Perf event array map kernel-side implementation #4144

mikeagun · 2025-01-16T18:42:17Z

Description

Implements the kernel side of perf event array maps.

This includes the core and kernel changes for #658, with part of the user-side API skeleton.

Testing

Includes platform and execution context tests.

Documentation

Documented in code and PerfEventArray.md.

Installation

N/A

include/bpf_helper_defs.h

include/ebpf_api.h

include/ebpf_core_structs.h

include/ebpf_extension.h

libs/api/ebpf_api.cpp

libs/execution_context/ebpf_core.c

libs/runtime/unit/platform_unit_test.cpp

libs/runtime/ebpf_perf_event_array.c

libs/execution_context/ebpf_link.c

mikeagun · 2025-02-12T21:53:28Z

Moving to draft until the ring buffer refactoring is merged in #4204

mikeagun · 2025-02-25T02:24:40Z

This is currently blocked on #4204, as it uses the new ring buffer for wait-free reserve (at dispatch) in the per-cpu rings. Most of the refactoring to use the new ring buffer has been done, but after the new ring buffer implementation is merged I'll update+publish this again.

mikeagun · 2025-03-07T16:33:51Z

I split the context header support requirement out into #4267. After that passes all CICD tests I'll rebase this PR split into two commits - context header support then perf event array impl.

libs/execution_context/ebpf_maps.c

libs/runtime/ebpf_ring_buffer.h

libs/execution_context/ebpf_maps.c

libs/execution_context/ebpf_maps.h

docs/eBpfExtensions.md

docs/PerfEventArray.md

include/ebpf_structs.h

libs/execution_context/ebpf_core.c

libs/execution_context/ebpf_maps.h

libs/execution_context/ebpf_program.h

libs/execution_context/unit/execution_context_unit_test.cpp

saxena-anurag · 2025-03-19T06:18:14Z

libs/execution_context/ebpf_core.c

-    _Inout_ ebpf_operation_ring_buffer_map_async_query_reply_t* reply,
+_ebpf_core_protocol_map_async_query(
+    _In_ const ebpf_operation_map_async_query_request_t* request,
+    //_Inout_updates_bytes_(reply_length) ebpf_operation_map_async_query_reply_t* reply,


nit: delete commented code.

Fixed in #4300

saxena-anurag · 2025-03-21T16:37:49Z

libs/api/api_internal.h

+ * @brief Subscribe for notifications from the input perf event array map.
+ *
+ * @param[in] perf_event_array_map_fd File descriptor to the perf event array map.
+ * @param[in, out] sample_callback_context Pointer to supplied context to be passed in notification callback.


Suggested change

* @param[in, out] sample_callback_context Pointer to supplied context to be passed in notification callback.

* @param[in, out] callback_context Pointer to supplied context to be passed in notification callback.

Fixed in #4300

saxena-anurag · 2025-03-21T23:01:28Z

libs/api/ebpf_api.cpp

+          async_ioctl_completion(nullptr), async_ioctl_failed(false)
+    {
+    }
+    ~_ebpf_perf_event_array_subscription() { EBPF_LOG_ENTRY(); }


nit: normally ENTRY and EXIT traces should be paired.

Fixed in #4300

saxena-anurag · 2025-03-22T03:01:43Z

libs/execution_context/ebpf_program.c

@@ -2688,3 +2696,40 @@ ebpf_program_set_flags(_Inout_ ebpf_program_t* program, uint64_t flags)
 {
    program->flags = flags;
 }
+
+void
+ebpf_program_set_header_context_descriptor(


this is invoked only from ebpf_program.c. Should this be marked static?

saxena-anurag · 2025-03-22T03:02:34Z

libs/execution_context/ebpf_program.c

+}
+
+void
+ebpf_program_get_header_context_descriptor(


same as earlier -- invoked only from ebpf_program.c. Should this be marked static?

saxena-anurag · 2025-03-22T03:24:57Z

libs/api/ebpf_api.cpp

+        size_t perf_event_array_size = 0;
+        uint32_t dummy;
+
+        result = _get_map_descriptor_properties(


is it possible to cache the map descriptor in ebpf_perf_event_array_subscription_t to avoid a possible IOCTL call to get map properties each time?

saxena-anurag · 2025-03-22T03:49:35Z

libs/execution_context/ebpf_maps.c

+{
+    ebpf_core_map_t core_map;
+    uint32_t ring_count;
+    // Flag that is set the first time an async operation is queued to the map.


nit: which flag is this?

