[PATCH 2/3] drm/amdgpu: add AMDGPU_VM_NOALLOC
Marek Olšák
maraeo at gmail.com
Mon May 16 11:10:58 UTC 2022
I forgot to say: The NOALLOC flag causes an allocation failure, so there is
a kernel bug somewhere.
Marek
On Mon, May 16, 2022 at 7:06 AM Marek Olšák <maraeo at gmail.com> wrote:
> FYI, I think it's time to merge this because the Mesa commits are going to
> be merged in ~30 minutes if Gitlab CI is green, and that includes updated
> amdgpu_drm.h.
>
> Marek
>
> On Wed, May 11, 2022 at 2:55 PM Marek Olšák <maraeo at gmail.com> wrote:
>
>> Ok sounds good.
>>
>> Marek
>>
>> On Wed., May 11, 2022, 03:43 Christian König, <
>> ckoenig.leichtzumerken at gmail.com> wrote:
>>
>>> It really *is* a NOALLOC feature. In other words there is no latency
>>> improvement on reads because the cache is always checked, even with the
>>> noalloc flag set.
>>>
>>> The only thing it affects is that misses not enter the cache and so
>>> don't cause any additional pressure on evicting cache lines.
>>>
>>> You might want to double check with the hardware guys, but I'm something
>>> like 95% sure that it works this way.
>>>
>>> Christian.
>>>
>>> Am 11.05.22 um 09:22 schrieb Marek Olšák:
>>>
>>> Bypass means that the contents of the cache are ignored, which decreases
>>> latency at the cost of no coherency between bypassed and normal memory
>>> requests. NOA (noalloc) means that the cache is checked and can give you
>>> cache hits, but misses are not cached and the overall latency is higher. I
>>> don't know what the hw does, but I hope it was misnamed and it really means
>>> bypass because there is no point in doing cache lookups on every memory
>>> request if the driver wants to disable caching to *decrease* latency in the
>>> situations when the cache isn't helping.
>>>
>>> Marek
>>>
>>> On Wed, May 11, 2022 at 2:15 AM Lazar, Lijo <lijo.lazar at amd.com> wrote:
>>>
>>>>
>>>>
>>>> On 5/11/2022 11:36 AM, Christian König wrote:
>>>> > Mhm, it doesn't really bypass MALL. It just doesn't allocate any MALL
>>>> > entries on write.
>>>> >
>>>> > How about AMDGPU_VM_PAGE_NO_MALL ?
>>>>
>>>> One more - AMDGPU_VM_PAGE_LLC_* [ LLC = last level cache, * = some sort
>>>> of attribute which decides LLC behaviour]
>>>>
>>>> Thanks,
>>>> Lijo
>>>>
>>>> >
>>>> > Christian.
>>>> >
>>>> > Am 10.05.22 um 23:21 schrieb Marek Olšák:
>>>> >> A better name would be:
>>>> >> AMDGPU_VM_PAGE_BYPASS_MALL
>>>> >>
>>>> >> Marek
>>>> >>
>>>> >> On Fri, May 6, 2022 at 7:23 AM Christian König
>>>> >> <ckoenig.leichtzumerken at gmail.com> wrote:
>>>> >>
>>>> >> Add the AMDGPU_VM_NOALLOC flag to let userspace control MALL
>>>> >> allocation.
>>>> >>
>>>> >> Only compile tested!
