linux-kernel - Re: [RFC PATCH 1/7] swiotlb: Instead of tracking the end of the swiotlb region just calculate it

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Date:	Thu, 4 Oct 2012 09:01:08 -0400
From:	Konrad Rzeszutek Wilk <konrad@...nel.org>
To:	Alexander Duyck <alexander.h.duyck@...el.com>
Cc:	konrad.wilk@...cle.com, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, rob@...dley.net, akpm@...ux-foundation.org,
	joerg.roedel@....com, bhelgaas@...gle.com, shuahkhan@...il.com,
	linux-kernel@...r.kernel.org, devel@...uxdriverproject.org,
	x86@...nel.org
Subject: Re: [RFC PATCH 1/7] swiotlb: Instead of tracking the end of the
 swiotlb region just calculate it

On Wed, Oct 03, 2012 at 05:38:47PM -0700, Alexander Duyck wrote:
> In the case of swiotlb we already have the start of the region and the number
> of slabs that give us the region size.  Instead of having to call
> virt_to_phys on two pointers we can just take advantage of the fact that the
> region is linear and just compute the end based on the start plus the size.

Why not take advantage of 'the fact that the region is linear' and just
pre-compute the end in swiotlb_init_with_tbl?

That way the logic in is_swiotlb_buffer is even simpler?

> 
> Signed-off-by: Alexander Duyck <alexander.h.duyck@...el.com>
> ---
> 
>  lib/swiotlb.c |   25 ++++++++++++-------------
>  1 files changed, 12 insertions(+), 13 deletions(-)
> 
> diff --git a/lib/swiotlb.c b/lib/swiotlb.c
> index f114bf6..5cc4d4e 100644
> --- a/lib/swiotlb.c
> +++ b/lib/swiotlb.c
> @@ -57,11 +57,11 @@ int swiotlb_force;
>   * swiotlb_tbl_sync_single_*, to see if the memory was in fact allocated by this
>   * API.
>   */
> -static char *io_tlb_start, *io_tlb_end;
> +static char *io_tlb_start;
>  
>  /*
> - * The number of IO TLB blocks (in groups of 64) between io_tlb_start and
> - * io_tlb_end.  This is command line adjustable via setup_io_tlb_npages.
> + * The number of IO TLB blocks (in groups of 64).
> + * This is command line adjustable via setup_io_tlb_npages.
>   */
>  static unsigned long io_tlb_nslabs;
>  
> @@ -128,11 +128,11 @@ void swiotlb_print_info(void)
>  	phys_addr_t pstart, pend;
>  
>  	pstart = virt_to_phys(io_tlb_start);
> -	pend = virt_to_phys(io_tlb_end);
> +	pend = pstart + bytes;
>  
>  	printk(KERN_INFO "software IO TLB [mem %#010llx-%#010llx] (%luMB) mapped at [%p-%p]\n",
>  	       (unsigned long long)pstart, (unsigned long long)pend - 1,
> -	       bytes >> 20, io_tlb_start, io_tlb_end - 1);
> +	       bytes >> 20, io_tlb_start, io_tlb_start + bytes - 1);
>  }
>  
>  void __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
> @@ -143,12 +143,10 @@ void __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
>  
>  	io_tlb_nslabs = nslabs;
>  	io_tlb_start = tlb;
> -	io_tlb_end = io_tlb_start + bytes;
>  
>  	/*
>  	 * Allocate and initialize the free list array.  This array is used
>  	 * to find contiguous free memory regions of size up to IO_TLB_SEGSIZE
> -	 * between io_tlb_start and io_tlb_end.
>  	 */
>  	io_tlb_list = alloc_bootmem_pages(PAGE_ALIGN(io_tlb_nslabs * sizeof(int)));
>  	for (i = 0; i < io_tlb_nslabs; i++)
> @@ -254,14 +252,12 @@ swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs)
>  
>  	io_tlb_nslabs = nslabs;
>  	io_tlb_start = tlb;
> -	io_tlb_end = io_tlb_start + bytes;
>  
>  	memset(io_tlb_start, 0, bytes);
>  
>  	/*
>  	 * Allocate and initialize the free list array.  This array is used
>  	 * to find contiguous free memory regions of size up to IO_TLB_SEGSIZE
> -	 * between io_tlb_start and io_tlb_end.
>  	 */
>  	io_tlb_list = (unsigned int *)__get_free_pages(GFP_KERNEL,
>  	                              get_order(io_tlb_nslabs * sizeof(int)));
> @@ -304,7 +300,6 @@ cleanup3:
>  	                                                 sizeof(int)));
>  	io_tlb_list = NULL;
>  cleanup2:
> -	io_tlb_end = NULL;
>  	io_tlb_start = NULL;
>  	io_tlb_nslabs = 0;
>  	return -ENOMEM;
> @@ -339,8 +334,10 @@ void __init swiotlb_free(void)
>  
>  static int is_swiotlb_buffer(phys_addr_t paddr)
>  {
> -	return paddr >= virt_to_phys(io_tlb_start) &&
> -		paddr < virt_to_phys(io_tlb_end);
> +	phys_addr_t swiotlb_start = virt_to_phys(io_tlb_start);
> +
> +	return paddr >= swiotlb_start &&
> +		paddr < (swiotlb_start + (io_tlb_nslabs << IO_TLB_SHIFT));
>  }
>  
>  /*
> @@ -938,6 +935,8 @@ EXPORT_SYMBOL(swiotlb_dma_mapping_error);
>  int
>  swiotlb_dma_supported(struct device *hwdev, u64 mask)
>  {
> -	return swiotlb_virt_to_bus(hwdev, io_tlb_end - 1) <= mask;
> +	unsigned long bytes = io_tlb_nslabs << IO_TLB_SHIFT;
> +
> +	return swiotlb_virt_to_bus(hwdev, io_tlb_start + bytes - 1) <= mask;
>  }
>  EXPORT_SYMBOL(swiotlb_dma_supported);
> 
> --
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