Message-ID: <5094159C.6020801@intel.com>
Date:	Fri, 02 Nov 2012 11:49:00 -0700
From:	Alexander Duyck <alexander.h.duyck@...el.com>
To:	Konrad Rzeszutek Wilk <konrad@...nel.org>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Alexander Duyck <alexander.duyck@...il.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 v3 0/7] Improve swiotlb performance by using physical
 addresses

On 11/02/2012 09:21 AM, Konrad Rzeszutek Wilk wrote:
> On Mon, Oct 29, 2012 at 03:05:56PM -0400, Konrad Rzeszutek Wilk wrote:
>> On Mon, Oct 29, 2012 at 11:18:09AM -0700, Alexander Duyck wrote:
>>> On Mon, Oct 15, 2012 at 10:19 AM, Alexander Duyck
>>> <alexander.h.duyck@...el.com> wrote:
>>>> While working on 10Gb/s routing performance I found a significant amount of
>>>> time was being spent in the swiotlb DMA handler. Further digging found that a
>>>> significant amount of this was due to virtual to physical address translation
>>>> and calling the function that did it. It accounted for nearly 60% of the
>>>> total swiotlb overhead.
>>>>
>>>> This patch set works to resolve that by replacing the io_tlb_start and
>>>> io_tlb_end virtual addresses with a physical addresses. In addition it changes
>>>> the io_tlb_overflow_buffer from a virtual to a physical address. I followed
>>>> through with the cleanup to the point that the only functions that really
>>>> require the virtual address for the DMA buffer are the init, free, and
>>>> bounce functions.
>>>>
>>>> In the case of devices that are using the bounce buffers these patches should
>>>> result in only a slight performance gain if any. This is due to the locking
>>>> overhead required to map and unmap the buffers.
>>>>
>>>> In the case of devices that are not making use of bounce buffers these patches
>>>> can significantly reduce their overhead. In the case of an ixgbe routing test
>>>> for example, these changes result in 7 fewer calls to __phys_addr and
>>>> allow is_swiotlb_buffer to become inlined due to a reduction in the number of
>>>> instructions. When running a routing throughput test using small packets I
>>>> saw roughly a 6% increase in packets rates after applying these patches. This
>>>> appears to match up with the CPU overhead reduction I was tracking via perf.
>>>>
>>>> Before:
>>>> Results 10.0Mpps
>>>>
>>>> After:
>>>> Results 10.6Mpps
>>>>
>>>> Finally, I updated the parameter names for several of the core function calls
>>>> as there was some ambiguity in naming. Specifically virtual address pointers
>>>> were named dma_addr. When I changed these pointers to physical I instead used
>>>> the name tlb_addr as this value represented a physical address in the
>>>> io_tlb_start region and is less likely to be confused with a bus address.
>>>>
>>>> v2:
>>>> I reviewed the changes and realized that the first patch that was dropping
>>>> io_tlb_end and calculating the value didn't actually gain me much once I had
>>>> gone through and translated the rest of the addresses to physical addresses.
>>>> As such I have updated the patch so that it instead is converting io_tlb_end
>>>> from a virtual address to a physical address.  This actually helps to reduce
>>>> the overhead for is_swiotlb_buffer and swiotlb_dma_supported by several
>>>> instructions.
>>>>
>>>> v3:
>>>> After reviewing the patches I realized I was causing some namespace pollution
>>>> since a "static char *" was being replaced with "phys_addr_t" when it should
>>>> have been "static phys_addr_t".  As such I have updated the first 3 patches to
>>>> correctly replace static pointers with static physical addresses.
>>>>
>>>> ---
>>>>
>>>> Alexander Duyck (7):
>>>>       swiotlb:  Do not export swiotlb_bounce since there are no external consumers
>>>>       swiotlb: Use physical addresses instead of virtual in swiotlb_tbl_sync_single
>>>>       swiotlb: Use physical addresses for swiotlb_tbl_unmap_single
>>>>       swiotlb: Return physical addresses when calling swiotlb_tbl_map_single
>>>>       swiotlb: Make io_tlb_overflow_buffer a physical address
>>>>       swiotlb: Make io_tlb_start a physical address instead of a virtual one
>>>>       swiotlb: Make io_tlb_end a physical address instead of a virtual one
>>>>
>>>>
>>>>  drivers/xen/swiotlb-xen.c |   25 ++--
>>>>  include/linux/swiotlb.h   |   20 ++-
>>>>  lib/swiotlb.c             |  269 +++++++++++++++++++++++----------------------
>>>>  3 files changed, 163 insertions(+), 151 deletions(-)
>>>>
>>> Is there any ETA on when this patch series might be pulled into a
>>> tree?  I'm just wondering if I need to rebase this patch series and
>>> resubmit it, and if so what tree I need to rebase it off of?
>> No need to rebase it. I did a test on V2 version with Xen, but I still
>> need to do a IA64/Calgary/AMD Vi/Intel VT-d/GART test before
>> pushing it out.
> So you should your patches in linux-next.

I see they are in there.  Thanks.
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