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2009-12-01SLOW_WORK: Move slow_work's proc file to debugfsDavid Howells
Move slow_work's debugging proc file to debugfs. Signed-off-by: David Howells <dhowells@redhat.com> Requested-and-acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-11-19SLOW_WORK: Allow a requeueable work item to sleep till the thread is neededDavid Howells
Add a function to allow a requeueable work item to sleep till the thread processing it is needed by the slow-work facility to perform other work. Sometimes a work item can't progress immediately, but must wait for the completion of another work item that's currently being processed by another slow-work thread. In some circumstances, the waiting item could instead - theoretically - put itself back on the queue and yield its thread back to the slow-work facility, thus waiting till it gets processing time again before attempting to progress. This would allow other work items processing time on that thread. However, this only works if there is something on the queue for it to queue behind - otherwise it will just get a thread again immediately, and will end up cycling between the queue and the thread, eating up valuable CPU time. So, slow_work_sleep_till_thread_needed() is provided such that an item can put itself on a wait queue that will wake it up when the event it is actually interested in occurs, then call this function in lieu of calling schedule(). This function will then sleep until either the item's event occurs or another work item appears on the queue. If another work item is queued, but the item's event hasn't occurred, then the work item should requeue itself and yield the thread back to the slow-work facility by returning. This can be used by CacheFiles for an object that is being created on one thread to wait for an object being deleted on another thread where there is nothing on the queue for the creation to go and wait behind. As soon as an item appears on the queue that could be given thread time instead, CacheFiles can stick the creating object back on the queue and return to the slow-work facility - assuming the object deletion didn't also complete. Signed-off-by: David Howells <dhowells@redhat.com>
2009-11-19SLOW_WORK: Allow the owner of a work item to determine if it is queued or notDavid Howells
Add a function (slow_work_is_queued()) to permit the owner of a work item to determine if the item is queued or not. The work item is counted as being queued if it is actually on the queue, not just if it is pending. If it is executing and pending, then it is not on the queue, but will rather be put back on the queue when execution finishes. This permits a caller to quickly work out if it may be able to put another, dependent work item on the queue behind it, or whether it will have to wait till that is finished. This can be used by CacheFiles to work out whether the creation a new object can be immediately deferred when it has to wait for an old object to be deleted, or whether a wait must take place. If a wait is necessary, then the slow-work thread can otherwise get blocked, preventing the deletion from taking place. Signed-off-by: David Howells <dhowells@redhat.com>
2009-11-19SLOW_WORK: Allow the work items to be viewed through a /proc fileDavid Howells
Allow the executing and queued work items to be viewed through a /proc file for debugging purposes. The contents look something like the following: THR PID ITEM ADDR FL MARK DESC === ===== ================ == ===== ========== 0 3005 ffff880023f52348 a 952ms FSC: OBJ17d3: LOOK 1 3006 ffff880024e33668 2 160ms FSC: OBJ17e5 OP60d3b: Write1/Store fl=2 2 3165 ffff8800296dd180 a 424ms FSC: OBJ17e4: LOOK 3 4089 ffff8800262c8d78 a 212ms FSC: OBJ17ea: CRTN 4 4090 ffff88002792bed8 2 388ms FSC: OBJ17e8 OP60d36: Write1/Store fl=2 5 4092 ffff88002a0ef308 2 388ms FSC: OBJ17e7 OP60d2e: Write1/Store fl=2 6 4094 ffff88002abaf4b8 2 132ms FSC: OBJ17e2 OP60d4e: Write1/Store fl=2 7 4095 ffff88002bb188e0 a 388ms FSC: OBJ17e9: CRTN vsq - ffff880023d99668 1 308ms FSC: OBJ17e0 OP60f91: Write1/EnQ fl=2 vsq - ffff8800295d1740 1 212ms FSC: OBJ16be OP4d4b6: Write1/EnQ fl=2 vsq - ffff880025ba3308 1 160ms FSC: OBJ179a OP58dec: Write1/EnQ fl=2 vsq - ffff880024ec83e0 1 160ms FSC: OBJ17ae OP599f2: Write1/EnQ fl=2 vsq - ffff880026618e00 1 160ms FSC: OBJ17e6 OP60d33: Write1/EnQ fl=2 vsq - ffff880025a2a4b8 1 132ms FSC: OBJ16a2 OP4d583: Write1/EnQ fl=2 vsq - ffff880023cbe6d8 9 212ms FSC: OBJ17eb: LOOK vsq - ffff880024d37590 9 212ms FSC: OBJ17ec: LOOK vsq - ffff880027746cb0 9 212ms FSC: OBJ17ed: LOOK vsq - ffff880024d37ae8 9 212ms FSC: OBJ17ee: LOOK vsq - ffff880024d37cb0 9 212ms FSC: OBJ17ef: LOOK vsq - ffff880025036550 9 212ms FSC: OBJ17f0: LOOK vsq - ffff8800250368e0 9 212ms FSC: OBJ17f1: LOOK vsq - ffff880025036aa8 9 212ms FSC: OBJ17f2: LOOK In the 'THR' column, executing items show the thread they're occupying and queued threads indicate which queue they're on. 'PID' shows the process ID of a slow-work thread that's executing something. 'FL' shows the work item flags. 'MARK' indicates how long since an item was queued or began executing. Lastly, the 'DESC' column permits the owner of an item to give some information. Signed-off-by: David Howells <dhowells@redhat.com>
2009-11-19SLOW_WORK: Add delayed_slow_work supportJens Axboe
This adds support for starting slow work with a delay, similar to the functionality we have for workqueues. Signed-off-by: Jens Axboe <jens.axboe@oracle.com> Signed-off-by: David Howells <dhowells@redhat.com>
2009-11-19SLOW_WORK: Add support for cancellation of slow workJens Axboe
Add support for cancellation of queued slow work and delayed slow work items. The cancellation functions will wait for items that are pending or undergoing execution to be discarded by the slow work facility. Attempting to enqueue work that is in the process of being cancelled will result in ECANCELED. Signed-off-by: Jens Axboe <jens.axboe@oracle.com> Signed-off-by: David Howells <dhowells@redhat.com>
2009-11-19SLOW_WORK: Make slow_work_ops ->get_ref/->put_ref optionalJens Axboe
Make the ability for the slow-work facility to take references on a work item optional as not everyone requires this. Even the internal slow-work stubs them out, so those can be got rid of too. Signed-off-by: Jens Axboe <jens.axboe@oracle.com> Signed-off-by: David Howells <dhowells@redhat.com>
2009-11-19SLOW_WORK: Wait for outstanding work items belonging to a module to clearDavid Howells
Wait for outstanding slow work items belonging to a module to clear when unregistering that module as a user of the facility. This prevents the put_ref code of a work item from being taken away before it returns. Signed-off-by: David Howells <dhowells@redhat.com>
2009-04-03Document the slow work thread poolDavid Howells
Document the slow work thread pool. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Steve Dickson <steved@redhat.com> Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com> Acked-by: Al Viro <viro@zeniv.linux.org.uk> Tested-by: Daire Byrne <Daire.Byrne@framestore.com>