[PATCH] drm/amdgpu: revert "XGMI pstate switch initial support"
Liu, Shaoyun
Shaoyun.Liu at amd.com
Tue Mar 19 15:42:48 UTC 2019
Thanks Felix .
We did consider to put the logic into bo_add/bo_rmv, but Felix pointed
out the object can be migrate from FB to system memory after allocation
. I also think of put the logic inside amdgpu_vm_bo_update_mapping ,
but seems that function prefer to take the dma address already been
calculated (change that will cause a huge code reorganize) . That's the
reason I put the logic before calling into amdgpu_vm_bo_update_mapping .
As the race condition you described sounds reasonable. let me think
how to fix it .
Regards
shaoyun.liu
On 2019-03-19 9:10 a.m., Kuehling, Felix wrote:
> On 3/19/2019 8:49 AM, Christian König wrote:
>> Yeah, all that is perfectly fine.
>>
>> The problem is Shaoyun didn't put this into the mapping code, but
>> rather into the VM state machine. So this won't work at all (the
>> counter and increment/decrement unbalanced and multiple times).
> We tried to consider all the possible ways that this could go wrong.
> Basically, every time a mapping is updated, we update the is_xgmi state
> and update the counter if it changed. Have you seen the counter become
> unbalanced?
>
>
>> The correct place to add this is amdgpu_vm_bo_add/amdgpu_vm_bo_rmv.
> I think we considered that. The problem is that a BO can be migrated
> between bo_add and bo_rmv. I found that even bo->preferred_domain can
> change with AMDGPU_GEM_OP_SET_PLACEMENT. So you can't reliably know
> whether to increment your counter, and your counter can become
> unbalanced if a migration or AMDGPU_GEM_OP_SET_PLACEMENT happens between
> bo_add and bo_rmv.
>
> Therefore we're trying to check for XGMI mappings every time the mapping
> changes and keep track of the state in amdgpu_bo_va_mapping.
>
>
>> Additional to that the approach with the counter doesn't work because
>> you don't have a lock protecting the hw update itself. E.g. while
>> powering down you can add a mapping which needs to power it up again
>> and so powering down and powering up race with each other.
> That's a good point.
>
> Regards,
> Felix
>
>
>> Regards,
>> Christian.
>>
>> Am 19.03.19 um 13:42 schrieb Kuehling, Felix:
>>> We discussed a few different approaches before settling on this one.
>>>
>>> Maybe it needs some more background. XGMI links are quite power hungry.
>>> Being able to power them down improves performance for power-limited
>>> workloads that don't need XGMI. In machine learning, pretty much all
>>> workloads are power limited on our GPUs, so this is not just a
>>> theoretical thing. The problem is, how do you know whether you need
>>> XGMI? You need to know whether there are P2P memory mappings involving
>>> XGMI. So the natural place to put that is in the memory mapping code.
>>>
>>> If you do spot a race condition in the code, let's talk about how to
>>> fix it.
>>>
>>> Regards,
>>> Felix
>>>
>>> On 3/19/2019 8:07 AM, Christian König wrote:
>>>> This reverts commit c9115f8904eef0f880d3b4f8306f553b1bb1c532.
>>>>
>>>> Adding this to the mapping is complete nonsense and the whole
>>>> implementation looks racy. This patch wasn't thoughtfully reviewed
>>>> and should be reverted for now.
