Metal: Resolve race condition when releasing large numbers of buffers simultaneously. #104687

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Jason Fielder wants to merge 1 commits from Jason-Fielder/blender:MetalSafeFreeList_FixAndOptimise_3 into main

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Race condition if several competing threads are inserting Metal buffers into the MTLSafeFreList simultaneously while a new list chunk is being created.

Also raise the limit for an MTLSafeFreeListChunk size to optimise for interactivity when releasing lots of memory simultaneously.

Authored by Apple: Michael Parkin-White

Related to #96261

Race condition if several competing threads are inserting Metal buffers into the MTLSafeFreList simultaneously while a new list chunk is being created. Also raise the limit for an MTLSafeFreeListChunk size to optimise for interactivity when releasing lots of memory simultaneously. Authored by Apple: Michael Parkin-White Related to #96261
Jason Fielder added 1 commit 2023-02-13 12:04:57 +01:00
b78c1ced59 Metal: Resolve race condition when releasing large numbers of buffers simultaneously.
Race condition if several competing threads are inserting Metal buffers into the MTLSafeFreList simultaneously while a new list chunk is being created.

Also raise the limit for an MTLSafeFreeListChunk size to optimise for interactivity when releasing lots of memory simultaneously.

Authored by Apple: Michael Parkin-White

Related to #96261
Jason Fielder requested review from Clément Foucault 2023-02-13 12:05:23 +01:00
Brecht Van Lommel added this to the EEVEE & Viewport project 2023-02-13 12:13:07 +01:00
Clément Foucault reviewed 2023-02-13 23:22:09 +01:00
@ -414,1 +413,4 @@
/* Check if first caller to generate next pool in chain.
* Otherwise, ensure pool exists or wait for first caller to create next pool. */
MTLSafeFreeList *next_list = nullptr;
int has_next = has_next_pool_++;

I didn't catch that first but has_next_pool_ is basically the list length. Might be worth renaming the variable.

I didn't catch that first but `has_next_pool_` is basically the list length. Might be worth renaming the variable.
@ -417,0 +425,4 @@
* Another thread will be creating the next link in the chain and will hold the lock
* so if the resource is not ready, we can hold until it is available. */
while ((next_list = next_.load()) == nullptr) {
/* Apply local lock to efficiently stall waiting thread on new safelist block link creaton.

creaton. typo

`creaton.` typo
@ -417,0 +426,4 @@
* so if the resource is not ready, we can hold until it is available. */
while ((next_list = next_.load()) == nullptr) {
/* Apply local lock to efficiently stall waiting thread on new safelist block link creaton.
* This lock and loop will complete quickly. */

I have to admit I'm a bit doubtful about what's the intent here. Is the lock thing inside the loop supposed to just slow down the waiting thread and avoid high CPU usage? This does feel hacky anyway.

I have to admit I'm a bit doubtful about what's the intent here. Is the lock thing inside the loop supposed to just slow down the waiting thread and avoid high CPU usage? This does feel hacky anyway.

#105254 replace this PR. Closing.

#105254 replace this PR. Closing.

Pull request closed

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Reference: blender/blender#104687
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