queue_enter() performs tryget_live on the ref and exit() performs put. blk_mq_freeze_queue() kills the ref and waits until the reference count reaches zero. blk_mq_unfreeze_queue() revives the ref and wakes up the waiters. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Nicholas A. Bellinger <nab@linux-iscsi.org> Cc: Kent Overstreet <kmo@daterainc.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-07-01blk-mq: collapse __blk_mq_drain_queue() into blk_mq_freeze_queue()Tejun Heo
Keeping __blk_mq_drain_queue() as a separate function doesn't buy us anything and it's gonna be further simplified. Let's flatten it into its caller. This patch doesn't make any functional change. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Nicholas A. Bellinger <nab@linux-iscsi.org> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-07-01blk-mq: decouble blk-mq freezing from generic bypassingTejun Heo
blk_mq freezing is entangled with generic bypassing which bypasses blkcg and io scheduler and lets IO requests fall through the block layer to the drivers in FIFO order. This allows forward progress on IOs with the advanced features disabled so that those features can be configured or altered without worrying about stalling IO which may lead to deadlock through memory allocation. However, generic bypassing doesn't quite fit blk-mq. blk-mq currently doesn't make use of blkcg or ioscheds and it maps bypssing to freezing, which blocks request processing and drains all the in-flight ones. This causes problems as bypassing assumes that request processing is online. blk-mq works around this by conditionally allowing request processing for the problem case - during queue initialization. Another weirdity is that except for during queue cleanup, bypassing started on the generic side prevents blk-mq from processing new requests but doesn't drain the in-flight ones. This shouldn't break anything but again highlights that something isn't quite right here. The root cause is conflating blk-mq freezing and generic bypassing which are two different mechanisms. The only intersecting purpose that they serve is during queue cleanup. Let's properly separate blk-mq freezing from generic bypassing and simply use it where necessary. * request_queue->mq_freeze_depth is added and blk_mq_[un]freeze_queue() now operate on this counter instead of ->bypass_depth. The replacement for QUEUE_FLAG_BYPASS isn't added but the counter is tested directly. This will be further updated by later changes. * blk_mq_drain_queue() is dropped and "__" prefix is dropped from blk_mq_freeze_queue(). Queue cleanup path now calls blk_mq_freeze_queue() directly. * blk_queue_enter()'s fast path condition is simplified to simply check @q->mq_freeze_depth. Previously, the condition was !blk_queue_dying(q) && (!blk_queue_bypass(q) || !blk_queue_init_done(q)) mq_freeze_depth is incremented right after dying is set and blk_queue_init_done() exception isn't necessary as blk-mq doesn't start frozen, which only leaves the blk_queue_bypass() test which can be replaced by @q->mq_freeze_depth test. This change simplifies the code and reduces confusion in the area. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Nicholas A. Bellinger <nab@linux-iscsi.org> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-07-01block, blk-mq: draining can't be skipped even if bypass_depth was non-zeroTejun Heo
Currently, both blk_queue_bypass_start() and blk_mq_freeze_queue() skip queue draining if bypass_depth was already above zero. The assumption is that the one which bumped the bypass_depth should have performed draining already; however, there's nothing which prevents a new instance of bypassing/freezing from starting before the previous one finishes draining. The current code may allow the later bypassing/freezing instances to complete while there still are in-flight requests which haven't finished draining. Fix it by draining regardless of bypass_depth. We still skip draining from blk_queue_bypass_start() while the queue is initializing to avoid introducing excessive delays during boot. INIT_DONE setting is moved above the initial blk_queue_bypass_end() so that bypassing attempts can't slip inbetween. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Nicholas A. Bellinger <nab@linux-iscsi.org> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-07-01blk-mq: fix a memory ordering bug in blk_mq_queue_enter()Tejun Heo
blk-mq uses a percpu_counter to keep track of how many usages are in flight. The percpu_counter is drained while freezing to ensure that no usage is left in-flight after freezing is complete. blk_mq_queue_enter/exit() and blk_mq_[un]freeze_queue() implement this per-cpu gating mechanism; unfortunately, it contains a subtle bug - smp_wmb() in blk_mq_queue_enter() doesn't prevent prevent the cpu from fetching @q->bypass_depth before incrementing @q->mq_usage_counter and if freezing happens inbetween the caller can slip through and freezing can be complete while there are active users. Use smp_mb() instead so that bypass_depth and mq_usage_counter modifications and tests are properly interlocked. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Nicholas A. Bellinger <nab@linux-iscsi.org> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-06-25blk-mq: blk_mq_start_hw_queue() should use blk_mq_run_hw_queue()Jens Axboe
