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  1. 29 6月, 2010 18 次提交
    • T
      workqueue: implement cpu intensive workqueue · fb0e7beb
      由 Tejun Heo 提交于 
      This patch implements cpu intensive workqueue which can be specified
with WQ_CPU_INTENSIVE flag on creation.  Works queued to a cpu
intensive workqueue don't participate in concurrency management.  IOW,
it doesn't contribute to gcwq->nr_running and thus doesn't delay
excution of other works.

Note that although cpu intensive works won't delay other works, they
can be delayed by other works.  Combine with WQ_HIGHPRI to avoid being
delayed by other works too.

As the name suggests this is useful when using workqueue for cpu
intensive works.  Workers executing cpu intensive works are not
considered for workqueue concurrency management and left for the
scheduler to manage.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
      fb0e7beb
    • T
      workqueue: implement high priority workqueue · 649027d7
      由 Tejun Heo 提交于 
      This patch implements high priority workqueue which can be specified
with WQ_HIGHPRI flag on creation.  A high priority workqueue has the
following properties.

* A work queued to it is queued at the head of the worklist of the
  respective gcwq after other highpri works, while normal works are
  always appended at the end.

* As long as there are highpri works on gcwq->worklist,
  [__]need_more_worker() remains %true and process_one_work() wakes up
  another worker before it start executing a work.

The above two properties guarantee that works queued to high priority
workqueues are dispatched to workers and start execution as soon as
possible regardless of the state of other works.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
      649027d7
    • T
      workqueue: implement several utility APIs · dcd989cb
      由 Tejun Heo 提交于 
      Implement the following utility APIs.

 workqueue_set_max_active()	: adjust max_active of a wq
 workqueue_congested()		: test whether a wq is contested
 work_cpu()			: determine the last / current cpu of a work
 work_busy()			: query whether a work is busy

* Anton Blanchard fixed missing ret initialization in work_busy().
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Anton Blanchard <anton@samba.org>
      dcd989cb
    • T
      workqueue: s/__create_workqueue()/alloc_workqueue()/, and add system workqueues · d320c038
      由 Tejun Heo 提交于 
      This patch makes changes to make new workqueue features available to
its users.

* Now that workqueue is more featureful, there should be a public
  workqueue creation function which takes paramters to control them.
  Rename __create_workqueue() to alloc_workqueue() and make 0
  max_active mean WQ_DFL_ACTIVE.  In the long run, all
  create_workqueue_*() will be converted over to alloc_workqueue().

* To further unify access interface, rename keventd_wq to system_wq
  and export it.

* Add system_long_wq and system_nrt_wq.  The former is to host long
  running works separately (so that flush_scheduled_work() dosen't
  take so long) and the latter guarantees any queued work item is
  never executed in parallel by multiple CPUs.  These will be used by
  future patches to update workqueue users.
Signed-off-by: NTejun Heo <tj@kernel.org>
      d320c038
    • T
      workqueue: increase max_active of keventd and kill current_is_keventd() · b71ab8c2
      由 Tejun Heo 提交于 
      Define WQ_MAX_ACTIVE and create keventd with max_active set to half of
it which means that keventd now can process upto WQ_MAX_ACTIVE / 2 - 1
works concurrently.  Unless some combination can result in dependency
loop longer than max_active, deadlock won't happen and thus it's
unnecessary to check whether current_is_keventd() before trying to
schedule a work.  Kill current_is_keventd().

(Lockdep annotations are broken.  We need lock_map_acquire_read_norecurse())
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Oleg Nesterov <oleg@redhat.com>
      b71ab8c2
    • T
      workqueue: implement concurrency managed dynamic worker pool · e22bee78
      由 Tejun Heo 提交于 
      Instead of creating a worker for each cwq and putting it into the
shared pool, manage per-cpu workers dynamically.

