[2.6.35-rc3] select useful number of entries for DMA debugging...

[2.6.35-rc3] select useful number of entries for DMA debugging...

[Daniel J Blueman]

When booting 2.6.35-rc3 on some different x86 boxes with DMA debugging
enabled, I've consistently seen it exhaust the allocated entries during
boot, giving 'DMA-API: debugging out of memory - disabling'.

Increase number of entries to allow DMA debugging again.

Signed-off-by: Daniel J Blueman <daniel.blueman@gmail.com>

diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
index 4b7e3d8..5ff7f12 100644
--- a/arch/x86/kernel/pci-dma.c
+++ b/arch/x86/kernel/pci-dma.c
@@ -53,7 +53,7 @@ struct device x86_dma_fallback_dev = {
 EXPORT_SYMBOL(x86_dma_fallback_dev);

 /* Number of entries preallocated for DMA-API debugging */
-#define PREALLOC_DMA_DEBUG_ENTRIES       32768
+#define PREALLOC_DMA_DEBUG_ENTRIES       65536

 int dma_set_mask(struct device *dev, u64 mask)
 {
-- 
Daniel J Blueman

Re: [2.6.35-rc3] select useful number of entries for DMA debugging...

[Linus Torvalds]

On Mon, Jul 5, 2010 at 1:35 AM, Daniel J Blueman
<daniel.blueman@gmail.com> wrote:
> When booting 2.6.35-rc3 on some different x86 boxes with DMA debugging
> enabled, I've consistently seen it exhaust the allocated entries during
> boot, giving 'DMA-API: debugging out of memory - disabling'.
>
> Increase number of entries to allow DMA debugging again.

Rather than increase the default that gets allocated whenever anybody
enables the DMA debugging, I'd really prefer to see people use the
kernel command line option if they run out. After all, it's a (pretty
esoteric) debug option, and the number of required entries depends on
machine configuration. I'd rather not make the default cover a huge
number, when you could just add

   dma_debug_entries=65536

on the kernel boot command line instead for machines that want/need it..

                  Linus

Re: [2.6.35-rc3] select useful number of entries for DMA debugging...

[Daniel J Blueman]

On 9 July 2010 22:33, Linus Torvalds <torvalds@linux-foundation.org> wrote:
> On Mon, Jul 5, 2010 at 1:35 AM, Daniel J Blueman
> <daniel.blueman@gmail.com> wrote:
>> When booting 2.6.35-rc3 on some different x86 boxes with DMA debugging
>> enabled, I've consistently seen it exhaust the allocated entries during
>> boot, giving 'DMA-API: debugging out of memory - disabling'.
>>
>> Increase number of entries to allow DMA debugging again.
>
> Rather than increase the default that gets allocated whenever anybody
> enables the DMA debugging, I'd really prefer to see people use the
> kernel command line option if they run out. After all, it's a (pretty
> esoteric) debug option, and the number of required entries depends on
> machine configuration. I'd rather not make the default cover a huge
> number, when you could just add
>
>   dma_debug_entries=65536
>
> on the kernel boot command line instead for machines that want/need it..

That said, I am seeing the DMA pool exhaust on a single socket Core i5
system with Intel graphics and no other adapters - seems like a fairly
common case. If eg 25% of developers will be using similar to this,
maybe it's good to make DMA debugging less immediately esoteric?

On the other hand, I would immediately agree if the exhaustion
occurred on an atypical setup.
-- 
Daniel J Blueman

Re: [2.6.35-rc3] select useful number of entries for DMA debugging...

[Joerg Roedel]

