SDIO Performance once again

[David Anders]

Dan,

i can give it a try on my s3c2440 platform later this week to see if it improves performance.


thanks
Dave Anders
AML


--- On Wed, 2/18/09, Dan Williams <dcbw at redhat.com> wrote:

> From: Dan Williams <dcbw at redhat.com>
> Subject: Re: SDIO Performance once again
> To: "Cliff Cai" <cliffcai.sh at gmail.com>
> Cc: lists at dsh-elektronik.de, "Robin Getz" <rgetz at blackfin.uclinux.org>, libertas-dev at lists.infradead.org
> Date: Wednesday, February 18, 2009, 1:24 PM
> 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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> > > libertas-dev at lists.infradead.org
> > >
> http://lists.infradead.org/mailman/listinfo/libertas-dev
> > >
> > 
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