Am 2021-08-11 um 10:35 a.m. schrieb Philip Yang:
> For xnack on, if range ACCESS or ACCESS_IN_PLACE (AIP) by single GPU, or
> range is ACCESS_IN_PLACE by mGPUs and all mGPUs connection on XGMI same
> hive, the best prefetch location is prefetch_loc GPU. Otherwise, the best
> prefetch location is always CPU because GPU does not have coherent
> mapping VRAM of other GPUs even with large-BAR PCIe connection.
>
> Signed-off-by: Philip Yang <Philip.Yang@xxxxxxx>
Reviewed-by: Felix Kuehling <Felix.Kuehling@xxxxxxx>
> ---
> drivers/gpu/drm/amd/amdkfd/kfd_svm.c | 35 +++++++++++++++-------------
> 1 file changed, 19 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
> index f811a3a24cd2..4cdca8604d69 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
> @@ -2719,22 +2719,26 @@ svm_range_add(struct kfd_process *p, uint64_t start, uint64_t size,
> return 0;
> }
>
> -/* svm_range_best_prefetch_location - decide the best prefetch location
> +/**
> + * svm_range_best_prefetch_location - decide the best prefetch location
> * @prange: svm range structure
> *
> * For xnack off:
> - * If range map to single GPU, the best acutal location is prefetch loc, which
> + * If range map to single GPU, the best prefetch location is prefetch_loc, which
> * can be CPU or GPU.
> *
> - * If range map to multiple GPUs, only if mGPU connection on xgmi same hive,
> - * the best actual location could be prefetch_loc GPU. If mGPU connection on
> - * PCIe, the best actual location is always CPU, because GPU cannot access vram
> - * of other GPUs, assuming PCIe small bar (large bar support is not upstream).
> + * If range is ACCESS or ACCESS_IN_PLACE by mGPUs, only if mGPU connection on
> + * XGMI same hive, the best prefetch location is prefetch_loc GPU, othervise
> + * the best prefetch location is always CPU, because GPU can not have coherent
> + * mapping VRAM of other GPUs even with large-BAR PCIe connection.
> *
> * For xnack on:
> - * The best actual location is prefetch location. If mGPU connection on xgmi
> - * same hive, range map to multiple GPUs. Otherwise, the range only map to
> - * actual location GPU. Other GPU access vm fault will trigger migration.
> + * If range is not ACCESS_IN_PLACE by mGPUs, the best prefetch location is
> + * prefetch_loc, other GPU access will generate vm fault and trigger migration.
> + *
> + * If range is ACCESS_IN_PLACE by mGPUs, only if mGPU connection on XGMI same
> + * hive, the best prefetch location is prefetch_loc GPU, otherwise the best
> + * prefetch location is always CPU.
> *
> * Context: Process context
> *
> @@ -2754,11 +2758,6 @@ svm_range_best_prefetch_location(struct svm_range *prange)
>
> p = container_of(prange->svms, struct kfd_process, svms);
>
> - /* xnack on */
> - if (p->xnack_enabled)
> - goto out;
> -
> - /* xnack off */
> if (!best_loc || best_loc == KFD_IOCTL_SVM_LOCATION_UNDEFINED)
> goto out;
>
> @@ -2768,8 +2767,12 @@ svm_range_best_prefetch_location(struct svm_range *prange)
> best_loc = 0;
> goto out;
> }
> - bitmap_or(bitmap, prange->bitmap_access, prange->bitmap_aip,
> - MAX_GPU_INSTANCE);
> +
> + if (p->xnack_enabled)
> + bitmap_copy(bitmap, prange->bitmap_aip, MAX_GPU_INSTANCE);
> + else
> + bitmap_or(bitmap, prange->bitmap_access, prange->bitmap_aip,
> + MAX_GPU_INSTANCE);
>
> for_each_set_bit(gpuidx, bitmap, MAX_GPU_INSTANCE) {
> pdd = kfd_process_device_from_gpuidx(p, gpuidx);
