Re: [PATCH v3 00/10] Preemption support for A7XX

[Antonino Maniscalco <antomani103@gmail.com>]

On 9/6/24 9:58 PM, Akhil P Oommen wrote:
> On Thu, Sep 05, 2024 at 04:51:18PM +0200, Antonino Maniscalco wrote:
>> This series implements preemption for A7XX targets, which allows the GPU to
>> switch to an higher priority ring when work is pushed to it, reducing latency
>> for high priority submissions.
>>
>> This series enables L1 preemption with skip_save_restore which requires
>> the following userspace patches to function:
>>
>> https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30544
>>
>> A flag is added to `msm_submitqueue_create` to only allow submissions
>> from compatible userspace to be preempted, therefore maintaining
>> compatibility.
>>
>> Preemption is currently only enabled by default on A750, it can be
>> enabled on other targets through the `enable_preemption` module
>> parameter. This is because more testing is required on other targets.
>>
>> For testing on other HW it is sufficient to set that parameter to a
>> value of 1, then using the branch of mesa linked above, `TU_DEBUG=hiprio`
>> allows to run any application as high priority therefore preempting
>> submissions from other applications.
>>
>> The `msm_gpu_preemption_trigger` and `msm_gpu_preemption_irq` traces
>> added in this series can be used to observe preemption's behavior as
>> well as measuring preemption latency.
>>
>> Some commits from this series are based on a previous series to enable
>> preemption on A6XX targets:
>>
>> https://lkml.kernel.org/1520489185-21828-1-git-send-email-smasetty@codeaurora.org
>>
>> Signed-off-by: Antonino Maniscalco <antomani103@gmail.com>
> 
> Antonino, can you please test this once with per-process pt disabled to
> ensure that is not broken? It is handy sometimes while debugging.
> We just need to remove "adreno-smmu" compatible string from gpu smmu
> node in DT.
> 

Removing that from the DT causes a crash inside 
`msm_iommu_pagetable_create` as it seems `create_private_address_space` 
is assigned unconditionally in a6xx_gpu.c . I tested it with the 
following change:

diff --git a/drivers/gpu/drm/msm/msm_gpu.c b/drivers/gpu/drm/msm/msm_gpu.c
index 9e5a83b885f0..4111f5fd9721 100644
--- a/drivers/gpu/drm/msm/msm_gpu.c
+++ b/drivers/gpu/drm/msm/msm_gpu.c
@@ -832,11 +832,11 @@ msm_gpu_create_private_address_space(struct 
msm_gpu *gpu, struct task_struct *ta
          * If the target doesn't support private address spaces then return
          * the global one
          */
-       if (gpu->funcs->create_private_address_space) {
-               aspace = gpu->funcs->create_private_address_space(gpu);
-               if (!IS_ERR(aspace))
-                       aspace->pid = get_pid(task_pid(task));
-       }
+       /* if (gpu->funcs->create_private_address_space) { */
+       /*      aspace = gpu->funcs->create_private_address_space(gpu); */
+       /*      if (!IS_ERR(aspace)) */
+       /*              aspace->pid = get_pid(task_pid(task)); */
+       /* } */

         if (IS_ERR_OR_NULL(aspace))
                 aspace = msm_gem_address_space_get(gpu->aspace);

and it appears to work.

> -Akhil.
> 
>> ---
>> Changes in v3:
>> - Added documentation about preemption
>> - Use quirks to determine which target supports preemption
>> - Add a module parameter to force disabling or enabling preemption
>> - Clear postamble when profiling
>> - Define A6XX_CP_CONTEXT_SWITCH_CNTL_LEVEL fields in a6xx.xml
>> - Make preemption records MAP_PRIV
>> - Removed user ctx record (NON_PRIV) and patch 2/9 as it's not needed
>>    anymore
>> - Link to v2: https://lore.kernel.org/r/20240830-preemption-a750-t-v2-0-86aeead2cd80@gmail.com
>>
>> Changes in v2:
>> - Added preept_record_size for X185 in PATCH 3/7
>> - Added patches to reset perf counters
>> - Dropped unused defines
>> - Dropped unused variable (fixes warning)
>> - Only enable preemption on a750
>> - Reject MSM_SUBMITQUEUE_ALLOW_PREEMPT for unsupported targets
>> - Added Akhil's Reviewed-By tags to patches 1/9,2/9,3/9
>> - Added Neil's Tested-By tags
>> - Added explanation for UAPI changes in commit message
>> - Link to v1: https://lore.kernel.org/r/20240815-preemption-a750-t-v1-0-7bda26c34037@gmail.com
>>
>> ---
>> Antonino Maniscalco (10):
>>        drm/msm: Fix bv_fence being used as bv_rptr
>>        drm/msm: Add a `preempt_record_size` field
>>        drm/msm: Add CONTEXT_SWITCH_CNTL bitfields
>>        drm/msm/A6xx: Implement preemption for A7XX targets
>>        drm/msm/A6xx: Sync relevant adreno_pm4.xml changes
>>        drm/msm/A6xx: Use posamble to reset counters on preemption
>>        drm/msm/A6xx: Add traces for preemption
>>        drm/msm/A6XX: Add a flag to allow preemption to submitqueue_create
>>        drm/msm/A6xx: Enable preemption for A750
>>        Documentation: document adreno preemption
>>
>>   Documentation/gpu/msm-preemption.rst               |  98 +++++
>>   drivers/gpu/drm/msm/Makefile                       |   1 +
>>   drivers/gpu/drm/msm/adreno/a6xx_catalog.c          |   7 +-
>>   drivers/gpu/drm/msm/adreno/a6xx_gpu.c              | 331 +++++++++++++++-
>>   drivers/gpu/drm/msm/adreno/a6xx_gpu.h              | 166 ++++++++
>>   drivers/gpu/drm/msm/adreno/a6xx_preempt.c          | 430 +++++++++++++++++++++
>>   drivers/gpu/drm/msm/adreno/adreno_gpu.h            |   9 +-
>>   drivers/gpu/drm/msm/msm_drv.c                      |   4 +
>>   drivers/gpu/drm/msm/msm_gpu_trace.h                |  28 ++
>>   drivers/gpu/drm/msm/msm_ringbuffer.h               |   8 +
>>   drivers/gpu/drm/msm/msm_submitqueue.c              |   3 +
>>   drivers/gpu/drm/msm/registers/adreno/a6xx.xml      |   7 +-
>>   .../gpu/drm/msm/registers/adreno/adreno_pm4.xml    |  39 +-
>>   include/uapi/drm/msm_drm.h                         |   5 +-
>>   14 files changed, 1094 insertions(+), 42 deletions(-)
>> ---
>> base-commit: 7c626ce4bae1ac14f60076d00eafe71af30450ba
>> change-id: 20240815-preemption-a750-t-fcee9a844b39
>>
>> Best regards,
>> -- 
>> Antonino Maniscalco <antomani103@gmail.com>
>>

Best regards,
-- 
Antonino Maniscalco <antomani103@gmail.com>