Works aren't supposed to be cpu cycle hogs and maintaining just enough
concurrency to prevent work processing from stalling due to lack of
processing context is optimal.  gcwq keeps the number of concurrent
active workers to minimum but no less.  As long as there's one or more
running workers on the cpu, no new worker is scheduled so that works
can be processed in batch as much as possible but when the last
running worker blocks, gcwq immediately schedules new worker so that
the cpu doesn't sit idle while there are works to be processed.

gcwq always keeps at least single idle worker around.  When a new
worker is necessary and the worker is the last idle one, the worker
assumes the role of "manager" and manages the worker pool -
ie. creates another worker.  Forward-progress is guaranteed by having
dedicated rescue workers for workqueues which may be necessary while
creating a new worker.  When the manager is having problem creating a
new worker, mayday timer activates and rescue workers are summoned to
the cpu and execute works which might be necessary to create new
workers.

Trustee is expanded to serve the role of manager while a CPU is being
taken down and stays down.  As no new works are supposed to be queued
on a dead cpu, it just needs to drain all the existing ones.  Trustee
continues to try to create new workers and summon rescuers as long as
there are pending works.  If the CPU is brought back up while the
trustee is still trying to drain the gcwq from the previous offlining,
the trustee will kill all idles ones and tell workers which are still
busy to rebind to the cpu, and pass control over to gcwq which assumes
the manager role as necessary.

Concurrency managed worker pool reduces the number of workers
drastically.  Only workers which are necessary to keep the processing
going are created and kept.  Also, it reduces cache footprint by
avoiding unnecessarily switching contexts between different workers.

Please note that this patch does not increase max_active of any
workqueue.  All workqueues can still only process one work per cpu.
Signed-off-by: NTejun Heo <tj@kernel.org>
      e22bee78
    • T
      workqueue: implement WQ_NON_REENTRANT · 18aa9eff
      由 Tejun Heo 提交于 
      With gcwq managing all the workers and work->data pointing to the last
gcwq it was on, non-reentrance can be easily implemented by checking
whether the work is still running on the previous gcwq on queueing.
Implement it.
Signed-off-by: NTejun Heo <tj@kernel.org>
      18aa9eff
    • T
      workqueue: carry cpu number in work data once execution starts · 7a22ad75
      由 Tejun Heo 提交于 
      To implement non-reentrant workqueue, the last gcwq a work was
executed on must be reliably obtainable as long as the work structure
is valid even if the previous workqueue has been destroyed.

To achieve this, work->data will be overloaded to carry the last cpu
number once execution starts so that the previous gcwq can be located
reliably.  This means that cwq can't be obtained from work after
execution starts but only gcwq.

Implement set_work_{cwq|cpu}(), get_work_[g]cwq() and
clear_work_data() to set work data to the cpu number when starting
execution, access the overloaded work data and clear it after
cancellation.

queue_delayed_work_on() is updated to preserve the last cpu while
in-flight in timer and other callers which depended on getting cwq
from work after execution starts are converted to depend on gcwq
instead.

* Anton Blanchard fixed compile error on powerpc due to missing
  linux/threads.h include.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Anton Blanchard <anton@samba.org>
      7a22ad75
    • T
      workqueue: make single thread workqueue shared worker pool friendly · 502ca9d8
      由 Tejun Heo 提交于 
      Reimplement st (single thread) workqueue so that it's friendly to
shared worker pool.  It was originally implemented by confining st
workqueues to use cwq of a fixed cpu and always having a worker for
the cpu.  This implementation isn't very friendly to shared worker
pool and suboptimal in that it ends up crossing cpu boundaries often.

Reimplement st workqueue using dynamic single cpu binding and
cwq->limit.  WQ_SINGLE_THREAD is replaced with WQ_SINGLE_CPU.  In a
single cpu workqueue, at most single cwq is bound to the wq at any
given time.  Arbitration is done using atomic accesses to
wq->single_cpu when queueing a work.  Once bound, the binding stays
till the workqueue is drained.

Note that the binding is never broken while a workqueue is frozen.
This is because idle cwqs may have works waiting in delayed_works
queue while frozen.  On thaw, the cwq is restarted if there are any
delayed works or unbound otherwise.

