This patch changes percpu_ida_alloc() + callers to accept task state
bitmask for prepare_to_wait() for code like target/iscsi that needs
it for interruptible sleep, that is provided in a subsequent patch.

It now expects TASK_UNINTERRUPTIBLE when the caller is able to sleep
waiting for a new tag, or TASK_RUNNING when the caller cannot sleep,
and is forced to return a negative value when no tags are available.

v2 changes:
  - Include blk-mq + tcm_fc + vhost/scsi + target/iscsi changes
  - Drop signal_pending_state() call
v3 changes:
  - Only call prepare_to_wait() + finish_wait() when != TASK_RUNNING
    (PeterZ)
Reported-by: NLinus Torvalds <torvalds@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: NKent Overstreet <kmo@daterainc.com>
Cc: <stable@vger.kernel.org> #3.12+
Signed-off-by: NNicholas Bellinger <nab@linux-iscsi.org>

Add an API to return free tags, blk-mq-tag will use it.

Note, this just returns a snapshot of free tags number. blk-mq-tag has
two usages of it. One is for info output for diagnosis. The other is to
quickly check if there are free tags for request dispatch checking.
Neither requires very precise.

Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: NShaohua Li <shli@fusionio.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Add a new API to iterate free ids. blk-mq-tag will use it.

Note, this doesn't guarantee to iterate all free ids restrictly. Caller
should be aware of this. blk-mq uses it to do sanity check for request
timedout, so can tolerate the limitation.

Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: NShaohua Li <shli@fusionio.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Make percpu_ida percpu size/batch configurable. The block-mq-tag will
use it.

After block-mq uses percpu_ida to manage tags, performance is improved.
My test is done in a 2 sockets machine, 12 process cross the 2 sockets.
So if there is lock contention or ipi, should be stressed heavily.
Testing is done for null-blk.

hw_queue_depth	nopatch iops	patch iops
64		~800k/s		~1470k/s
2048		~4470k/s	~4340k/s

Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: NShaohua Li <shli@fusionio.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

Removing unused struct percpu_ida *pool from arguements of
alloc_local_tag, changed it's one use in percpu_ida.c

(nab: Fixed reference of idr.c -> percpu_ida.c)
Signed-Off-By: NNick Swenson <nks@daterainc.com>
Signed-off-by: NNicholas Bellinger <nab@linux-iscsi.org>

Percpu frontend for allocating ids. With percpu allocation (that works),
it's impossible to guarantee it will always be possible to allocate all
nr_tags - typically, some will be stuck on a remote percpu freelist
where the current job can't get to them.

We do guarantee that it will always be possible to allocate at least
(nr_tags / 2) tags - this is done by keeping track of which and how many
cpus have tags on their percpu freelists. On allocation failure if
enough cpus have tags that there could potentially be (nr_tags / 2) tags
stuck on remote percpu freelists, we then pick a remote cpu at random to
steal from.

Note that there's no cpu hotplug notifier - we don't care, because
steal_tags() will eventually get the down cpu's tags. We _could_ satisfy
more allocations if we had a notifier - but we'll still meet our
guarantees and it's absolutely not a correctness issue, so I don't think
it's worth the extra code.

From akpm:

    "It looks OK to me (that's as close as I get to an ack :))

v6 changes:
  - Add #include <linux/cpumask.h> to include/linux/percpu_ida.h to
    make alpha/arc builds happy (Fengguang)
  - Move second (cpu >= nr_cpu_ids) check inside of first check scope
    in steal_tags() (akpm + nab)

v5 changes:
  - Change percpu_ida->cpus_have_tags to cpumask_t (kmo + akpm)
  - Add comment for percpu_ida_cpu->lock + ->nr_free (kmo + akpm)
  - Convert steal_tags() to use cpumask_weight() + cpumask_next() +
    cpumask_first() + cpumask_clear_cpu() (kmo + akpm)
  - Add comment for alloc_global_tags() (kmo + akpm)
  - Convert percpu_ida_alloc() to use cpumask_set_cpu() (kmo + akpm)
  - Convert percpu_ida_free() to use cpumask_set_cpu() (kmo + akpm)
  - Drop percpu_ida->cpus_have_tags allocation in percpu_ida_init()
    (kmo + akpm)
  - Drop percpu_ida->cpus_have_tags kfree in percpu_ida_destroy()
    (kmo + akpm)
  - Add comment for percpu_ida_alloc @ gfp (kmo + akpm)
  - Move to percpu_ida.c + percpu_ida.h (kmo + akpm + nab)

v4 changes:

  - Fix tags.c reference in percpu_ida_init (akpm)
Signed-off-by: NKent Overstreet <kmo@daterainc.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: "Nicholas A. Bellinger" <nab@linux-iscsi.org>
Signed-off-by: NNicholas Bellinger <nab@linux-iscsi.org>