From: Greg KH <greg@kroah.com>
To: Vitaly Wool <vwool@ru.mvista.com>
Cc: David Brownell <david-b@pacbell.net>,
linux-kernel@vger.kernel.org, dpervushin@gmail.com,
akpm@osdl.org, basicmark@yahoo.com, komal_shah802003@yahoo.com,
stephen@streetfiresound.com,
spi-devel-general@lists.sourceforge.net, Joachim_Jaeger@digi.com
Subject: Re: [PATCH/RFC] SPI: add DMAUNSAFE analog to David Brownell's core
Date: Wed, 14 Dec 2005 09:18:42 -0800 [thread overview]
Message-ID: <20051214171842.GB30546@kroah.com> (raw)
In-Reply-To: <43A0230B.1040904@ru.mvista.com>
On Wed, Dec 14, 2005 at 04:50:03PM +0300, Vitaly Wool wrote:
> Greg KH wrote:
>
> >On Tue, Dec 13, 2005 at 11:01:01AM -0800, David Brownell wrote:
> >
> >
> >>It's way better to just insist that all I/O buffers (in all
> >>generic APIs) be DMA-safe. AFAICT that's a pretty standard
> >>rule everywhere in Linux.
> >>
> >>
> >
> >I agree.
> >
> >
> Well, why then David doesn't insist on that in his own code?
Heh, I don't know, only David can answer that :)
> His synchronous transfer functions are allocating transfer buffers on
> stack which is not DMA-safe.
> Then he starts messing with allocate-or-use-preallocated stuff etc. etc.
> Why isn't he just kmalloc'ing/kfree'ing buffers each time these
> functions are called (as he proposes for upper layer drivers to do)?
> That's a significant inconsistency. Is it also the thing you agree with?
>
> And they way he does it implies redundant memcpy's and kmalloc's:
> suppose we have two controller drivers working in two threads and
> calling write_then_read in such a way that the one called later has to
> allocate a new buffer. Suppose also that both controller drivers are
> working in *PIO* mode. In this situation you have one redundant kmalloc
> and two redundant memcpy's, not speaking about overhead brought up by
> mutexes.
>
> The thing is that only controller driver is aware whether DMA is
> needed or not, so it's controller driver that should work it out.
> Requesting all the buffers to be DMA-safe will make a significant
> performance drop on all small transfers!
What is the speed of your SPI bus?
And what are your preformance requirements?
thanks,
greg k-h
next prev parent reply other threads:[~2005-12-14 17:24 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-12-12 15:20 [PATCH 2.6-git 0/4] SPI core refresh Vitaly Wool
2005-12-12 15:22 ` [PATCH 2.6-git 1/4] SPI core refresh: SPI core patch Vitaly Wool
2005-12-12 15:49 ` Russell King
2005-12-12 15:24 ` [PATCH 2.6-git 2/4] SPI core refresh: MTD dataflash driver Vitaly Wool
2005-12-12 15:26 ` [PATCH 2.6-git 3/4] SPI core refresh: SPI/PNX controller Vitaly Wool
2005-12-12 15:27 ` [PATCH 2.6-git 4/4] SPI core refresh: dumb EEPROM driver Vitaly Wool
2005-12-12 18:01 ` [PATCH 2.6-git 0/4] SPI core refresh Rui Sousa
2005-12-13 12:09 ` [spi-devel-general] " dmitry pervushin
2005-12-13 15:11 ` Rui Sousa
2005-12-13 17:06 ` dmitry pervushin
2005-12-14 6:57 ` Vitaly Wool
2005-12-14 14:28 ` Rui Sousa
2005-12-13 16:35 ` David Brownell
2005-12-13 18:02 ` Rui Sousa
2005-12-13 14:06 ` [PATCH/RFC] SPI: add async message handing library to David Brownell's core Vitaly Wool
2005-12-13 16:53 ` [PATCH/RFC] SPI: add DMAUNSAFE analog " Vitaly Wool
2005-12-13 19:01 ` David Brownell
2005-12-13 19:15 ` Greg KH
2005-12-14 13:50 ` Vitaly Wool
2005-12-14 17:18 ` Greg KH [this message]
2005-12-14 17:53 ` Vitaly Wool
2005-12-14 18:50 ` [PATCH/RFC] SPI: add DMAUNSAFE analog David Brownell
2005-12-14 19:29 ` Vitaly Wool
2005-12-14 19:02 ` [PATCH/RFC] SPI: add DMAUNSAFE analog to David Brownell's core David Brownell
2005-12-14 19:19 ` Vitaly Wool
2005-12-14 19:33 ` [spi-devel-general] Re: [PATCH/RFC] SPI: add DMAUNSAFE analog David Brownell
2005-12-14 19:34 ` [PATCH/RFC] SPI: add DMAUNSAFE analog to David Brownell's core Vitaly Wool
2005-12-15 6:47 ` Vitaly Wool
2005-12-15 16:44 ` Greg KH
2005-12-15 22:23 ` Vitaly Wool
2005-12-15 23:02 ` Greg KH
2005-12-16 8:37 ` Vitaly Wool
2005-12-16 17:34 ` Greg KH
2005-12-16 18:32 ` [spi-devel-general] Re: [PATCH/RFC] SPI: add DMAUNSAFE analog David Brownell
2005-12-15 20:06 ` David Brownell
2005-12-15 22:17 ` Vitaly Wool
2005-12-15 22:33 ` Greg KH
2005-12-16 3:34 ` Andy Isaacson
2005-12-16 5:17 ` Greg KH
2005-12-14 19:16 ` [PATCH/RFC] SPI: add DMAUNSAFE analog to David Brownell's core Greg KH
2005-12-14 19:30 ` Vitaly Wool
2005-12-15 10:00 ` [spi-devel-general] " dmitry pervushin
2005-12-14 17:22 ` David Brownell
2005-12-14 17:50 ` Vitaly Wool
2005-12-14 19:17 ` [PATCH/RFC] SPI: add DMAUNSAFE analog David Brownell
2005-12-14 20:11 ` Vitaly Wool
2005-12-13 21:47 ` [PATCH/RFC] SPI: add DMAUNSAFE analog to David Brownell's core Vitaly Wool
2005-12-13 22:15 ` Vitaly Wool
2005-12-14 16:55 ` David Brownell
2005-12-14 17:23 ` Vitaly Wool
2005-12-14 18:48 ` [PATCH/RFC] SPI: add async message handing library " Stephen Street
2005-12-14 19:41 ` Vitaly Wool
2005-12-14 21:19 ` Stephen Street
2005-12-14 19:31 ` [PATCH/RFC] SPI: add async message handing library David Brownell
2005-12-15 12:19 ` [PATCH/RFC] SPI: async message handing library update Vitaly Wool
2005-12-18 18:59 ` David Brownell
2005-12-19 15:40 ` [spi-devel-general] " dmitry pervushin
2005-12-20 7:23 ` David Brownell
2005-12-20 18:02 ` Vitaly Wool
2005-12-22 17:28 ` David Brownell
2005-12-22 22:10 ` Vitaly Wool
2005-12-22 23:55 ` David Brownell
2005-12-21 13:17 ` Vitaly Wool
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