From: Mike Frysinger <vapier.adi@gmail.com>
To: Johannes Weiner <jw@emlix.com>
Cc: "Oskar Schirmer" <os@emlix.com>,
"Dmitry Torokhov" <dmitry.torokhov@gmail.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
linux-input@vger.kernel.org, linux-kernel@vger.kernel.org,
"Daniel Glöckner" <dg@emlix.com>,
"Oliver Schneidewind" <osw@emlix.com>
Subject: Re: [PATCH] ad7877: keep dma rx buffers in seperate cache lines
Date: Sun, 9 May 2010 00:45:41 -0400 [thread overview]
Message-ID: <l2u8bd0f97a1005082145te5965291q91a5daa01695e3d9@mail.gmail.com> (raw)
In-Reply-To: <20100508223206.GA365@emlix.com>
On Sat, May 8, 2010 at 18:32, Johannes Weiner wrote:
> On Fri, May 07, 2010 at 02:28:16PM -0400, Mike Frysinger wrote:
>> On Fri, May 7, 2010 at 06:15, Oskar Schirmer wrote:
>> > On Thu, May 06, 2010 at 14:46:04 -0400, Mike Frysinger wrote:
>> >> On Thu, May 6, 2010 at 06:37, Oskar Schirmer wrote:
>> >> > struct ser_req {
>> >> > + u16 sample;
>> >> > + char __padalign[L1_CACHE_BYTES - sizeof(u16)];
>> >> > +
>> >> > u16 reset;
>> >> > u16 ref_on;
>> >> > u16 command;
>> >> > - u16 sample;
>> >> > struct spi_message msg;
>> >> > struct spi_transfer xfer[6];
>> >> > };
>> >>
>> >> are you sure this is necessary ? ser_req is only ever used with
>> >> spi_sync() and it's allocated/released on the fly, so how could
>> >> anything be reading that memory between the start of the transmission
>> >> and the return to adi7877 ?
>> >
>> > msg is handed over to spi_sync, it contains the addresses
>> > which will be used to programme the DMA: the spi master
>> > transfer function will read these fields to start DMA.
>>
>> so the issue is coming from the SPI master drivers and not the AD7877 driver
>
> No, the issue is coming from ad7877 placing a transmission buffer
> into the same cache line with memory locations that are accessed outside
> the driver's scope.
you missed the point of my comment. as i clearly explained in the
other structure, the AD7877 driver was causing the cache desync. here
it is the SPI master that is implicitly causing it. i'm not talking
about the AD7877 being correct wrt to the implicit SPI/DMA
requirements, just what code exactly is triggering the cache issues.
> /*
> * DMA (thus cache coherency maintainance) requires the
> * transfer buffers to live in their own cache lines.
> */
> char __padalign[...];
>
> ? It might be obvious what the code does, but I agree with
> Mike that it might not be immediately apparent why it's needed.
comment looks fine once the spelling is fixed (maintenance). thanks.
-mike
WARNING: multiple messages have this Message-ID (diff)
From: Mike Frysinger <vapier.adi@gmail.com>
To: Johannes Weiner <jw@emlix.com>
Cc: "Oskar Schirmer" <os@emlix.com>,
"Dmitry Torokhov" <dmitry.torokhov@gmail.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
linux-input@vger.kernel.org, linux-kernel@vger.kernel.org,
"Daniel Glöckner" <dg@emlix.com>,
"Oliver Schneidewind" <osw@emlix.com>
Subject: Re: [PATCH] ad7877: keep dma rx buffers in seperate cache lines
Date: Sun, 9 May 2010 00:45:41 -0400 [thread overview]
Message-ID: <l2u8bd0f97a1005082145te5965291q91a5daa01695e3d9@mail.gmail.com> (raw)
In-Reply-To: <20100508223206.GA365@emlix.com>
On Sat, May 8, 2010 at 18:32, Johannes Weiner wrote:
> On Fri, May 07, 2010 at 02:28:16PM -0400, Mike Frysinger wrote:
>> On Fri, May 7, 2010 at 06:15, Oskar Schirmer wrote:
>> > On Thu, May 06, 2010 at 14:46:04 -0400, Mike Frysinger wrote:
>> >> On Thu, May 6, 2010 at 06:37, Oskar Schirmer wrote:
>> >> > struct ser_req {
>> >> > + u16 sample;
>> >> > + char __padalign[L1_CACHE_BYTES - sizeof(u16)];
>> >> > +
>> >> > u16 reset;
>> >> > u16 ref_on;
>> >> > u16 command;
>> >> > - u16 sample;
>> >> > struct spi_message msg;
>> >> > struct spi_transfer xfer[6];
>> >> > };
>> >>
>> >> are you sure this is necessary ? ser_req is only ever used with
>> >> spi_sync() and it's allocated/released on the fly, so how could
>> >> anything be reading that memory between the start of the transmission
>> >> and the return to adi7877 ?