When combined with max_active limit of 1, single cpu workqueue has
exactly the same execution properties as the original single thread
workqueue while allowing sharing of per-cpu workers.
Signed-off-by: NTejun Heo <tj@kernel.org>
      502ca9d8
    • T
      workqueue: reimplement workqueue freeze using max_active · a0a1a5fd
      由 Tejun Heo 提交于 
      Currently, workqueue freezing is implemented by marking the worker
freezeable and calling try_to_freeze() from dispatch loop.
Reimplement it using cwq->limit so that the workqueue is frozen
instead of the worker.

* workqueue_struct->saved_max_active is added which stores the
  specified max_active on initialization.

* On freeze, all cwq->max_active's are quenched to zero.  Freezing is
  complete when nr_active on all cwqs reach zero.

* On thaw, all cwq->max_active's are restored to wq->saved_max_active
  and the worklist is repopulated.

This new implementation allows having single shared pool of workers
per cpu.
Signed-off-by: NTejun Heo <tj@kernel.org>
      a0a1a5fd
    • T
      workqueue: implement per-cwq active work limit · 1e19ffc6
      由 Tejun Heo 提交于 
      Add cwq->nr_active, cwq->max_active and cwq->delayed_work.  nr_active
counts the number of active works per cwq.  A work is active if it's
flushable (colored) and is on cwq's worklist.  If nr_active reaches
max_active, new works are queued on cwq->delayed_work and activated
later as works on the cwq complete and decrement nr_active.

cwq->max_active can be specified via the new @max_active parameter to
__create_workqueue() and is set to 1 for all workqueues for now.  As
each cwq has only single worker now, this double queueing doesn't
cause any behavior difference visible to its users.

This will be used to reimplement freeze/thaw and implement shared
worker pool.
Signed-off-by: NTejun Heo <tj@kernel.org>
      1e19ffc6
    • T
      workqueue: reimplement work flushing using linked works · affee4b2
      由 Tejun Heo 提交于 
      A work is linked to the next one by having WORK_STRUCT_LINKED bit set
and these links can be chained.  When a linked work is dispatched to a
worker, all linked works are dispatched to the worker's newly added
->scheduled queue and processed back-to-back.

Currently, as there's only single worker per cwq, having linked works
doesn't make any visible behavior difference.  This change is to
prepare for multiple shared workers per cpu.
Signed-off-by: NTejun Heo <tj@kernel.org>
      affee4b2
    • T
      workqueue: reimplement workqueue flushing using color coded works · 73f53c4a
      由 Tejun Heo 提交于 
      Reimplement workqueue flushing using color coded works.  wq has the
current work color which is painted on the works being issued via
cwqs.  Flushing a workqueue is achieved by advancing the current work
colors of cwqs and waiting for all the works which have any of the
previous colors to drain.

Currently there are 16 possible colors, one is reserved for no color
and 15 colors are useable allowing 14 concurrent flushes.  When color
space gets full, flush attempts are batched up and processed together
when color frees up, so even with many concurrent flushers, the new
implementation won't build up huge queue of flushers which has to be
processed one after another.

Only works which are queued via __queue_work() are colored.  Works
which are directly put on queue using insert_work() use NO_COLOR and
don't participate in workqueue flushing.  Currently only works used
for work-specific flush fall in this category.

This new implementation leaves only cleanup_workqueue_thread() as the
user of flush_cpu_workqueue().  Just make its users use
flush_workqueue() and kthread_stop() directly and kill
cleanup_workqueue_thread().  As workqueue flushing doesn't use barrier
request anymore, the comment describing the complex synchronization
around it in cleanup_workqueue_thread() is removed together with the
function.

This new implementation is to allow having and sharing multiple
workers per cpu.

