Re: [PATCH v2 1/2] swiotlb: add debugfs to track swiotlb buffer usage

Tim Chen
2018-12-10T20:00:23Z

On 12/9/18 4:37 PM, Dongli Zhang wrote:

>
> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index 045930e..3979c2c 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -35,6 +35,9 @@
> #include <linux/scatterlist.h>
> #include <linux/mem_encrypt.h>
> #include <linux/set_memory.h>
> +#ifdef CONFIG_DEBUG_FS
> +#include <linux/debugfs.h>
> +#endif

Seems like #ifdef CONFIG_DEBUG_FS is better located inside debugfs.h,
instead of requiring every file that includes it
to have a #ifdef CONFIG_DEBUG_FS.

>
> #include <asm/io.h>
> #include <asm/dma.h>
> @@ -73,6 +76,13 @@ static phys_addr_t io_tlb_start, io_tlb_end;
> */
> static unsigned long io_tlb_nslabs;
>
> +#ifdef CONFIG_DEBUG_FS
> +/*
> + * The number of used IO TLB block
> + */
> +static unsigned long io_tlb_used;
> +#endif
> +
> /*
> * This is a free list describing the number of free entries available from
> * each index
> @@ -528,6 +538,9 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
> dev_warn(hwdev, "swiotlb buffer is full (sz: %zd bytes)\n", size);
> return SWIOTLB_MAP_ERROR;
> found:
> +#ifdef CONFIG_DEBUG_FS
> + io_tlb_used += nslots;
> +#endif

One nit I have about this patch is there are too many CONFIG_DEBUG_FS.

For example here, instead of io_tlb_used, we can have a macro defined,
perhaps something like inc_iotlb_used(nslots). It can be placed in the
same section that swiotlb_create_debugfs is defined so there's a single
place where all the CONFIG_DEBUG_FS stuff is located.

Then define inc_iotlb_used to be null when we don't have
CONFIG_DEBUG_FS.

> spin_unlock_irqrestore(&io_tlb_lock, flags);
>
> /*
> @@ -588,6 +601,10 @@ void swiotlb_tbl_unmap_single(struct device *hwdev, phys_addr_t tlb_addr,
> */
> for (i = index - 1; (OFFSET(i, IO_TLB_SEGSIZE) != IO_TLB_SEGSIZE -1) && io_tlb_list[i]; i--)
> io_tlb_list[i] = ++count;
> +
> +#ifdef CONFIG_DEBUG_FS
> + io_tlb_used -= nslots;
> +#endif
> }
> spin_unlock_irqrestore(&io_tlb_lock, flags);
> }
> @@ -883,3 +900,36 @@ const struct dma_map_ops swiotlb_dma_ops = {
> .dma_supported = dma_direct_supported,
> };
> EXPORT_SYMBOL(swiotlb_dma_ops);
> +
> +#ifdef CONFIG_DEBUG_FS
> +

Maybe move io_tlb_used definition here and define
inc_iotlb_used here.

> +static int __init swiotlb_create_debugfs(void)
> +{
> + static struct dentry *d_swiotlb_usage;
> + struct dentry *ent;
> +
> + d_swiotlb_usage = debugfs_create_dir("swiotlb", NULL);
> +
> + if (!d_swiotlb_usage)
> + return -ENOMEM;
> +
> + ent = debugfs_create_ulong("io_tlb_nslabs", 0400,
> + d_swiotlb_usage, &io_tlb_nslabs);
> + if (!ent)
> + goto fail;
> +
> + ent = debugfs_create_ulong("io_tlb_used", 0400,
> + d_swiotlb_usage, &io_tlb_used);
> + if (!ent)
> + goto fail;
> +
> + return 0;
> +
> +fail:
> + debugfs_remove_recursive(d_swiotlb_usage);
> + return -ENOMEM;
> +}
> +
> +late_initcall(swiotlb_create_debugfs);
> +
> +#endif
>

Thanks.

Tim