On Sat, Jul 10, 2010 at 03:52:04PM +0100, Daniel J Blueman wrote:
> On 9 July 2010 22:33, Linus Torvalds <torvalds@linux-foundation.org> wrote:
> > On Mon, Jul 5, 2010 at 1:35 AM, Daniel J Blueman
> > <daniel.blueman@gmail.com> wrote:
> >> When booting 2.6.35-rc3 on some different x86 boxes with DMA debugging
> >> enabled, I've consistently seen it exhaust the allocated entries during
> >> boot, giving 'DMA-API: debugging out of memory - disabling'.
> >>
> >> Increase number of entries to allow DMA debugging again.
> >
> > Rather than increase the default that gets allocated whenever anybody
> > enables the DMA debugging, I'd really prefer to see people use the
> > kernel command line option if they run out. After all, it's a (pretty
> > esoteric) debug option, and the number of required entries depends on
> > machine configuration. I'd rather not make the default cover a huge
> > number, when you could just add
> >
> >   dma_debug_entries=65536
> >
> > on the kernel boot command line instead for machines that want/need it..
> 
> That said, I am seeing the DMA pool exhaust on a single socket Core i5
> system with Intel graphics and no other adapters - seems like a fairly
> common case. If eg 25% of developers will be using similar to this,
> maybe it's good to make DMA debugging less immediately esoteric?
> 
> On the other hand, I would immediately agree if the exhaustion
> occurred on an atypical setup.

How much memory do you have in this machine? We could probably make the
number of pre-allocated entries dependent on the memory available in the
machine like Ingo suggested some time ago to avoid such problems.

	Joerg

Re: [2.6.35-rc3] select useful number of entries for DMA debugging...

[Daniel J Blueman]

On 10 July 2010 16:43, Joerg Roedel <joro@8bytes.org> wrote:
> On Sat, Jul 10, 2010 at 03:52:04PM +0100, Daniel J Blueman wrote:
>> On 9 July 2010 22:33, Linus Torvalds <torvalds@linux-foundation.org> wrote:
>> > On Mon, Jul 5, 2010 at 1:35 AM, Daniel J Blueman
>> > <daniel.blueman@gmail.com> wrote:
>> >> When booting 2.6.35-rc3 on some different x86 boxes with DMA debugging
>> >> enabled, I've consistently seen it exhaust the allocated entries during
>> >> boot, giving 'DMA-API: debugging out of memory - disabling'.
>> >>
>> >> Increase number of entries to allow DMA debugging again.
>> >
>> > Rather than increase the default that gets allocated whenever anybody
>> > enables the DMA debugging, I'd really prefer to see people use the
>> > kernel command line option if they run out. After all, it's a (pretty
>> > esoteric) debug option, and the number of required entries depends on
>> > machine configuration. I'd rather not make the default cover a huge
>> > number, when you could just add
>> >
>> >   dma_debug_entries=65536
>> >
>> > on the kernel boot command line instead for machines that want/need it..
>>
>> That said, I am seeing the DMA pool exhaust on a single socket Core i5
>> system with Intel graphics and no other adapters - seems like a fairly
>> common case. If eg 25% of developers will be using similar to this,
>> maybe it's good to make DMA debugging less immediately esoteric?
>>
>> On the other hand, I would immediately agree if the exhaustion
>> occurred on an atypical setup.
>
> How much memory do you have in this machine? We could probably make the
> number of pre-allocated entries dependent on the memory available in the
> machine like Ingo suggested some time ago to avoid such problems.

I have 4GB. Since this change is specific to x86, I guess the only
corner case we need to protect from this change is developers on small
x86 embedded systems such as MIDs, so lowering the allocated size on
<1GB systems makes sense.
-- 
Daniel J Blueman

Re: [2.6.35-rc3] select useful number of entries for DMA debugging...

[Daniel J Blueman]

