Messages in this thread |  | | | Date | Thu, 17 May 2012 08:06:49 -0700 | | From | Tejun Heo <> | | Subject | Re: [PATCH] floppy: convert to delayed work and single-thread wq |
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On Wed, May 16, 2012 at 10:44:31PM +0200, Jiri Kosina wrote: > On Wed, 16 May 2012, Tejun Heo wrote: > > > > In floppy_grab_irq_and_dma() the point is to drain the workqueue > > > completely (before the conversion, we were just using > > > flush_work_sync(&floppy_work) for particular work item), and for that > > > flush_work() is not sufficient any more. > > > > > > So I am really considering going back to driver-specific singlethreaded > > > workqueue. > > > > Ummm... still confused. flush_work_sync() is fine too. If you have > > two, two calls to flush_work_sync() are equivalent to flushing the > > workqueue in effect. You just need to avoid flush_workqueue() because > > system workqueues may be hosting work items which can run arbitrarily > > long. > > Before the conversion, we do > > flush_work_sync(&floppy_work); > > in floppy_grab_irq_and_dma(). After the conversion, the single-threaded > workqueue is used to queue more than just floppy_work, and we want all > this to be flushed before proceeding, so neither flush_work() nor > flush_work_sync() is enough, as there might be floppy_work, fd_timer or > fd_timeout queued. This all has to be flushed. > > If this still doesn't seem to make sense, I'll get back to it tomorrow, it > might be just too late and my brain cells might already be dreaming.
So, AFAICS, there are only three work items in question here, floppy_work, fd_timer and fd_timeout, so three calls to flush[_delayed]_work_sync() is functionally equivalent to flush_workqueue(). While flushing separately may take longer, AFAICS, it doesn't seem to be on the hot path (not much in floppy can be considered hot these days tho) and I don't think it would make any noticeable performance difference.
If having a separate flush domain is beneficial, please create a non-reentrant workqueue without rescuer - alloc_workqueue("floppy", WQ_NON_REENTRANT, 0). If serialization among different work items is necessary, single thread workqueue without rescuer can be used - alloc_workqueue("floppy", WQ_UNBOUND, 1).
create_*workqueue() are left there for backwards compatibility and they all have rescuer for that reason. Gotta clean them up and maybe create different wrappers, I guess.
Thanks.
-- tejun
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