Please note that one more bit is reserved for a future work flag by
this patch.  This is to avoid shifting bits and updating comments
later.
Signed-off-by: NTejun Heo <tj@kernel.org>
      73f53c4a
    • T
      workqueue: update cwq alignement · 0f900049
      由 Tejun Heo 提交于 
      work->data field is used for two purposes.  It points to cwq it's
queued on and the lower bits are used for flags.  Currently, two bits
are reserved which is always safe as 4 byte alignment is guaranteed on
every architecture.  However, future changes will need more flag bits.

On SMP, the percpu allocator is capable of honoring larger alignment
(there are other users which depend on it) and larger alignment works
just fine.  On UP, percpu allocator is a thin wrapper around
kzalloc/kfree() and don't honor alignment request.

This patch introduces WORK_STRUCT_FLAG_BITS and implements
alloc/free_cwqs() which guarantees max(1 << WORK_STRUCT_FLAG_BITS,
__alignof__(unsigned long long) alignment both on SMP and UP.  On SMP,
simply wrapping percpu allocator is enough.  On UP, extra space is
allocated so that cwq can be aligned and the original pointer can be
stored after it which is used in the free path.

* Alignment problem on UP is reported by Michal Simek.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Reported-by: NMichal Simek <michal.simek@petalogix.com>
      0f900049
    • T
      workqueue: define masks for work flags and conditionalize STATIC flags · 22df02bb
      由 Tejun Heo 提交于 
      Work flags are about to see more traditional mask handling.  Define
WORK_STRUCT_*_BIT as the bit position constant and redefine
WORK_STRUCT_* as bit masks.  Also, make WORK_STRUCT_STATIC_* flags
conditional

While at it, re-define these constants as enums and use
WORK_STRUCT_STATIC instead of hard-coding 2 in
WORK_DATA_STATIC_INIT().
Signed-off-by: NTejun Heo <tj@kernel.org>
      22df02bb
    • T
      workqueue: merge feature parameters into flags · 97e37d7b
      由 Tejun Heo 提交于 
      Currently, __create_workqueue_key() takes @singlethread and
@freezeable paramters and store them separately in workqueue_struct.
Merge them into a single flags parameter and field and use
WQ_FREEZEABLE and WQ_SINGLE_THREAD.
Signed-off-by: NTejun Heo <tj@kernel.org>
      97e37d7b
    • T
      workqueue: misc/cosmetic updates · 4690c4ab
      由 Tejun Heo 提交于 
      Make the following updates in preparation of concurrency managed
workqueue.  None of these changes causes any visible behavior
difference.

* Add comments and adjust indentations to data structures and several
  functions.

* Rename wq_per_cpu() to get_cwq() and swap the position of two
  parameters for consistency.  Convert a direct per_cpu_ptr() access
  to wq->cpu_wq to get_cwq().

* Add work_static() and Update set_wq_data() such that it sets the
  flags part to WORK_STRUCT_PENDING | WORK_STRUCT_STATIC if static |
  @extra_flags.

* Move santiy check on work->entry emptiness from queue_work_on() to
  __queue_work() which all queueing paths share.

* Make __queue_work() take @cpu and @wq instead of @cwq.

* Restructure flush_work() and __create_workqueue_key() to make them
  easier to modify.
Signed-off-by: NTejun Heo <tj@kernel.org>
      4690c4ab
    • T
      workqueue: kill RT workqueue · c790bce0
      由 Tejun Heo 提交于 
      With stop_machine() converted to use cpu_stop, RT workqueue doesn't
have any user left.  Kill RT workqueue support.
Signed-off-by: NTejun Heo <tj@kernel.org>
      c790bce0
  3. 16 11月, 2009 1 次提交
  5. 15 10月, 2009 2 次提交
  7. 21 9月, 2009 1 次提交
  9. 06 9月, 2009 1 次提交
  11. 03 4月, 2009 1 次提交
  13. 22 1月, 2009 1 次提交
  15. 12 1月, 2009 1 次提交
  17. 06 11月, 2008 1 次提交
    • R
      cpumask: introduce new API, without changing anything · 2d3854a3
      由 Rusty Russell 提交于 
      Impact: introduce new APIs

We want to deprecate cpumasks on the stack, as we are headed for
gynormous numbers of CPUs.  Eventually, we want to head towards an
undefined 'struct cpumask' so they can never be declared on stack.

