linux-kernel - Re: [PATCH v2 1/7] swiotlb: Make io_tlb_end a physical address instead of a virtual one

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Message-ID: <507C2F20.8000504@intel.com>
Date:	Mon, 15 Oct 2012 08:43:28 -0700
From:	Alexander Duyck <alexander.h.duyck@...el.com>
To:	Hillf Danton <dhillf@...il.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,
	fujita.tomonori@....ntt.co.jp, linux-kernel@...r.kernel.org,
	x86@...nel.org
Subject: Re: [PATCH v2 1/7] swiotlb: Make io_tlb_end a physical address instead
 of a virtual one

On 10/13/2012 05:52 AM, Hillf Danton wrote:
> Hi Alexander,
>
> On Fri, Oct 12, 2012 at 4:34 AM, Alexander Duyck
> <alexander.h.duyck@...el.com> wrote:
>> This change replaces all references to the virtual address for io_tlb_end
>> with references to the physical address io_tlb_end.  The main advantage of
>> replacing the virtual address with a physical address is that we can avoid
>> having to do multiple translations from the virtual address to the physical
>> one needed for testing an existing DMA address.
>>
>> Signed-off-by: Alexander Duyck <alexander.h.duyck@...el.com>
>> ---
>>
>>  lib/swiotlb.c |   24 +++++++++++++-----------
>>  1 files changed, 13 insertions(+), 11 deletions(-)
>>
>> diff --git a/lib/swiotlb.c b/lib/swiotlb.c
>> index f114bf6..19aac9f 100644
>> --- a/lib/swiotlb.c
>> +++ b/lib/swiotlb.c
>> @@ -57,7 +57,8 @@ 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;
>> +phys_addr_t io_tlb_end;
> If add io_tlb_start_phy and io_tlb_end_phy, could we get same results
> with less hunks?
>
> Hillf

What do you mean by less hunks?  Are you referring to the memory space? 
If so, then the patches I am submitting do not impact how much space is
used for the bounce buffer.  The only real result of these patches is
that the total code path is significantly reduced since we don't have to
perform any virtual to physical translations in the hot-path.

Thanks,

Alex
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