Messages in this thread Patch in this message | | | Date | Sun, 11 Jul 2010 14:00:03 +0100 | Subject | Re: [2.6.35-rc3] select useful number of entries for DMA debugging... | From | Daniel J Blueman <> |
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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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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