>> >
>> > msg is handed over to spi_sync, it contains the addresses
>> > which will be used to programme the DMA: the spi master
>> > transfer function will read these fields to start DMA.
>>
>> so the issue is coming from the SPI master drivers and not the AD7877 driver
>
> No, the issue is coming from ad7877 placing a transmission buffer
> into the same cache line with memory locations that are accessed outside
> the driver's scope.
you missed the point of my comment. as i clearly explained in the
other structure, the AD7877 driver was causing the cache desync. here
it is the SPI master that is implicitly causing it. i'm not talking
about the AD7877 being correct wrt to the implicit SPI/DMA
requirements, just what code exactly is triggering the cache issues.
> /*
> * DMA (thus cache coherency maintainance) requires the
> * transfer buffers to live in their own cache lines.
> */
> char __padalign[...];
>
> ? It might be obvious what the code does, but I agree with
> Mike that it might not be immediately apparent why it's needed.
comment looks fine once the spelling is fixed (maintenance). thanks.
-mike
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next prev parent reply other threads:[~2010-05-09 4:46 UTC|newest]
Thread overview: 124+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-05-06 10:37 [PATCH] ad7877: fix spi word size to 16 bit Oskar Schirmer
2010-05-06 10:37 ` Oskar Schirmer
2010-05-06 10:37 ` [PATCH] ad7877: keep dma rx buffers in seperate cache lines Oskar Schirmer
2010-05-06 18:46 ` Mike Frysinger
2010-05-06 18:46 ` Mike Frysinger
2010-05-07 10:15 ` Oskar Schirmer
2010-05-07 10:15 ` Oskar Schirmer
2010-05-07 18:28 ` Mike Frysinger
2010-05-07 18:28 ` Mike Frysinger
2010-05-08 22:32 ` Johannes Weiner
2010-05-08 22:32 ` Johannes Weiner
2010-05-09 4:45 ` Mike Frysinger [this message]
2010-05-09 4:45 ` Mike Frysinger
2010-05-09 8:50 ` Oskar Schirmer
2010-05-09 8:50 ` Oskar Schirmer
2010-05-07 12:07 ` Johannes Weiner
2010-05-10 10:34 ` [PATCH v2] " Oskar Schirmer
2010-05-10 10:34 ` Oskar Schirmer
2010-05-10 10:42 ` [PATCH v3] " Oskar Schirmer
2010-05-10 10:42 ` Oskar Schirmer
2010-05-10 16:39 ` Mike Frysinger
2010-05-10 20:54 ` Dmitry Torokhov
2010-05-10 21:22 ` Andrew Morton
2010-05-10 21:27 ` Mike Frysinger
2010-05-11 6:05 ` Dmitry Torokhov
2010-05-11 6:05 ` Dmitry Torokhov
2010-05-11 6:11 ` Mike Frysinger
2010-05-11 6:11 ` Mike Frysinger
2010-05-11 3:20 ` Andrew Morton
2010-05-11 6:21 ` Dmitry Torokhov
2010-05-11 6:23 ` Mike Frysinger
2010-05-11 6:23 ` Mike Frysinger
2010-05-11 6:33 ` Dmitry Torokhov
2010-05-11 6:33 ` Dmitry Torokhov
2010-05-11 6:37 ` Mike Frysinger
2010-05-11 6:42 ` Pekka Enberg
2010-05-11 13:57 ` Christoph Lameter
2010-05-11 16:52 ` Dmitry Torokhov
2010-05-11 17:31 ` Mike Frysinger
2010-05-11 18:59 ` Pekka Enberg
2010-05-11 20:03 ` Mike Frysinger
2010-05-11 20:07 ` Matt Mackall
2010-05-11 20:10 ` Mike Frysinger