>>>> >>
>>>> >> Signed-off-by: Christian König <christian.koenig at amd.com>
>>>> >> ---
>>>> >> drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c | 2 ++
>>>> >> drivers/gpu/drm/amd/amdgpu/gmc_v10_0.c | 3 +++
>>>> >> drivers/gpu/drm/amd/amdgpu/gmc_v11_0.c | 3 +++
>>>> >> include/uapi/drm/amdgpu_drm.h | 2 ++
>>>> >> 4 files changed, 10 insertions(+)
>>>> >>
>>>> >> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>>>> >> b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>>>> >> index bf97d8f07f57..d8129626581f 100644
>>>> >> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>>>> >> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>>>> >> @@ -650,6 +650,8 @@ uint64_t amdgpu_gem_va_map_flags(struct
>>>> >> amdgpu_device *adev, uint32_t flags)
>>>> >> pte_flag |= AMDGPU_PTE_WRITEABLE;
>>>> >> if (flags & AMDGPU_VM_PAGE_PRT)
>>>> >> pte_flag |= AMDGPU_PTE_PRT;
>>>> >> + if (flags & AMDGPU_VM_PAGE_NOALLOC)
>>>> >> + pte_flag |= AMDGPU_PTE_NOALLOC;
>>>> >>
>>>> >> if (adev->gmc.gmc_funcs->map_mtype)
>>>> >> pte_flag |= amdgpu_gmc_map_mtype(adev,
>>>> >> diff --git a/drivers/gpu/drm/amd/amdgpu/gmc_v10_0.c
>>>> >> b/drivers/gpu/drm/amd/amdgpu/gmc_v10_0.c
>>>> >> index b8c79789e1e4..9077dfccaf3c 100644
>>>> >> --- a/drivers/gpu/drm/amd/amdgpu/gmc_v10_0.c
>>>> >> +++ b/drivers/gpu/drm/amd/amdgpu/gmc_v10_0.c
>>>> >> @@ -613,6 +613,9 @@ static void gmc_v10_0_get_vm_pte(struct
>>>> >> amdgpu_device *adev,
>>>> >> *flags &= ~AMDGPU_PTE_MTYPE_NV10_MASK;
>>>> >> *flags |= (mapping->flags & AMDGPU_PTE_MTYPE_NV10_MASK);
>>>> >>
>>>> >> + *flags &= ~AMDGPU_PTE_NOALLOC;
>>>> >> + *flags |= (mapping->flags & AMDGPU_PTE_NOALLOC);
>>>> >> +
>>>> >> if (mapping->flags & AMDGPU_PTE_PRT) {
>>>> >> *flags |= AMDGPU_PTE_PRT;
>>>> >> *flags |= AMDGPU_PTE_SNOOPED;
>>>> >> diff --git a/drivers/gpu/drm/amd/amdgpu/gmc_v11_0.c
>>>> >> b/drivers/gpu/drm/amd/amdgpu/gmc_v11_0.c
>>>> >> index 8d733eeac556..32ee56adb602 100644
>>>> >> --- a/drivers/gpu/drm/amd/amdgpu/gmc_v11_0.c
>>>> >> +++ b/drivers/gpu/drm/amd/amdgpu/gmc_v11_0.c
>>>> >> @@ -508,6 +508,9 @@ static void gmc_v11_0_get_vm_pte(struct
>>>> >> amdgpu_device *adev,
>>>> >> *flags &= ~AMDGPU_PTE_MTYPE_NV10_MASK;
>>>> >> *flags |= (mapping->flags & AMDGPU_PTE_MTYPE_NV10_MASK);
>>>> >>
>>>> >> + *flags &= ~AMDGPU_PTE_NOALLOC;
>>>> >> + *flags |= (mapping->flags & AMDGPU_PTE_NOALLOC);
>>>> >> +
>>>> >> if (mapping->flags & AMDGPU_PTE_PRT) {
>>>> >> *flags |= AMDGPU_PTE_PRT;
>>>> >> *flags |= AMDGPU_PTE_SNOOPED;
>>>> >> diff --git a/include/uapi/drm/amdgpu_drm.h
>>>> >> b/include/uapi/drm/amdgpu_drm.h
>>>> >> index 57b9d8f0133a..9d71d6330687 100644
>>>> >> --- a/include/uapi/drm/amdgpu_drm.h
>>>> >> +++ b/include/uapi/drm/amdgpu_drm.h
>>>> >> @@ -533,6 +533,8 @@ struct drm_amdgpu_gem_op {
>>>> >> #define AMDGPU_VM_MTYPE_UC (4 << 5)
>>>> >> /* Use Read Write MTYPE instead of default MTYPE */
>>>> >> #define AMDGPU_VM_MTYPE_RW (5 << 5)
>>>> >> +/* don't allocate MALL */
>>>> >> +#define AMDGPU_VM_PAGE_NOALLOC (1 << 9)
>>>> >>
>>>> >> struct drm_amdgpu_gem_va {
>>>> >> /** GEM object handle */
>>>> >> --
>>>> >> 2.25.1
>>>> >>
>>>> >
>>>>
>>>
>>>
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