[metal] Increase MAX_COMMAND_BUFFERS (#7858)

Author: andyleiserson

cts_runner/test.lst

@@ -5,6 +5,8 @@ webgpu:api,operation,compute,basic:memcpy:*
 //FAIL: webgpu:api,operation,compute,basic:large_dispatch:*
 webgpu:api,operation,compute_pipeline,overrides:*
 webgpu:api,operation,device,lost:*
+webgpu:api,validation,encoding,beginComputePass:*
+webgpu:api,validation,encoding,beginRenderPass:*
 webgpu:api,validation,encoding,cmds,clearBuffer:*
 webgpu:api,validation,encoding,cmds,compute_pass:set_pipeline:*
 webgpu:api,validation,encoding,cmds,compute_pass:dispatch_sizes:*
@@ -31,13 +33,22 @@ webgpu:api,validation,encoding,encoder_open_state:render_pass_commands:*
 //FAIL: webgpu:api,validation,encoding,encoder_open_state:render_bundle_commands:*
 // https://github.com/gfx-rs/wgpu/issues/7857
 webgpu:api,validation,encoding,encoder_open_state:compute_pass_commands:*
-webgpu:api,validation,encoding,beginComputePass:*
-webgpu:api,validation,encoding,beginRenderPass:*
+webgpu:api,validation,encoding,programmable,pipeline_bind_group_compat:bgl_binding_mismatch:encoderType="compute%20pass";*
+webgpu:api,validation,encoding,programmable,pipeline_bind_group_compat:bgl_binding_mismatch:encoderType="render%20pass";*
+webgpu:api,validation,encoding,programmable,pipeline_bind_group_compat:bgl_resource_type_mismatch:encoderType="compute%20pass";*
+webgpu:api,validation,encoding,programmable,pipeline_bind_group_compat:bgl_resource_type_mismatch:encoderType="render%20pass";*
+webgpu:api,validation,encoding,programmable,pipeline_bind_group_compat:bgl_visibility_mismatch:encoderType="compute%20pass";*
+webgpu:api,validation,encoding,programmable,pipeline_bind_group_compat:bgl_visibility_mismatch:encoderType="render%20pass";*
+webgpu:api,validation,encoding,programmable,pipeline_bind_group_compat:bind_groups_and_pipeline_layout_mismatch:encoderType="compute%20pass";*
+webgpu:api,validation,encoding,programmable,pipeline_bind_group_compat:bind_groups_and_pipeline_layout_mismatch:encoderType="render%20pass";*
+webgpu:api,validation,encoding,programmable,pipeline_bind_group_compat:buffer_binding,render_pipeline:*
+webgpu:api,validation,encoding,programmable,pipeline_bind_group_compat:sampler_binding,render_pipeline:*
 webgpu:api,validation,queue,submit:command_buffer,device_mismatch:*
 webgpu:api,validation,queue,submit:command_buffer,duplicate_buffers:*
 webgpu:api,validation,queue,submit:command_buffer,submit_invalidates:*
 //FAIL: webgpu:api,validation,queue,submit:command_buffer,invalid_submit_invalidates:*
 // https://github.com/gfx-rs/wgpu/issues/3911#issuecomment-2972995675
+webgpu:api,validation,render_pass,render_pass_descriptor:attachments,*
 webgpu:api,operation,render_pipeline,overrides:*
 webgpu:api,operation,rendering,basic:clear:*
 webgpu:api,operation,rendering,basic:fullscreen_quad:*

wgpu-hal/src/metal/adapter.rs

@@ -10,7 +10,24 @@ use alloc::sync::Arc;
 
 use super::TimestampQuerySupport;
 
-const MAX_COMMAND_BUFFERS: u64 = 2048;
+/// Maximum number of command buffers for `MTLCommandQueue`s that we create.
+///
+/// If a [new command buffer] is requested when Metal has run out of command
+/// buffers, it waits indefinitely for one to become available. If the
+/// outstanding command buffers are actively executing on the GPU, this will
+/// happen relatively quickly. But if the outstanding command buffers will only
+/// be recovered upon GC, and attempting to get a new command buffer prevents
+/// forward progress towards that GC, there is a deadlock.
+///
+/// This is mostly a problem for the CTS, which frequently creates command
+/// buffers that it does not submit. It is unclear how likely command buffer
+/// exhaustion is in real applications.
+///
+/// This limit was increased from a previous value of 2048 for
+/// <https://bugzilla.mozilla.org/show_bug.cgi?id=1971452>.
+///
+/// [new command buffer]: https://developer.apple.com/documentation/metal/mtlcommandqueue/makecommandbuffer()?language=objc
+const MAX_COMMAND_BUFFERS: u64 = 4096;
 
 unsafe impl Send for super::Adapter {}
 unsafe impl Sync for super::Adapter {}