Currently it calls __blk_mq_run_hw_queue(), which depends on the CPU placement being correct. This means it's not possible to call blk_mq_start_hw_queues(q) from a context that is correct for all queues, leading to triggering the WARN_ON(!cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask)); in __blk_mq_run_hw_queue(). Reported-by: Ming Lei <tom.leiming@gmail.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-06-13blk-mq: merge blk_mq_drain_queue and __blk_mq_drain_queueChristoph Hellwig
Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-06-13blk-mq: properly drain stopped queuesChristoph Hellwig
If we need to drain a queue we need to run all queues, even if they are marked stopped to make sure the driver has a chance to error out on all queued requests. This fixes surprise removal with scsi-mq. Reported-by: Bart Van Assche <bvanassche@acm.org> Tested-by: Bart Van Assche <bvanassche@acm.org> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-06-09blk-mq: add timer in blk_mq_start_requestMing Lei
This way will become consistent with non-mq case, also avoid to update rq->deadline twice for mq. The comment said: "We do this early, to ensure we are on the right CPU.", but no percpu stuff is used in blk_add_timer(), so it isn't necessary. Even when inserting from plug list, there is no such guarantee at all. Signed-off-by: Ming Lei <tom.leiming@gmail.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-06-09blk-mq: always initialize request->start_timeJens Axboe
The blk-mq core only initializes this if io stats are enabled, since blk-mq only reads the field in that case. But drivers could potentially use it internally, so ensure that we always set it to the current time when the request is allocated. Reported-by: Ming Lei <tom.leiming@gmail.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-06-06blk-mq: ->timeout should be cleared in blk_mq_rq_ctx_init()Jens Axboe
It'll be used in blk_mq_start_request() to set a potential timeout for the request, so clear it to zero at alloc time to ensure that we know if someone has set it or not. Fixes random early timeouts on NVMe testing. Signed-off-by: Jens Axboe <axboe@fb.com>
2014-06-06blk-mq: don't allow queue entering for a dying queueKeith Busch
If the queue is going away, don't let new allocs or queueing happen on it. Go through the normal wait process, and exit with ENODEV in that case. Signed-off-by: Keith Busch <keith.busch@intel.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-06-06blk-mq: bump max tag depth to 10K tagsJens Axboe
For some scsi-mq cases, the tag map can be huge. So increase the max number of tags we support. Additionally, don't fail with EINVAL if a user requests too many tags. Warn that the tag depth has been adjusted down, and store the new value inside the tag_set passed in. Signed-off-by: Jens Axboe <axboe@fb.com>
2014-06-04blk-mq: let blk_mq_tag_to_rq() take blk_mq_tags as the main parameterJens Axboe
We currently pass in the hardware queue, and get the tags from there. But from scsi-mq, with a shared tag space, it's a lot more convenient to pass in the blk_mq_tags instead as the hardware queue isn't always directly available. So instead of having to re-map to a given hardware queue from rq->mq_ctx, just pass in the tags structure. Signed-off-by: Jens Axboe <axboe@fb.com>
2014-06-04blk-mq: fix regression from commit 624dbe475416Jens Axboe
When the code was collapsed to avoid duplication, the recent patch for ensuring that a queue is idled before free was dropped, which was added by commit 19c5d84f14d2. Add back the blk_mq_tag_idle(), to ensure we don't leak a reference to an active queue when it is freed. Signed-off-by: Jens Axboe <axboe@fb.com>
2014-06-03blk-mq: handle NULL req return from blk_map_request in single queue modeJens Axboe
blk_mq_map_request() can return NULL if we fail entering the queue (dying, or removed), in which case it has already ended IO on the bio. So nothing more to do, except just return. Signed-off-by: Jens Axboe <axboe@fb.com>
2014-06-03blk-mq: fix sparse warning on missed __percpu annotationMing Lei
'struct blk_mq_ctx' is __percpu, so add the annotation and fix the sparse warning reported from Fengguang: [block:for-linus 2/3] block/blk-mq.h:75:16: sparse: incorrect type in initializer (different address spaces) Reported-by: kbuild test robot <fengguang.wu@intel.com> Signed-off-by: Ming Lei <tom.leiming@gmail.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-06-03blk-mq: fix schedule from atomic contextMing Lei
blk_mq_put_ctx() has to be called before io_schedule() in bt_get(). This patch fixes the problem by taking similar approach from percpu_ida allocation for the situation. Signed-off-by: Ming Lei <tom.leiming@gmail.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-06-03blk-mq: move blk_mq_get_ctx/blk_mq_put_ctx to mq private headerMing Lei
The blk-mq tag code need these helpers. Signed-off-by: Ming Lei <tom.leiming@gmail.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-30blk-mq: push IPI or local end_io decision to __blk_mq_complete_request()Jens Axboe
We have callers outside of the blk-mq proper (like timeouts) that want to call __blk_mq_complete_request(), so rename the function and put the decision code for whether to use ->softirq_done_fn or blk_mq_endio() into __blk_mq_complete_request(). This also makes the interface more logical again. blk_mq_complete_request() attempts to atomically mark the request completed, and calls __blk_mq_complete_request() if successful. __blk_mq_complete_request() then just ends the request. Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-30blk-mq: remember to start timeout handler for direct queueJens Axboe