On 11 July 2010 12:54, Daniel J Blueman <daniel.blueman@gmail.com> wrote:
> On 10 July 2010 16:43, Joerg Roedel <joro@8bytes.org> wrote:
>> On Sat, Jul 10, 2010 at 03:52:04PM +0100, Daniel J Blueman wrote:
>>> On 9 July 2010 22:33, Linus Torvalds <torvalds@linux-foundation.org> wrote:
>>> > On Mon, Jul 5, 2010 at 1:35 AM, Daniel J Blueman
>>> > <daniel.blueman@gmail.com> wrote:
>>> >> When booting 2.6.35-rc3 on some different x86 boxes with DMA debugging
>>> >> enabled, I've consistently seen it exhaust the allocated entries during
>>> >> boot, giving 'DMA-API: debugging out of memory - disabling'.
>>> >>
>>> >> Increase number of entries to allow DMA debugging again.
>>> >
>>> > Rather than increase the default that gets allocated whenever anybody
>>> > enables the DMA debugging, I'd really prefer to see people use the
>>> > kernel command line option if they run out. After all, it's a (pretty
>>> > esoteric) debug option, and the number of required entries depends on
>>> > machine configuration. I'd rather not make the default cover a huge
>>> > number, when you could just add
>>> >
>>> >   dma_debug_entries=65536
>>> >
>>> > on the kernel boot command line instead for machines that want/need it..
>>>
>>> That said, I am seeing the DMA pool exhaust on a single socket Core i5
>>> system with Intel graphics and no other adapters - seems like a fairly
>>> common case. If eg 25% of developers will be using similar to this,
>>> maybe it's good to make DMA debugging less immediately esoteric?
>>>
>>> On the other hand, I would immediately agree if the exhaustion
>>> occurred on an atypical setup.
>>
>> How much memory do you have in this machine? We could probably make the
>> number of pre-allocated entries dependent on the memory available in the
>> machine like Ingo suggested some time ago to avoid such problems.
>
> I have 4GB. Since this change is specific to x86, I guess the only
> corner case we need to protect from this change is developers on small
> x86 embedded systems such as MIDs, so lowering the allocated size on
> <1GB systems makes sense.

How about something like this? If you think ~18800 entries on a 1GB
system is better, let me know and I'll quickly respin. The calculation
seems reasonable for other arches.

When booting 2.6.35-rc3 on some different x86 boxes with DMA debugging
enabled, I've seen consistent exhaustion of the allocated entries during
boot, giving 'DMA-API: debugging out of memory - disabling'.

Increase the default number of entries to allow DMA debugging again, but
assign a reasonable lower limit for systems with less memory (eg ~37600
entries on a 1GB system), to prevent excessive use.

Signed-off-by: Daniel J Blueman <daniel.blueman@gmail.com>

diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
index a4ac764..0766fcf 100644
--- a/arch/x86/kernel/pci-dma.c
+++ b/arch/x86/kernel/pci-dma.c
@@ -52,7 +52,7 @@ struct device x86_dma_fallback_dev = {
 EXPORT_SYMBOL(x86_dma_fallback_dev);

 /* Number of entries preallocated for DMA-API debugging */
-#define PREALLOC_DMA_DEBUG_ENTRIES       32768
+#define PREALLOC_DMA_DEBUG_ENTRIES       65536

 int dma_set_mask(struct device *dev, u64 mask)
 {
diff --git a/lib/dma-debug.c b/lib/dma-debug.c
index ba8b670..2d1f965 100644
--- a/lib/dma-debug.c
+++ b/lib/dma-debug.c
@@ -736,6 +736,10 @@ void dma_debug_init(u32 num_entries)

 	if (req_entries)
 		num_entries = req_entries;
+	else
+		/* for systems with less memory, limit to a proportional amount of memory */
+		/* eg 1GB memory, 4KB pages ~ 37600 entries */
+		num_entries = min(num_entries, (unsigned int)(totalram_pages >>
(PAGE_SHIFT - 10)));

 	if (prealloc_memory(num_entries) != 0) {
 		pr_err("DMA-API: debugging out of memory error - disabled\n");
-- 
Daniel J Blueman

Re: [2.6.35-rc3] select useful number of entries for DMA debugging...

[John Stoffel]

>>>>> "Daniel" == Daniel J Blueman <daniel.blueman@gmail.com> writes:

