linux-kernel - Re: [2.6.35-rc5] select useful number of entries for DMA debugging v3...

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Message-ID: <19516.31370.717799.659547@stoffel.org>
Date:	Tue, 13 Jul 2010 10:39:06 -0400
From:	"John Stoffel" <john@...ffel.org>
To:	Daniel J Blueman <daniel.blueman@...il.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Joerg Roedel <joro@...tes.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	John Stoffel <john@...ffel.org>
Subject: Re: [2.6.35-rc5] select useful number of entries for DMA debugging 
	v3...

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

Signed-off-by: John Stoffel <john@...ffel.org>

>> 
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?

Daniel> Good comment. Fixed checkpatch compliance and rediffed against
Daniel> 2.6.35-rc5. Linus/Ingo - is this more acceptable?

Daniel> ---

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 ~38000
Daniel> entries on a 1GB system), to prevent excessive use.

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

Daniel> diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
Daniel> index 4b7e3d8..5ff7f12 100644
Daniel> --- a/arch/x86/kernel/pci-dma.c
Daniel> +++ b/arch/x86/kernel/pci-dma.c
Daniel> @@ -53,7 +53,7 @@ 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 01e6427..b689ac7 100644
Daniel> --- a/lib/dma-debug.c
Daniel> +++ b/lib/dma-debug.c
Daniel> @@ -487,7 +487,8 @@ static int prealloc_memory(u32 num_entries)
Daniel>  	num_free_entries = num_entries;
Daniel>  	min_free_entries = num_entries;

Daniel> -	pr_info("DMA-API: preallocated %d debug entries\n", num_entries);
Daniel> +	pr_info("DMA-API: preallocated %d debug entries; boot with "
Daniel> +		"dma_debug_entries=N to change\n", num_entries);

Daniel>  	return 0;

Daniel> @@ -736,6 +737,13 @@ void dma_debug_init(u32 num_entries)

Daniel>  	if (req_entries)
Daniel>  		num_entries = req_entries;
Daniel> +	else
Daniel> +		/*
Daniel> +		 * For systems with less memory, limit to a proportional
Daniel> +		 * amount of memory, eg 1GB memory, 4KB pages ~ 38000 entries
Daniel> +		 */
Daniel> +		num_entries = min(num_entries,
Daniel> +			(unsigned int)(totalram_pages >> (PAGE_SHIFT - 10)));

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