2010-05-11 20:10 ` Mike Frysinger
2010-05-11 20:21 ` Christoph Lameter
2010-05-11 20:34 ` Mike Frysinger
2010-05-11 20:38 ` Pekka Enberg
2010-05-11 20:43 ` Mike Frysinger
2010-05-11 20:43 ` Mike Frysinger
2010-05-11 20:47 ` Pekka Enberg
2010-05-13 6:21 ` Paul Mundt
2010-05-11 20:46 ` Christoph Lameter
2010-05-11 20:54 ` Mike Frysinger
2010-05-11 20:54 ` Mike Frysinger
2010-05-11 21:01 ` Pekka Enberg
2010-05-11 21:11 ` Mike Frysinger
2010-05-11 21:11 ` Mike Frysinger
2010-05-12 1:58 ` FUJITA Tomonori
[not found] ` <20100511214836.GH1726@emlix.com>
2010-05-11 21:53 ` Dmitry Torokhov
2010-05-11 22:39 ` Mike Frysinger
2010-05-11 22:39 ` Mike Frysinger
2010-05-12 2:07 ` [LKML] " Marc Gauthier
2010-05-12 3:03 ` Nick Piggin
2010-05-12 3:23 ` FUJITA Tomonori
2010-05-12 4:35 ` Mike Frysinger
2010-05-12 4:35 ` Mike Frysinger
2010-05-12 5:28 ` FUJITA Tomonori
2010-05-12 5:28 ` FUJITA Tomonori
2010-05-12 14:37 ` Mike Frysinger
2010-05-12 14:37 ` Mike Frysinger
2010-05-12 18:11 ` Dmitry Torokhov
2010-05-12 18:28 ` Mike Frysinger
2010-05-12 18:28 ` Mike Frysinger
2010-05-12 10:36 ` Johannes Weiner
2010-05-12 12:35 ` Marc Gauthier
2010-05-12 14:36 ` Mike Frysinger
2010-05-12 14:36 ` Mike Frysinger
2010-05-19 12:48 ` David Woodhouse
2010-05-19 13:07 ` Nick Piggin
2010-05-19 13:17 ` David Woodhouse
2010-05-19 13:36 ` Nick Piggin
2010-05-19 13:44 ` Johannes Weiner
2010-05-19 13:52 ` Nick Piggin
2010-05-19 14:38 ` FUJITA Tomonori
2010-05-19 14:58 ` David Woodhouse
2010-05-20 4:42 ` FUJITA Tomonori
2010-05-19 16:37 ` Dmitry Torokhov
2010-05-19 15:00 ` Johannes Weiner
2010-05-17 6:12 ` Michal Simek
2010-05-19 13:00 ` David Woodhouse
2010-05-11 22:37 ` Alan Cox
2010-05-11 20:22 ` Pekka Enberg
2010-05-11 14:12 ` Oskar Schirmer
2010-05-11 14:12 ` Oskar Schirmer
2010-05-06 11:18 ` [PATCH] ad7877: fix spi word size to 16 bit Hennerich, Michael
2010-05-06 11:18 ` Hennerich, Michael
2010-05-06 18:26 ` Mike Frysinger
2010-05-06 18:26 ` Mike Frysinger
2010-05-07 9:41 ` Daniel Glöckner
2010-05-07 9:41 ` Daniel Glöckner
2010-05-07 18:23 ` Mike Frysinger
2010-05-07 18:23 ` Mike Frysinger
2010-05-13 7:53 ` Dmitry Torokhov
2010-05-13 7:53 ` Dmitry Torokhov
2010-05-15 18:15 ` Oskar Schirmer
2010-05-15 18:15 ` Oskar Schirmer
2010-05-16 19:25 ` Mike Frysinger
2010-05-16 19:25 ` Mike Frysinger
2010-05-17 7:29 ` Oskar Schirmer
2010-05-17 7:29 ` Oskar Schirmer
2010-05-17 8:14 ` Hennerich, Michael
2010-05-17 8:14 ` Hennerich, Michael
2010-05-17 8:41 ` Oskar Schirmer
2010-05-17 8:41 ` Oskar Schirmer
2010-05-17 23:49 ` Mike Frysinger
2010-05-17 23:49 ` Mike Frysinger
2010-05-18 0:18 ` H Hartley Sweeten
2010-05-18 0:18 ` H Hartley Sweeten
2010-05-18 8:32 ` Oskar Schirmer
2010-05-18 8:32 ` Oskar Schirmer
2010-05-18 9:37 ` Daniel Glöckner
2010-05-18 9:37 ` Daniel Glöckner
2010-05-18 8:34 ` [PATCH v2] " Oskar Schirmer
2010-05-18 8:34 ` Oskar Schirmer
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