>>>>
>>>> Signed-off-by: Christian König <christian.koenig at amd.com>
>>>> ---
>>>> drivers/gpu/drm/amd/amdgpu/amdgpu.h | 3 ---
>>>> drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 3 ---
>>>> drivers/gpu/drm/amd/amdgpu/amdgpu_object.h | 1 -
>>>> drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 29
>>>> +---------------------
>>>> drivers/gpu/drm/amd/amdgpu/amdgpu_xgmi.c | 15 -----------
>>>> drivers/gpu/drm/amd/amdgpu/amdgpu_xgmi.h | 2 --
>>>> 6 files changed, 1 insertion(+), 52 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
>>>> b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
>>>> index b5720c1610e1..1db192150532 100644
>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
>>>> @@ -931,9 +931,6 @@ struct amdgpu_device {
>>>> int asic_reset_res;
>>>> struct work_struct xgmi_reset_work;
>>>> - /* counter of mapped memory through xgmi */
>>>> - atomic_t xgmi_map_counter;
>>>> -
>>>> bool in_baco_reset;
>>>> };
>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
>>>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
>>>> index 964a4d3f1f43..206583707124 100644
>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
>>>> @@ -2018,9 +2018,6 @@ static void
>>>> amdgpu_device_ip_late_init_func_handler(struct work_struct *work)
>>>> r = amdgpu_device_enable_mgpu_fan_boost();
>>>> if (r)
>>>> DRM_ERROR("enable mgpu fan boost failed (%d).\n", r);
>>>> -
>>>> - /*set to low pstate by default */
>>>> - amdgpu_xgmi_set_pstate(adev, 0);
>>>> }
>>>> static void amdgpu_device_delay_enable_gfx_off(struct
>>>> work_struct *work)
>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.h
>>>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.h
>>>> index 6f176bbe4cf2..220a6a7b1bc1 100644
>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.h
>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.h
>>>> @@ -54,7 +54,6 @@ struct amdgpu_bo_va_mapping {
>>>> uint64_t __subtree_last;
>>>> uint64_t offset;
>>>> uint64_t flags;
>>>> - bool is_xgmi;
>>>> };
>>>> /* User space allocated BO in a VM */
>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>>>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>>>> index c5230a9fb7f6..c8f0e4ca05fb 100644
>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>>>> @@ -34,7 +34,6 @@
>>>> #include "amdgpu_trace.h"
>>>> #include "amdgpu_amdkfd.h"
>>>> #include "amdgpu_gmc.h"
>>>> -#include "amdgpu_xgmi.h"
>>>> /**
>>>> * DOC: GPUVM
>>>> @@ -2022,9 +2021,8 @@ int amdgpu_vm_bo_update(struct amdgpu_device
>>>> *adev,
>>>> struct ttm_mem_reg *mem;
>>>> struct drm_mm_node *nodes;
>>>> struct dma_fence *exclusive, **last_update;
>>>> - struct amdgpu_device *bo_adev = adev;
>>>> - bool is_xgmi = false;
>>>> uint64_t flags;
>>>> + struct amdgpu_device *bo_adev = adev;
>>>> int r;
>>>> if (clear || !bo) {
>>>> @@ -2046,10 +2044,6 @@ int amdgpu_vm_bo_update(struct amdgpu_device
>>>> *adev,
>>>> if (bo) {
>>>> flags = amdgpu_ttm_tt_pte_flags(adev, bo->tbo.ttm, mem);
>>>> bo_adev = amdgpu_ttm_adev(bo->tbo.bdev);
>>>> - if (adev != bo_adev &&
>>>> - adev->gmc.xgmi.hive_id &&
>>>> - adev->gmc.xgmi.hive_id == bo_adev->gmc.xgmi.hive_id)
>>>> - is_xgmi = true;
>>>> } else {
>>>> flags = 0x0;
>>>> }
>>>> @@ -2068,19 +2062,6 @@ int amdgpu_vm_bo_update(struct amdgpu_device
>>>> *adev,
>>>> }
>>>> list_for_each_entry(mapping, &bo_va->invalids, list) {