Commit 07068d5b8e added a direct-to-hw-queue mode, but this mode needs to remember to add the request timeout handler as well. Without it, we don't track timeouts for these requests. Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-30blk-mq: make the sysfs mq/ layout reflect current mappingsJens Axboe
Currently blk-mq registers all the hardware queues in sysfs, regardless of whether it uses them (e.g. they have CPU mappings) or not. The unused hardware queues lack the cpux/ directories, and the other sysfs entries (like active, pending, etc) are all zeroes. Change this so that sysfs correctly reflects the current mappings of the hardware queues. Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-30blk-mq: blk_mq_tag_to_rq should handle flush requestShaohua Li
flush request is special, which borrows the tag from the parent request. Hence blk_mq_tag_to_rq needs special handling to return the flush request from the tag. Signed-off-by: Shaohua Li <shli@fusionio.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-29blk-mq: request initialization optimizationsJens Axboe
We currently clear a lot more than we need to, so make that a bit more clever. Make some of the init dependent on features, like only setting start_time if we are going to use it. Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-29block: add queue flag for disabling SG mergingJens Axboe
If devices are not SG starved, we waste a lot of time potentially collapsing SG segments. Enough that 1.5% of the CPU time goes to this, at only 400K IOPS. Add a queue flag, QUEUE_FLAG_NO_SG_MERGE, which just returns the number of vectors in a bio instead of looping over all segments and checking for collapsible ones. Add a BLK_MQ_F_SG_MERGE flag so that drivers can opt-in on the sg merging, if they so desire. Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-28blk-mq: remove alloc_hctx and free_hctx methodsChristoph Hellwig
There is no need for drivers to control hardware context allocation now that we do the context to node mapping in common code. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-28blk-mq: add file comments and update copyright noticesJens Axboe
None of the blk-mq files have an explanatory comment at the top for what that particular file does. Add that and add appropriate copyright notices as well. Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-28blk-mq: remove blk_mq_alloc_request_pinnedChristoph Hellwig
We now only have one caller left and can open code it there in a cleaner way. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-28blk-mq: do not use blk_mq_alloc_request_pinned in blk_mq_map_requestChristoph Hellwig
We already do a non-blocking allocation in blk_mq_map_request, no need to repeat it. Just call __blk_mq_alloc_request to wait directly. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-28blk-mq: remove blk_mq_wait_for_tagsChristoph Hellwig
The current logic for blocking tag allocation is rather confusing, as we first allocated and then free again a tag in blk_mq_wait_for_tags, just to attempt a non-blocking allocation and then repeat if someone else managed to grab the tag before us. Instead change blk_mq_alloc_request_pinned to simply do a blocking tag allocation itself and use the request we get back from it. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-28blk-mq: initialize request in __blk_mq_alloc_requestChristoph Hellwig
Both callers if __blk_mq_alloc_request want to initialize the request, so lift it into the common path. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-28blk-mq: merge blk_mq_alloc_reserved_request into blk_mq_alloc_requestChristoph Hellwig
Instead of having two almost identical copies of the same code just let the callers pass in the reserved flag directly. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-28blk-mq: add helper to insert requests from irq contextChristoph Hellwig
Both the cache flush state machine and the SCSI midlayer want to submit requests from irq context, and the current per-request requeue_work unfortunately causes corruption due to sharing with the csd field for flushes. Replace them with a per-request_queue list of requests to be requeued. Based on an earlier test by Ming Lei. Signed-off-by: Christoph Hellwig <hch@lst.de> Reported-by: Ming Lei <tom.leiming@gmail.com> Tested-by: Ming Lei <tom.leiming@gmail.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-27blk-mq: allow non-softirq completionsJens Axboe
Right now we export two ways of completing a request: 1) blk_mq_complete_request(). This uses an IPI (if needed) and completes through q->softirq_done_fn(). It also works with timeouts. 2) blk_mq_end_io(). This completes inline, and ignores any timeout state of the request. Let blk_mq_complete_request() handle non-softirq_done_fn completions as well, by just completing inline. If a driver has enough completion ports to place completions correctly, it need not define a mq_ops->complete() and we can avoid an indirect function call by doing the completion inline. Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-27blk-mq: pass in suggested NUMA node to ->alloc_hctx()Jens Axboe
Drivers currently have to figure this out on their own, and they are missing information to do it properly. The ones that did attempt to do it, do it wrong. So just pass in the suggested node directly to the alloc function. Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-27block: only allocate/free mq_usage_counter in blk-mqMing Lei
The percpu counter is only used for blk-mq, so move its allocation and free inside blk-mq, and don't allocate it for legacy queue device. Signed-off-by: Ming Lei <tom.leiming@gmail.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-27blk-mq: avoid code duplicationMing Lei
