Re: [PATCH v9 07/15] drm: Add a prefetching memcpy_from_wc

From: "Thomas Hellström" <thomas.hellstrom@linux.intel.com>
To: Jani Nikula <jani.nikula@linux.intel.com>,
	intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org
Subject: Re: [PATCH v9 07/15] drm: Add a prefetching memcpy_from_wc
Date: Wed, 2 Jun 2021 19:26:15 +0200	[thread overview]
Message-ID: <1aa312f7-2c02-c92b-7a71-335a6baea796@linux.intel.com> (raw)
In-Reply-To: <87im2xrcqu.fsf@intel.com>

On 6/1/21 2:27 PM, Jani Nikula wrote:
> On Tue, 01 Jun 2021, Thomas Hellström <thomas.hellstrom@linux.intel.com> wrote:
>> Reading out of write-combining mapped memory is typically very slow
>> since the CPU doesn't prefetch. However some archs have special
>> instructions to do this.
>>
>> So add a best-effort memcpy_from_wc taking dma-buf-map pointer
>> arguments that attempts to use a fast prefetching memcpy and
>> otherwise falls back to ordinary memcopies, taking the iomem tagging
>> into account.
>>
>> The code is largely copied from i915_memcpy_from_wc.
>>
>> Cc: Daniel Vetter <daniel@ffwll.ch>
>> Cc: Christian König <christian.koenig@amd.com>
>> Suggested-by: Daniel Vetter <daniel@ffwll.ch>
>> Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
>> Acked-by: Christian König <christian.koenig@amd.com>
>> Acked-by: Daniel Vetter <daniel@ffwll.ch>
>> ---
>> v7:
>> - Perform a memcpy even if warning with in_interrupt(). Suggested by
>>    Christian König.
>> - Fix compilation failure on !X86 (Reported by kernel test robot
>>    lkp@intel.com)
>> v8:
>> - Skip kerneldoc for drm_memcpy_init_early()
>> - Export drm_memcpy_from_wc() also for non-x86.
>> ---
>>   Documentation/gpu/drm-mm.rst |   2 +-
>>   drivers/gpu/drm/drm_cache.c  | 148 +++++++++++++++++++++++++++++++++++
>>   drivers/gpu/drm/drm_drv.c    |   2 +
>>   include/drm/drm_cache.h      |   7 ++
>>   4 files changed, 158 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/gpu/drm-mm.rst b/Documentation/gpu/drm-mm.rst
>> index 21be6deadc12..c66058c5bce7 100644
>> --- a/Documentation/gpu/drm-mm.rst
>> +++ b/Documentation/gpu/drm-mm.rst
>> @@ -469,7 +469,7 @@ DRM MM Range Allocator Function References
>>   .. kernel-doc:: drivers/gpu/drm/drm_mm.c
>>      :export:
>>   
>> -DRM Cache Handling
>> +DRM Cache Handling and Fast WC memcpy()
>>   ==================
> The title underline needs to be as long as the title.
>
> BR,
> Jani.

Thanks, Jani.

I think Daniel was trying to point this out to me as well with limited 
success. It's fixed now.

/Thomas