Re: [PATCH] Optimized division operation to shift operation

From: Jani Nikula <jani.nikula@linux.intel.com>
To: Alex Deucher <alexdeucher@gmail.com>, Bernard Zhao <bernard@vivo.com>
Cc: "Alex Sierra" <alex.sierra@amd.com>,
	"David Airlie" <airlied@linux.ie>, "Oak Zeng" <Oak.Zeng@amd.com>,
	LKML <linux-kernel@vger.kernel.org>,
	"Maling list - DRI developers" <dri-devel@lists.freedesktop.org>,
	"Christian König" <christian.koenig@amd.com>,
	kernel@vivo.com, "Huang Rui" <ray.huang@amd.com>,
	"amd-gfx list" <amd-gfx@lists.freedesktop.org>,
	"Alex Deucher" <alexander.deucher@amd.com>,
	"Xiaojie Yuan" <xiaojie.yuan@amd.com>,
	"Sam Ravnborg" <sam@ravnborg.org>,
	"Felix Kuehling" <Felix.Kuehling@amd.com>,
	"Kent Russell" <kent.russell@amd.com>
Subject: Re: [PATCH] Optimized division operation to shift operation
Date: Wed, 15 Apr 2020 10:41:37 +0300	[thread overview]
Message-ID: <87lfmx5h72.fsf@intel.com> (raw)
In-Reply-To: <CADnq5_Phca3L-HGOQz0DPBoARHgwcJRK_a7-WmeFMPkrPWeOeg@mail.gmail.com>

On Tue, 14 Apr 2020, Alex Deucher <alexdeucher@gmail.com> wrote:
> On Tue, Apr 14, 2020 at 9:05 AM Bernard Zhao <bernard@vivo.com> wrote:
>>
>> On some processors, the / operate will call the compiler`s div lib,
>> which is low efficient, We can replace the / operation with shift,
>> so that we can replace the call of the division library with one
>> shift assembly instruction.

This was applied already, and it's not in a driver I look after... but
to me this feels like something that really should be
justified. Using >> instead of / for multiples of 2 division mattered 20
years ago, I'd be surprised if it still did on modern compilers.

BR,
Jani.

>>
>> Signed-off-by: Bernard Zhao <bernard@vivo.com>
>
> Applied.  thanks.
>
> Alex
>
>> ---
>>  drivers/gpu/drm/amd/amdgpu/gmc_v6_0.c | 4 ++--
>>  drivers/gpu/drm/amd/amdgpu/gmc_v7_0.c | 4 ++--
>>  drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c | 4 ++--
>>  3 files changed, 6 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/gmc_v6_0.c b/drivers/gpu/drm/amd/amdgpu/gmc_v6_0.c
>> index b205039..66cd078 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/gmc_v6_0.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/gmc_v6_0.c
>> @@ -175,10 +175,10 @@ static int gmc_v6_0_mc_load_microcode(struct amdgpu_device *adev)
>>         amdgpu_ucode_print_mc_hdr(&hdr->header);
>>
>>         adev->gmc.fw_version = le32_to_cpu(hdr->header.ucode_version);
>> -       regs_size = le32_to_cpu(hdr->io_debug_size_bytes) / (4 * 2);
>> +       regs_size = le32_to_cpu(hdr->io_debug_size_bytes) >> 3;
>>         new_io_mc_regs = (const __le32 *)
>>                 (adev->gmc.fw->data + le32_to_cpu(hdr->io_debug_array_offset_bytes));
>> -       ucode_size = le32_to_cpu(hdr->header.ucode_size_bytes) / 4;
>> +       ucode_size = le32_to_cpu(hdr->header.ucode_size_bytes) >> 2;
>>         new_fw_data = (const __le32 *)
>>                 (adev->gmc.fw->data + le32_to_cpu(hdr->header.ucode_array_offset_bytes));
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/gmc_v7_0.c b/drivers/gpu/drm/amd/amdgpu/gmc_v7_0.c
>> index 9da9596..ca26d63 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/gmc_v7_0.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/gmc_v7_0.c
>> @@ -193,10 +193,10 @@ static int gmc_v7_0_mc_load_microcode(struct amdgpu_device *adev)
>>         amdgpu_ucode_print_mc_hdr(&hdr->header);
>>
>>         adev->gmc.fw_version = le32_to_cpu(hdr->header.ucode_version);
>> -       regs_size = le32_to_cpu(hdr->io_debug_size_bytes) / (4 * 2);
>> +       regs_size = le32_to_cpu(hdr->io_debug_size_bytes) >> 3;
>>         io_mc_regs = (const __le32 *)
>>                 (adev->gmc.fw->data + le32_to_cpu(hdr->io_debug_array_offset_bytes));
>> -       ucode_size = le32_to_cpu(hdr->header.ucode_size_bytes) / 4;
>> +       ucode_size = le32_to_cpu(hdr->header.ucode_size_bytes) >> 2;
>>         fw_data = (const __le32 *)
>>                 (adev->gmc.fw->data + le32_to_cpu(hdr->header.ucode_array_offset_bytes));
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c b/drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c
>> index 27d83204..295039c 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c
>> @@ -318,10 +318,10 @@ static int gmc_v8_0_tonga_mc_load_microcode(struct amdgpu_device *adev)
>>         amdgpu_ucode_print_mc_hdr(&hdr->header);
>>
>>         adev->gmc.fw_version = le32_to_cpu(hdr->header.ucode_version);
>> -       regs_size = le32_to_cpu(hdr->io_debug_size_bytes) / (4 * 2);
>> +       regs_size = le32_to_cpu(hdr->io_debug_size_bytes) >> 3;
>>         io_mc_regs = (const __le32 *)
>>                 (adev->gmc.fw->data + le32_to_cpu(hdr->io_debug_array_offset_bytes));
>> -       ucode_size = le32_to_cpu(hdr->header.ucode_size_bytes) / 4;
>> +       ucode_size = le32_to_cpu(hdr->header.ucode_size_bytes) >> 2;
>>         fw_data = (const __le32 *)
>>                 (adev->gmc.fw->data + le32_to_cpu(hdr->header.ucode_array_offset_bytes));
>>
>> --
>> 2.7.4
>>
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>> amd-gfx@lists.freedesktop.org
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-- 
Jani Nikula, Intel Open Source Graphics Center
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