blk_mq_exit_hw_queues() and blk_mq_free_hw_queues() are introduced to avoid code duplication. Signed-off-by: Ming Lei <tom.leiming@gmail.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-27blk-mq: fix leak of hctx->ctx_mapMing Lei
hctx->ctx_map should have been freed inside blk_mq_free_queue(). Signed-off-by: Ming Lei <tom.leiming@gmail.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-26blk-mq: idle all hardware contexts before freeing a queueChristoph Hellwig
Without this we can leak the active_queues reference if a command is freed while it is considered active. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-23blk-mq: allow setting of per-request timeoutsJens Axboe
Currently blk-mq uses the queue timeout for all requests. But for some commands, drivers may want to set a specific timeout for special requests. Allow this to be passed in through request->timeout, and use it if set. Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-22blk-mq: split make request handler for multi and single queueJens Axboe
We want slightly different behavior from them: - On single queue devices, we currently use the per-process plug for deferred IO and for merging. - On multi queue devices, we don't use the per-process plug, but we want to go straight to hardware for SYNC IO. Split blk_mq_make_request() into a blk_sq_make_request() for single queue devices, and retain blk_mq_make_request() for multi queue devices. Then we don't need multiple checks for q->nr_hw_queues in the request mapping. Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-21blk-mq: save memory by freeing requests on unused hardware queuesJens Axboe
Depending on the topology of the machine and the number of queues exposed by a device, we can end up in a situation where some of the hardware queues are unused (as in, they don't map to any software queues). For this case, free up the memory used by the request map, as we will not use it. This can be a substantial amount of memory, depending on the number of queues vs CPUs and the queue depth of the device. Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-21blk-mq: allow the hctx cpu hotplug notifier to return errorsJens Axboe
Prepare this for the next patch which adds more smarts in the plugging logic, so that we can save some memory. Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-20blk-mq: Micro-optimize blk_queue_nomerges() checkRobert Elliott
In blk_mq_make_request(), do the blk_queue_nomerges() check outside the call to blk_attempt_plug_merge() to eliminate function call overhead when nomerges=2 (disabled) Signed-off-by: Robert Elliott <elliott@hp.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-20blk-mq: initialize q->nr_requests after calling blk_queue_make_request()Jens Axboe
blk_queue_make_requests() overwrites our set value for q->nr_requests, turning it into the default of 128. Set this appropriately after initializing queue values in blk_queue_make_request(). Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-20blk-mq: allow changing of queue depth through sysfsJens Axboe
For request_fn based devices, the block layer exports a 'nr_requests' file through sysfs to allow adjusting of queue depth on the fly. Currently this returns -EINVAL for blk-mq, since it's not wired up. Wire this up for blk-mq, so that it now also always dynamic adjustments of the allowed queue depth for any given block device managed by blk-mq. Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-19Merge branch 'for-3.16/blk-mq-tagging' into for-3.16/coreJens Axboe
Signed-off-by: Jens Axboe <axboe@fb.com> Conflicts: block/blk-mq-tag.c
2014-05-19blk-mq: switch ctx pending map to the sparser blk_align_bitmapJens Axboe
Each hardware queue has a bitmap of software queues with pending requests. When new IO is queued on a software queue, the bit is set, and when IO is pruned on a hardware queue run, the bit is cleared. This causes a lot of traffic. Switch this from the regular BITS_PER_LONG bitmap to a sparser layout, similarly to what was done for blk-mq tagging. 20% performance increase was observed for single threaded IO, and about 15% performanc increase on multiple threads driving the same device. Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-13blk-mq: improve support for shared tags mapsJens Axboe
This adds support for active queue tracking, meaning that the blk-mq tagging maintains a count of active users of a tag set. This allows us to maintain a notion of fairness between users, so that we can distribute the tag depth evenly without starving some users while allowing others to try unfair deep queues. If sharing of a tag set is detected, each hardware queue will track the depth of its own queue. And if this exceeds the total depth divided by the number of active queues, the user is actively throttled down. The active queue count is done lazily to avoid bouncing that data between submitter and completer. Each hardware queue gets marked active when it allocates its first tag, and gets marked inactive when 1) the last tag is cleared, and 2) the queue timeout grace period has passed. Signed-off-by: Jens Axboe <axboe@fb.com>
2014-05-09blk-mq: fix race in IO start accountingJens Axboe
Commit c6d600c6 opened up a small race where we could attempt to account IO completion on a request, racing with IO start accounting. Fix this up by ensuring that we've accounted for IO start before inserting the request. Signed-off-by: Jens Axboe <axboe@fb.com>