Daniel> On 11 July 2010 12:54, Daniel J Blueman <daniel.blueman@gmail.com> wrote:
>> On 10 July 2010 16:43, Joerg Roedel <joro@8bytes.org> wrote:
>>> On Sat, Jul 10, 2010 at 03:52:04PM +0100, Daniel J Blueman wrote:
>>>> On 9 July 2010 22:33, Linus Torvalds <torvalds@linux-foundation.org> wrote:
>>>> > On Mon, Jul 5, 2010 at 1:35 AM, Daniel J Blueman
>>>> > <daniel.blueman@gmail.com> wrote:
>>>> >> When booting 2.6.35-rc3 on some different x86 boxes with DMA debugging
>>>> >> enabled, I've consistently seen it exhaust the allocated entries during
>>>> >> boot, giving 'DMA-API: debugging out of memory - disabling'.
>>>> >>
>>>> >> Increase number of entries to allow DMA debugging again.
>>>> >
>>>> > Rather than increase the default that gets allocated whenever anybody
>>>> > enables the DMA debugging, I'd really prefer to see people use the
>>>> > kernel command line option if they run out. After all, it's a (pretty
>>>> > esoteric) debug option, and the number of required entries depends on
>>>> > machine configuration. I'd rather not make the default cover a huge
>>>> > number, when you could just add
>>>> >
>>>> >   dma_debug_entries=65536
>>>> >
>>>> > on the kernel boot command line instead for machines that want/need it..
>>>> 
>>>> That said, I am seeing the DMA pool exhaust on a single socket Core i5
>>>> system with Intel graphics and no other adapters - seems like a fairly
>>>> common case. If eg 25% of developers will be using similar to this,
>>>> maybe it's good to make DMA debugging less immediately esoteric?
>>>> 
>>>> On the other hand, I would immediately agree if the exhaustion
>>>> occurred on an atypical setup.
>>> 
>>> How much memory do you have in this machine? We could probably make the
>>> number of pre-allocated entries dependent on the memory available in the
>>> machine like Ingo suggested some time ago to avoid such problems.
>> 
>> I have 4GB. Since this change is specific to x86, I guess the only
>> corner case we need to protect from this change is developers on small
>> x86 embedded systems such as MIDs, so lowering the allocated size on
>> <1GB systems makes sense.

Daniel> How about something like this? If you think ~18800 entries on a 1GB
Daniel> system is better, let me know and I'll quickly respin. The calculation
Daniel> seems reasonable for other arches.

Daniel> When booting 2.6.35-rc3 on some different x86 boxes with DMA debugging
Daniel> enabled, I've seen consistent exhaustion of the allocated entries during
Daniel> boot, giving 'DMA-API: debugging out of memory - disabling'.

Daniel> Increase the default number of entries to allow DMA debugging again, but
Daniel> assign a reasonable lower limit for systems with less memory (eg ~37600
Daniel> entries on a 1GB system), to prevent excessive use.

Daniel> Signed-off-by: Daniel J Blueman <daniel.blueman@gmail.com>

Daniel> diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
Daniel> index a4ac764..0766fcf 100644
Daniel> --- a/arch/x86/kernel/pci-dma.c
Daniel> +++ b/arch/x86/kernel/pci-dma.c
Daniel> @@ -52,7 +52,7 @@ struct device x86_dma_fallback_dev = {
Daniel>  EXPORT_SYMBOL(x86_dma_fallback_dev);

Daniel>  /* Number of entries preallocated for DMA-API debugging */
Daniel> -#define PREALLOC_DMA_DEBUG_ENTRIES       32768
Daniel> +#define PREALLOC_DMA_DEBUG_ENTRIES       65536

Daniel>  int dma_set_mask(struct device *dev, u64 mask)
Daniel>  {
Daniel> diff --git a/lib/dma-debug.c b/lib/dma-debug.c
Daniel> index ba8b670..2d1f965 100644
Daniel> --- a/lib/dma-debug.c
Daniel> +++ b/lib/dma-debug.c
Daniel> @@ -736,6 +736,10 @@ void dma_debug_init(u32 num_entries)

Daniel>  	if (req_entries)
Daniel>  		num_entries = req_entries;
Daniel> +	else
Daniel> +		/* for systems with less memory, limit to a proportional amount of memory */
Daniel> +		/* eg 1GB memory, 4KB pages ~ 37600 entries */
Daniel> +		num_entries = min(num_entries, (unsigned int)(totalram_pages >>
Daniel> (PAGE_SHIFT - 10)));

Daniel>  	if (prealloc_memory(num_entries) != 0) {
Daniel>  		pr_err("DMA-API: debugging out of memory error - disabled\n");

Maybe you could update this to mention the kernel parameter
"dma_debug_entries=xxxxx" so that people could use to increase this
value?  It would make it simpler and easier to find it it's logged
nicely?

Thanks,
John