Fix breakdown model forbidden value 0 error

When a event causes a new value in the sort module, the first time it
will write all output values, which most of them will be zero. Writting
a zero value is forbidden by default, so we relax the constraint with
the PRV_ZERO flag.

CHANGELOG.md

@@ -7,6 +7,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- Fix breakdown model error that was preventing a zero value to be written in
+  the PRV trace.
+
 ## [1.9.0] - 2024-04-25
 
 ### Added

src/emu/nanos6/breakdown.c

@@ -1,4 +1,4 @@
-/* Copyright (c) 2023 Barcelona Supercomputing Center (BSC)
+/* Copyright (c) 2023-2024 Barcelona Supercomputing Center (BSC)
  * SPDX-License-Identifier: GPL-3.0-or-later */
 
 #include "breakdown.h"
@@ -239,6 +239,11 @@ model_nanos6_breakdown_connect(struct emu *emu)
 		long type = PRV_NANOS6_BREAKDOWN;
 		long flags = PRV_SKIPDUP;
 
+		/* We may emit zero at the start, when an input changes and all
+		 * the other sort output channels write a zero in the output,
+		 * before the last value is set in prv.c. */
+		flags |= PRV_ZERO;
+
 		struct chan *out = sort_get_output(&bemu->sort, i);
 		if (prv_register(prv, i, type, bay, out, flags)) {
 			err("prv_register failed");

test/emu/common/instr.h

@@ -1,4 +1,4 @@
-/* Copyright (c) 2021-2023 Barcelona Supercomputing Center (BSC)
+/* Copyright (c) 2021-2024 Barcelona Supercomputing Center (BSC)
  * SPDX-License-Identifier: GPL-3.0-or-later */
 
 #ifndef INSTR_H
@@ -62,6 +62,7 @@ int64_t get_delta(void);
 	}
 
 INSTR_3ARG(instr_thread_execute, "OHx", int32_t, cpu, int32_t, creator_tid, uint64_t, tag)
+INSTR_1ARG(instr_thread_affinity_set, "OAs", int32_t, cpu)
 
 static inline void
 instr_thread_end(void)

test/emu/nanos6/CMakeLists.txt

@@ -1,4 +1,4 @@
-# Copyright (c) 2022-2023 Barcelona Supercomputing Center (BSC)
+# Copyright (c) 2022-2024 Barcelona Supercomputing Center (BSC)
 # SPDX-License-Identifier: GPL-3.0-or-later
 
 test_emu(nested-tasks.c)
@@ -14,5 +14,6 @@ test_emu(switch-same-type.c)
 test_emu(sponge.c)
 test_emu(sponge-breakdown.c BREAKDOWN)
 test_emu(breakdown-no-black.c BREAKDOWN)
+test_emu(breakdown-write-zero.c MP BREAKDOWN)
 test_emu(rerun-task-bad.c SHOULD_FAIL
   REGEX "body_execute: body(id=1,taskid=1) is not allowed to run again")

test/emu/nanos6/breakdown-write-zero.c

@@ -0,0 +1,35 @@
+/* Copyright (c) 2024 Barcelona Supercomputing Center (BSC)
+ * SPDX-License-Identifier: GPL-3.0-or-later */
+
+#include <stdint.h>
+#include <stdlib.h>
+#include "compat.h"
+#include "instr.h"
+#include "instr_nanos6.h"
+
+/* Cause the sort module to write zeros in some rows when the breakdown model is
+ * enabled, which shouldn't cause a panic. */
+int
+main(void)
+{
+	int rank = atoi(getenv("OVNI_RANK"));
+	int nranks = atoi(getenv("OVNI_NRANKS"));
+
+	if (nranks < 2)
+		die("need at least two ranks");
+
+	instr_start(rank, nranks);
+	instr_nanos6_init();
+
+	/* Change the subsystem in a single thread, while the rest remain NULL.
+	 * This shouldn't cause a panic, as writting zero is ok for the other
+	 * sort outputs. */
+	if (rank == 0) {
+		instr_nanos6_worker_loop_enter();
+		instr_nanos6_worker_loop_exit();
+	}
+
+	instr_end();
+
+	return 0;
+}

test/rt/nanos6/CMakeLists.txt

@@ -1,4 +1,4 @@
-# Copyright (c) 2022-2023 Barcelona Supercomputing Center (BSC)
+# Copyright (c) 2022-2024 Barcelona Supercomputing Center (BSC)
 # SPDX-License-Identifier: GPL-3.0-or-later
 
 find_package(Nanos6)
@@ -57,3 +57,8 @@ nanos6_rt_test(spawn-task-external-bad.c SHOULD_FAIL
 nanos6_rt_test(simple-task.c NAME simple-task-level-1 LEVEL 1)
 nanos6_rt_test(simple-task.c NAME simple-task-level-2 LEVEL 2)
 nanos6_rt_test(simple-task.c NAME simple-task-level-3 LEVEL 3)
+
+# Same but with breakdown enabled
+nanos6_rt_test(simple-task.c NAME simple-task-breakdown-level-1 LEVEL 1 BREAKDOWN)
+nanos6_rt_test(simple-task.c NAME simple-task-breakdown-level-2 LEVEL 2 BREAKDOWN)
+nanos6_rt_test(simple-task.c NAME simple-task-breakdown-level-3 LEVEL 3 BREAKDOWN)