linux-kernel - Re: [PATCH] Optimized division operation to shift operation

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

On Tue, 14 Apr 2020, Alex Deucher <alexdeucher@...il.com> wrote:
> On Tue, Apr 14, 2020 at 9:05 AM Bernard Zhao <bernard@...o.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@...o.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
>>
>> _______________________________________________
>> amd-gfx mailing list
>> amd-gfx@...ts.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/amd-gfx
> _______________________________________________
> dri-devel mailing list
> dri-devel@...ts.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Jani Nikula, Intel Open Source Graphics Center

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