Messages in this thread Patch in this message | | | Date | Mon, 12 Jul 2010 10:39:04 -0400 | From | "John Stoffel" <> | Subject | Re: [2.6.35-rc3] select useful number of entries for DMA debugging... |
| |
>>>>> "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
-- 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/
| |