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SubjectRe: [PATCH] dma-debug: Kconfig for PREALLOC_DMA_DEBUG_ENTRIES
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On 30/11/2018 17:54, Qian Cai wrote:
> The amount of DMA mappings from Hisilicon HNS ethernet devices is huge,
> so it could trigger "DMA-API: debugging out of memory - disabling".
>
> hnae_get_handle [1]
> hnae_init_queue
> hnae_init_ring
> hnae_alloc_buffers [2]
> debug_dma_map_page
> dma_entry_alloc
>
> [1] for (i = 0; i < handle->q_num; i++)
> [2] for (i = 0; i < ring->desc_num; i++)
>
> On this Huawei TaiShan 2280 aarch64 server, it has reached the limit
> already,
>
> 4 (ports) x 16 (handles) x 1024 (rings) = 65536
>
> Added a Kconfig entry for PREALLOC_DMA_DEBUG_ENTRIES, so make it easier
> for users to deal with special cases like this.
>
> Signed-off-by: Qian Cai <cai@gmx.us>
> ---
> kernel/dma/debug.c | 9 ++-------
> lib/Kconfig.debug | 9 +++++++++
> 2 files changed, 11 insertions(+), 7 deletions(-)

Oh, right, the arch overrides actually got cleaned up already. I'd
forgotten that...

> diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c
> index 231ca4628062..3752fb23f72f 100644
> --- a/kernel/dma/debug.c
> +++ b/kernel/dma/debug.c
> @@ -41,11 +41,6 @@
> #define HASH_FN_SHIFT 13
> #define HASH_FN_MASK (HASH_SIZE - 1)
>
> -/* allow architectures to override this if absolutely required */
> -#ifndef PREALLOC_DMA_DEBUG_ENTRIES
> -#define PREALLOC_DMA_DEBUG_ENTRIES (1 << 16)
> -#endif
> -
> enum {
> dma_debug_single,
> dma_debug_page,
> @@ -132,7 +127,7 @@ static u32 min_free_entries;
> static u32 nr_total_entries;
>
> /* number of preallocated entries requested by kernel cmdline */
> -static u32 nr_prealloc_entries = PREALLOC_DMA_DEBUG_ENTRIES;
> +static u32 nr_prealloc_entries = CONFIG_PREALLOC_DMA_DEBUG_ENTRIES;
>
> /* debugfs dentry's for the stuff above */
> static struct dentry *dma_debug_dent __read_mostly;
> @@ -1063,7 +1058,7 @@ static __init int dma_debug_entries_cmdline(char *str)
> if (!str)
> return -EINVAL;
> if (!get_option(&str, &nr_prealloc_entries))
> - nr_prealloc_entries = PREALLOC_DMA_DEBUG_ENTRIES;
> + nr_prealloc_entries = CONFIG_PREALLOC_DMA_DEBUG_ENTRIES;
> return 0;
> }
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 1af29b8224fd..2c281edcb5ad 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1659,6 +1659,15 @@ config DMA_API_DEBUG
>
> If unsure, say N.
>
> +config PREALLOC_DMA_DEBUG_ENTRIES
> + int "Preallocated DMA-API debugging entries"
> + depends on DMA_API_DEBUG
> + default 65536

I was assuming the point was to also add something like

default 131072 if HNS_ENET

so that DMA debug doesn't require too much thought from the user. If
they still have to notice the overflow message and empirically figure
out a value that does work, rebuilding the kernel each time is far less
convenient than simply adding "dma_debug_entries=..." to their kernel
command line and rebooting, which they can do today. If they do already
know up-front that the default will need overriding and what the
appropriate value is, then the command line still seems seems just as
convenient.

Robin.

> + help
> + The number of preallocated entries for DMA-API debugging code. One
> + entry is required per DMA-API allocation. Increase this if the DMA-API
> + debugging code disables itself because the default is too low.
> +
> config DMA_API_DEBUG_SG
> bool "Debug DMA scatter-gather usage"
> default y
>

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