| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Date: Wed, 15 Apr 2020 09:57:16 +0200
From: Christian König <christian.koenig@....com>
To: Jani Nikula <jani.nikula@...ux.intel.com>,
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>,
Xiaojie Yuan <xiaojie.yuan@....com>
Subject: Re: [PATCH] Optimized division operation to shift operation
Am 15.04.20 um 09:41 schrieb Jani Nikula:
> 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.
I have similar worries, especially since we replace the "/ (4 * 2)" with
">> 3" it's making the code just a bit less readable.
And that the code runs exactly once while loading the driver and pushing
the firmware into the hardware. So performance is completely irrelevant
here.
Regards,
Christian.
>
> 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://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flists.freedesktop.org%2Fmailman%2Flistinfo%2Famd-gfx&data=02%7C01%7Cchristian.koenig%40amd.com%7C1e91f7edcfe0473b0d7008d7e11074a8%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637225333103893889&sdata=VDJlEY2%2Bl1SSO8Fw1dYqqPFqQtyHpsxQ0Tm7iVOgJQY%3D&reserved=0
>> _______________________________________________
>> dri-devel mailing list
>> dri-devel@...ts.freedesktop.org
>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flists.freedesktop.org%2Fmailman%2Flistinfo%2Fdri-devel&data=02%7C01%7Cchristian.koenig%40amd.com%7C1e91f7edcfe0473b0d7008d7e11074a8%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637225333103893889&sdata=EpqRRbCiksur%2BjMlVQplExuJsmw6UPODhyBOutOVukw%3D&reserved=0
Powered by blists - more mailing lists