Re: [RFC PATCH] drm/ttm: Allow the driver to resolve a WW transaction rollback

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Am 25.05.23 um 14:59 schrieb Thomas Hellström:
On Fri, 2023-05-05 at 16:17 +0200, Thomas Hellström wrote:
Allow drivers to resolve a WW transaction rollback. This allows for
1) Putting a lower-priority transaction to sleep allowing another to
succeed instead both fighting using trylocks.
2) Letting the driver know whether a received -ENOMEM is the result
of
competition with another WW transaction, which can be resolved using
rollback and retry or a real -ENOMEM which should be propagated back
to user-space as a failure.

Signed-off-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
Christian, Any objections?

General idea sounds like what I had in mind as well, but I've moved both my office and household in the last two weeks and are now digging through >800 unread mails/patches.

Give me some days to catch up and I can take a detailed look.

Christian.


/Thomas


---
  drivers/gpu/drm/ttm/ttm_bo.c | 17 +++++++++++++++--
  include/drm/ttm/ttm_bo.h     |  2 ++
  2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo.c
b/drivers/gpu/drm/ttm/ttm_bo.c
index bd5dae4d1624..c3ccbea2be3e 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -561,6 +561,10 @@ static int ttm_mem_evict_wait_busy(struct
ttm_buffer_object *busy_bo,
         if (!busy_bo || !ticket)
                 return -EBUSY;
+       /* We want to resolve contention before trying to lock again.
*/
+       if (ctx->propagate_edeadlk && ctx->contended_bo)
+               return  -EDEADLK;
+
         if (ctx->interruptible)
                 r = dma_resv_lock_interruptible(busy_bo->base.resv,
                                                           ticket);
@@ -575,7 +579,15 @@ static int ttm_mem_evict_wait_busy(struct
ttm_buffer_object *busy_bo,
         if (!r)
                 dma_resv_unlock(busy_bo->base.resv);
-       return r == -EDEADLK ? -EBUSY : r;
+       if (r == -EDEADLK) {
+               if (ctx->propagate_edeadlk) {
+                       ttm_bo_get(busy_bo);
+                       ctx->contended_bo = busy_bo;
+               }
+               r = -EBUSY;
+       }
+
+       return r;
  }
 int ttm_mem_evict_first(struct ttm_device *bdev,
@@ -816,7 +828,7 @@ int ttm_bo_mem_space(struct ttm_buffer_object
*bo,
                         goto error;
         }
-       ret = -ENOMEM;
+       ret = (ctx->propagate_edeadlk && ctx->contended_bo) ? -
EDEADLK : -ENOMEM;
         if (!type_found) {
                 pr_err(TTM_PFX "No compatible memory type found\n");
                 ret = -EINVAL;
@@ -913,6 +925,7 @@ int ttm_bo_validate(struct ttm_buffer_object *bo,
                 if (ret)
                         return ret;
         }
+
         return 0;
  }
  EXPORT_SYMBOL(ttm_bo_validate);
diff --git a/include/drm/ttm/ttm_bo.h b/include/drm/ttm/ttm_bo.h
index 8b113c384236..d8e35a794ce5 100644
--- a/include/drm/ttm/ttm_bo.h
+++ b/include/drm/ttm/ttm_bo.h
@@ -181,8 +181,10 @@ struct ttm_operation_ctx {
         bool gfp_retry_mayfail;
         bool allow_res_evict;
         bool force_alloc;
+       bool propagate_edeadlk;
         struct dma_resv *resv;
         uint64_t bytes_moved;
+       struct ttm_buffer_object *contended_bo;
  };
 /**




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