This was for the tripwire flag which has been moved into a shared struct. Fixed in #4300.

saxena-anurag · 2025-03-22T04:45:42Z

libs/execution_context/ebpf_maps.c

+        EBPF_FROM_FIELD(ebpf_core_perf_event_array_map_t, core_map, map);
+    uint32_t cpu_id = (uint32_t)index;
+    ebpf_assert(cpu_id < perf_event_array_map->ring_count);
+    ebpf_core_perf_ring_t* ring = &perf_event_array_map->rings[cpu_id];


Do we need to handle CPU hot-add case here? Or at least fail the call if cpu_id > perf_event_array_map->ring_count?

I added a runtime check of the cpu_id in #4300.

Currently we allocate rings for the maximum logical processor count -- so hot add CPUs will already get rings allocated during initialization.

This was an issue for epoch memory because all CPUs participating in epochs need to participate in the consensus protocol. For perf array, a hot-add CPU that never gets added is functionally equivalent to a CPU that existed at boot but never has records queued to it.

saxena-anurag · 2025-03-22T04:47:36Z

libs/execution_context/ebpf_maps.c

+
+    ebpf_core_perf_event_array_map_t* perf_event_array_map =
+        EBPF_FROM_FIELD(ebpf_core_perf_event_array_map_t, core_map, map);
+    ebpf_core_perf_ring_t* ring = &perf_event_array_map->rings[cpu_id];


same as above.

See above answer.

saxena-anurag · 2025-03-22T04:53:06Z

libs/execution_context/ebpf_maps.c

+    if (irql_at_enter < DISPATCH_LEVEL) {
+        ebpf_lower_irql(irql_at_enter);
+    }
+ExitPreDispatch:


nit: snake_case.

Fixed in #4300.

saxena-anurag

Approved, modulo some comments.

mikeagun force-pushed the perfbuf-impl branch from 7623a4f to 10d4f86 Compare January 18, 2025 02:23

mikeagun mentioned this pull request Jan 27, 2025

Support direct mapped memory consumers for ring buffer and perf event array maps #4163

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mikeagun force-pushed the perfbuf-impl branch from d5f2cea to a5f9711 Compare January 29, 2025 17:41

mikeagun marked this pull request as ready for review February 4, 2025 19:58

mikeagun requested review from dthaler, poornagmsft, Alan-Jowett, saxena-anurag, shankarseal, dv-msft, matthewige and mtfriesen as code owners February 4, 2025 19:58

mikeagun changed the title ~~DRAFT Perf event array map implementation.~~ Perf event array map kernel-side implementation. Feb 4, 2025

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mikeagun marked this pull request as draft February 12, 2025 21:54

mikeagun mentioned this pull request Feb 26, 2025

Design proposal for new ring buffer API #3848

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mikeagun force-pushed the perfbuf-impl branch from 6513f71 to 547a6e1 Compare February 28, 2025 17:30

mikeagun marked this pull request as ready for review February 28, 2025 17:38

mikeagun requested review from LakshK98 and vpidatala94 as code owners February 28, 2025 17:38

mikeagun mentioned this pull request Mar 7, 2025

Make context header support mandatory #4267

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mikeagun force-pushed the perfbuf-impl branch from dc44759 to 10b8ee7 Compare March 7, 2025 18:15

mikeagun changed the title ~~Perf event array map kernel-side implementation.~~ Perf event array map kernel-side implementation Mar 7, 2025

mikeagun commented Mar 19, 2025

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Feedback and unit tests.

19b7f7b

mikeagun dismissed shankarseal’s stale review via 19b7f7b March 21, 2025 17:15

mikeagun mentioned this pull request Mar 21, 2025

Make ebpf_ring_buffer_t struct opaque #4289

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Add issue to make ringbuf struct opaque.

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mikeagun requested review from dthaler, saxena-anurag and shankarseal March 21, 2025 18:45

mikeagun and others added 3 commits March 21, 2025 12:03

Merge branch 'main' into perfbuf-impl

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analyze fix and call-out to output when no capture

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fix result check in output

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Merged via the queue into microsoft:main with commit 2465eef Mar 23, 2025
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mikeagun mentioned this pull request Mar 24, 2025

Perf event array cleanup. #4300

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Perf event array map kernel-side implementation #4144

Perf event array map kernel-side implementation #4144

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	* @param[in, out] sample_callback_context Pointer to supplied context to be passed in notification callback.
	* @param[in, out] callback_context Pointer to supplied context to be passed in notification callback.

Perf event array map kernel-side implementation #4144

Perf event array map kernel-side implementation #4144

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mikeagun commented Jan 16, 2025 • edited Loading

Description

Testing

Documentation

Installation

mikeagun commented Feb 12, 2025

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mikeagun commented Jan 16, 2025 •

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