>>>> - if (mapping->is_xgmi != is_xgmi) {
>>>> - if (is_xgmi) {
>>>> - /* Adding an XGMI mapping to the PT */
>>>> - if (atomic_inc_return(&adev->xgmi_map_counter) == 1)
>>>> - amdgpu_xgmi_set_pstate(adev, 1);
>>>> - } else {
>>>> - /* Removing an XGMI mapping from the PT */
>>>> - if (atomic_dec_return(&adev->xgmi_map_counter) == 0)
>>>> - amdgpu_xgmi_set_pstate(adev, 0);
>>>> - }
>>>> - mapping->is_xgmi = is_xgmi;
>>>> - }
>>>> -
>>>> r = amdgpu_vm_bo_split_mapping(adev, exclusive,
>>>> pages_addr, vm,
>>>> mapping, flags, bo_adev, nodes,
>>>> last_update);
>>>> @@ -2298,13 +2279,6 @@ int amdgpu_vm_clear_freed(struct
>>>> amdgpu_device *adev,
>>>> r = amdgpu_vm_bo_update_mapping(adev, NULL, NULL, vm,
>>>> mapping->start, mapping->last,
>>>> init_pte_value, 0, &f);
>>>> -
>>>> - if (mapping->is_xgmi) {
>>>> - /* Removing an XGMI mapping from the PT */
>>>> - if (atomic_dec_return(&adev->xgmi_map_counter) == 0)
>>>> - amdgpu_xgmi_set_pstate(adev, 0);
>>>> - }
>>>> -
>>>> amdgpu_vm_free_mapping(adev, vm, mapping, f);
>>>> if (r) {
>>>> dma_fence_put(f);
>>>> @@ -2501,7 +2475,6 @@ int amdgpu_vm_bo_map(struct amdgpu_device *adev,
>>>> mapping->last = eaddr;
>>>> mapping->offset = offset;
>>>> mapping->flags = flags;
>>>> - mapping->is_xgmi = false;
>>>> amdgpu_vm_bo_insert_map(adev, bo_va, mapping);
>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_xgmi.c
>>>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_xgmi.c
>>>> index 807440d3edff..fcc4b05c745c 100644
>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_xgmi.c
>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_xgmi.c
>>>> @@ -200,7 +200,6 @@ struct amdgpu_hive_info
>>>> *amdgpu_get_xgmi_hive(struct amdgpu_device *adev, int lo
>>>> if (lock)
>>>> mutex_lock(&tmp->hive_lock);
>>>> - tmp->pstate = -1;
>>>> mutex_unlock(&xgmi_mutex);
>>>> @@ -322,17 +321,3 @@ void amdgpu_xgmi_remove_device(struct
>>>> amdgpu_device *adev)
>>>> mutex_unlock(&hive->hive_lock);
>>>> }
>>>> }
>>>> -
>>>> -int amdgpu_xgmi_set_pstate(struct amdgpu_device *adev, int pstate)
>>>> -{
>>>> - int ret = 0;
>>>> - struct amdgpu_hive_info *hive = amdgpu_get_xgmi_hive(adev, 0);
>>>> -
>>>> - if (!hive)
>>>> - return 0;
>>>> -
>>>> - if (hive->pstate == pstate)
>>>> - return 0;
>>>> - /* Todo : sent the message to SMU for pstate change */
>>>> - return ret;
>>>> -}
>>>> \ No newline at end of file
>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_xgmi.h
>>>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_xgmi.h
>>>> index 7e1710fcbef2..24a3b0362f98 100644
>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_xgmi.h
>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_xgmi.h
>>>> @@ -33,13 +33,11 @@ struct amdgpu_hive_info {
>>>> struct kobject *kobj;
>>>> struct device_attribute dev_attr;
>>>> struct amdgpu_device *adev;
>>>> - int pstate; /*0 -- low , 1 -- high , -1 unknown*/
>>>> };
>>>> struct amdgpu_hive_info *amdgpu_get_xgmi_hive(struct
>>>> amdgpu_device *adev, int lock);
>>>> int amdgpu_xgmi_update_topology(struct amdgpu_hive_info *hive,
>>>> struct amdgpu_device *adev);
>>>> int amdgpu_xgmi_add_device(struct amdgpu_device *adev);
>>>> void amdgpu_xgmi_remove_device(struct amdgpu_device *adev);
>>>> -int amdgpu_xgmi_set_pstate(struct amdgpu_device *adev, int pstate);
>>>> #endif
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