SDIO Performance once again

[Dan Williams]

On Wed, 2009-02-11 at 11:36 +0800, Cliff Cai wrote:
> I think this is caused by the mechanism to start a transfer from host to card.
> see if_sdio_host_to_card() in if_sdio.c,it uses schedule_work to call
> if_sdio_host_to_card_worker()
> which start the transfer.

I spent a bit of time trying to figure out why if_sdio was written this
way.  Couldn't find it.  ISTR having specific conversations with Pierre
about using a worker thread to send data from host -> card, it might
have had to do with locking or interrupt issues.

One method to reduce latency is to move the worker thread into its own
workqueue.  It's currently on the generic workqueue, which could be
waiting for other stuff.  So creating a private workqueue and using
queue_work() to kick off the send might do the trick.

Anyone want to try the attached patch and see if it makes life better?
Compile-tested, but not run tested.

Dan

> Cliff
> 
> On Wed, Feb 11, 2009 at 4:44 AM, Dominik S. Herwald
> <lists at dsh-elektronik.de> wrote:
> > Robin Getz schrieb:
> >> On Mon 9 Feb 2009 08:09, Dominik S. Herwald pondered:
> >>
> >>> In the meantime I found out that my Problem seems to be related to the
> >>> Kernel timer tick of 4ms
> >>> (see my second posting on this list with the 4ms frames)...
> >>> On Blackfin the Timer tick is set to 250Hz (4ms) by default. If I set it
> >>>
> >>> to 1000Hz,
> >>> performance rises up to 11.2MBit/s performance!
> >>>
> >>
> >> What happens when you select tickless?
> >>
> >> Select GENERIC_TIME && GENERIC_CLOCKEVENTS && CYCLES_CLOCKSOURCE
> >>
> >> And it should show up as "Tickless System (Dynamic Ticks)".
> >>
> >> -Robin
> >>
> >>
> >
> > It performs the same (11MBit/s) as with 1000Hz Timer tick.
> > On the Scope I can see a 1ms transfer interval instead of 4ms.
> > There is still plenty of room in between the transfers on the SDIO Bus...
> >
> > If I set the Clock to 250Hz while these tickless options are active, the 4ms
> > Interval is there again.
> >
> >
> > I had a closer look at the Libertas Code - nearly everywhere in Libertas
> > the Kernel Tick
> > is only used for timeouts in the range of seconds. I did not see
> > anything that could
> > affect the transfer.  But I am really no Kernel Driver expert so I may
> > have overlooked
> > something...
> >
> > Best regards,
> > Dominik
> >
> >
> >
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> >
> 
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