1) New cpumask functions which take pointers instead of copies.
   (cpus_* -> cpumask_*)

2) Several new helpers to reduce requirements for temporary cpumasks
   (cpumask_first_and, cpumask_next_and, cpumask_any_and)

3) Helpers for declaring cpumasks on or offstack for large NR_CPUS
   (cpumask_var_t, alloc_cpumask_var and free_cpumask_var)

4) 'struct cpumask' for explicitness and to mark new-style code.

5) Make iterator functions stop at nr_cpu_ids (a runtime constant),
   not NR_CPUS for time efficiency and for smaller dynamic allocations
   in future.

6) cpumask_copy() so we can allocate less than a full cpumask eventually
   (for alloc_cpumask_var), and so we can eliminate the 'struct cpumask'
   definition eventually.

7) work_on_cpu() helper for doing task on a CPU, rather than saving old
   cpumask for current thread and manipulating it.

8) smp_call_function_many() which is smp_call_function_mask() except
   taking a cpumask pointer.

Note that this patch simply introduces the new functions and leaves
the obsolescent ones in place.  This is to simplify the transition
patches.
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      2d3854a3
  19. 22 10月, 2008 1 次提交
  21. 26 7月, 2008 1 次提交
    • O
      workqueues: implement flush_work() · db700897
      由 Oleg Nesterov 提交于 
      Most of users of flush_workqueue() can be changed to use cancel_work_sync(),
but sometimes we really need to wait for the completion and cancelling is not
an option. schedule_on_each_cpu() is good example.

Add the new helper, flush_work(work), which waits for the completion of the
specific work_struct. More precisely, it "flushes" the result of of the last
queue_work() which is visible to the caller.

For example, this code

	queue_work(wq, work);
	/* WINDOW */
	queue_work(wq, work);

	flush_work(work);

doesn't necessary work "as expected". What can happen in the WINDOW above is

	- wq starts the execution of work->func()

	- the caller migrates to another CPU

now, after the 2nd queue_work() this work is active on the previous CPU, and
at the same time it is queued on another. In this case flush_work(work) may
return before the first work->func() completes.

It is trivial to add another helper

	int flush_work_sync(struct work_struct *work)
	{
		return flush_work(work) || wait_on_work(work);
	}

which works "more correctly", but it has to iterate over all CPUs and thus
it much slower than flush_work().
Signed-off-by: NOleg Nesterov <oleg@tv-sign.ru>
Acked-by: NMax Krasnyansky <maxk@qualcomm.com>
Acked-by: NJarek Poplawski <jarkao2@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      db700897
  23. 25 7月, 2008 1 次提交
  25. 14 2月, 2008 1 次提交
  27. 16 1月, 2008 1 次提交
    • J
      lockdep: fix workqueue creation API lockdep interaction · eb13ba87
      由 Johannes Berg 提交于 
      Dave Young reported warnings from lockdep that the workqueue API
can sometimes try to register lockdep classes with the same key
but different names. This is not permitted in lockdep.

Unfortunately, I was unaware of that restriction when I wrote
the code to debug workqueue problems with lockdep and used the
workqueue name as the lockdep class name. This can obviously
lead to the problem if the workqueue name is dynamic.

This patch solves the problem by always using a constant name
for the workqueue's lockdep class, namely either the constant
name that was passed in or a string consisting of the variable
name.
Signed-off-by: NJohannes Berg <johannes@sipsolutions.net>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
      eb13ba87
  29. 20 10月, 2007 1 次提交
  31. 17 7月, 2007 2 次提交
  33. 18 5月, 2007 1 次提交
  35. 17 5月, 2007 1 次提交
  37. 10 5月, 2007 3 次提交