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  1. Jun 29, 2010
    • Tejun Heo's avatar
      workqueue: reimplement workqueue freeze using max_active · a0a1a5fd
      Tejun Heo authored 
      

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: default avatarTejun Heo <tj@kernel.org>
      a0a1a5fd
    • Tejun Heo's avatar
      workqueue: implement per-cwq active work limit · 1e19ffc6
      Tejun Heo authored 
      

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: default avatarTejun Heo <tj@kernel.org>
      1e19ffc6
    • Tejun Heo's avatar
      workqueue: reimplement work flushing using linked works · affee4b2
      Tejun Heo authored 
      

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: default avatarTejun Heo <tj@kernel.org>
      affee4b2
    • Tejun Heo's avatar
      workqueue: introduce worker · c34056a3
      Tejun Heo authored 
      

Separate out worker thread related information to struct worker from
struct cpu_workqueue_struct and implement helper functions to deal
with the new struct worker.  The only change which is visible outside
is that now workqueue worker are all named "kworker/CPUID:WORKERID"
where WORKERID is allocated from per-cpu ida.

This is in preparation of concurrency managed workqueue where shared
multiple workers would be available per cpu.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
      c34056a3
    • Tejun Heo's avatar
      workqueue: reimplement workqueue flushing using color coded works · 73f53c4a
      Tejun Heo authored 
      

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: default avatarTejun Heo <tj@kernel.org>
      73f53c4a
    • Tejun Heo's avatar
      workqueue: update cwq alignement · 0f900049
      Tejun Heo authored 
      

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: default avatarTejun 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: default avatarMichal Simek <michal.simek@petalogix.com>
      0f900049
    • Tejun Heo's avatar
      workqueue: kill cpu_populated_map · 1537663f
      Tejun Heo authored 
      

Worker management is about to be overhauled.  Simplify things by
removing cpu_populated_map, creating workers for all possible cpus and
making single threaded workqueues behave more like multi threaded
ones.

After this patch, all cwqs are always initialized, all workqueues are
linked on the workqueues list and workers for all possibles cpus
always exist.  This also makes CPU hotplug support simpler - checking
->cpus_allowed before processing works in worker_thread() and flushing
cwqs on CPU_POST_DEAD are enough.

While at it, make get_cwq() always return the cwq for the specified
cpu, add target_cwq() for cases where single thread distinction is
necessary and drop all direct usage of per_cpu_ptr() on wq->cpu_wq.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
      1537663f
    • Tejun Heo's avatar
      workqueue: temporarily remove workqueue tracing · 64166699
      Tejun Heo authored 
      

Strip tracing code from workqueue and remove workqueue tracing.  This
is temporary measure till concurrency managed workqueue is complete.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
      64166699
    • Tejun Heo's avatar
      workqueue: separate out process_one_work() · a62428c0
      Tejun Heo authored 
      

Separate out process_one_work() out of run_workqueue().  This patch
doesn't cause any behavior change.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
      a62428c0
    • Tejun Heo's avatar
      workqueue: define masks for work flags and conditionalize STATIC flags · 22df02bb
      Tejun Heo authored 
      

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: default avatarTejun Heo <tj@kernel.org>
      22df02bb
    • Tejun Heo's avatar
      workqueue: merge feature parameters into flags · 97e37d7b
      Tejun Heo authored 
      

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: default avatarTejun Heo <tj@kernel.org>
      97e37d7b
    • Tejun Heo's avatar
      workqueue: misc/cosmetic updates · 4690c4ab
      Tejun Heo authored 
      

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: default avatarTejun Heo <tj@kernel.org>
      4690c4ab
    • Tejun Heo's avatar
      workqueue: kill RT workqueue · c790bce0
      Tejun Heo authored 
      

With stop_machine() converted to use cpu_stop, RT workqueue doesn't
have any user left.  Kill RT workqueue support.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
      c790bce0
    • Tejun Heo's avatar
      acpi: use queue_work_on() instead of binding workqueue worker to cpu0 · 8fec62b2
      Tejun Heo authored 
      

ACPI works need to be executed on cpu0 and acpi/osl.c achieves this by
creating singlethread workqueue and then binding it to cpu0 from a
work which is quite unorthodox.  Make it create regular workqueues and
use queue_work_on() instead.  This is in preparation of concurrency
managed workqueue and the extra workers won't be a problem after it's
implemented.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
      8fec62b2
    • Tejun Heo's avatar
      kthread: implement kthread_data() · 82805ab7
      Tejun Heo authored 
      

Implement kthread_data() which takes @task pointing to a kthread and
returns @data specified when creating the kthread.  The caller is
responsible for ensuring the validity of @task when calling this
function.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
      82805ab7
    • Tejun Heo's avatar
      ivtv: use kthread_worker instead of workqueue · 7bc46560
      Tejun Heo authored 
      

Upcoming workqueue updates will no longer guarantee fixed workqueue to
worker kthread association, so giving RT priority to the irq worker
won't work.  Use kthread_worker which guarantees specific kthread
association instead.  This also makes setting the priority cleaner.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Andy Walls <awalls@md.metrocast.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: ivtv-devel@ivtvdriver.org
Cc: linux-media@vger.kernel.org
      7bc46560
    • Tejun Heo's avatar
      kthread: implement kthread_worker · b56c0d89
      Tejun Heo authored 
      

Implement simple work processor for kthread.  This is to ease using
kthread.  Single thread workqueue used to be used for things like this
but workqueue won't guarantee fixed kthread association anymore to
enable worker sharing.

This can be used in cases where specific kthread association is
necessary, for example, when it should have RT priority or be assigned
to certain cgroup.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
      b56c0d89
  3. Jun 14, 2010
  5. Jun 12, 2010