Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [PATCH] firmware_class: Move request_firmware_nowait() to workqueues | Date | Fri, 16 Mar 2012 22:45:52 +0100 |
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On Friday, March 16, 2012, Stephen Boyd wrote: > On 03/16/12 13:19, Rafael J. Wysocki wrote: > > On Friday, March 16, 2012, Stephen Boyd wrote: > >> On 03/15/12 15:31, Rafael J. Wysocki wrote: > >>> On Thursday, March 15, 2012, Stephen Boyd wrote: > >>>> On 03/15/12 13:07, Christian Lamparter wrote: > >>>>> On Thursday, March 15, 2012 08:50:15 PM Stephen Boyd wrote: > >>>>>> Oddly enough a work_struct was already part of the firmware_work > >>>>>> structure but nobody was using it. Instead of creating a new > >>>>>> kthread for each request_firmware_nowait() just schedule the work > >>>>>> on the system workqueue. This should avoid some overhead in > >>>>>> forking new threads when they're not strictly necessary if > >>>>>> workqueues are available. > >>>>>> > >>>>>> Signed-off-by: Stephen Boyd <sboyd@codeaurora.org> > >>>>>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > >>>>>> Cc: Kay Sievers <kay.sievers@vrfy.org> > >>>>>> Cc: Rafael J. Wysocki <rjw@sisk.pl> > >>>>>> --- > >>>>>> > >>>>>> I saw this while looking at this problem we're having. > >>>>> Correct me if I'm wrong, but wouldn't that stall all other > >>>>> global workqueue tasks for up to 60 seconds [in worst case]? > >>>>> > >>>>> But I think we can get rid of the firmware_work work struct... > >>>>> > >>>> My understanding is that with concurrency managed workqueues when the > >>>> work item blocks another will be scheduled to run almost immediately. So > >>>> before that change by Tejun workqueues would have been a bad idea > >>>> because it could have blocked up to 60 second but now it should be fine > >>>> because that work item will just be put to sleep and another request > >>>> will run. > >>> Please read the description of system_wq in workqueue.h. > >>> > >>> You should have used either system_long_wq or system_nrt_wq (depending on > >>> what you really need). > >>> > >>> > >> Thanks. I think we can use system_nrt_wq then? Or maybe even the > >> unbounded workqueue system_unbound_wq? > > Hmm. Can you please remind me what the exact role of that work item is? > > > > It loads the device's firmware, but I'm not sure in what situations that's > > supposed to happen. > > > > request_firmware_nowait() is used by code that wants to get the firmware > asynchronously. Callers pass in a callback function which is called once > the firmware is retrieved. The work item will correspond to one call to > request_firmware_nowait(), where the work item will handle the sysfs > entry generation, uevent generation, and wait_for_completion() calls > that _request_firmware() does. > > The work item also executes the callback function the caller passes in > which could do probably anything and could take an arbitrarily long > time. It looks like some drivers even chain request_firmware_nowait() > together by calling request_firmware_nowait() from the callback functions.
So it looks like an unbound workqueue would be suitable for that, but perhaps it may even be an ordered one?
Rafael
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