From c591c9d6a6a4ccdf463dd45e0359ef401566edf8 Mon Sep 17 00:00:00 2001
From: Willy Tarreau <w@1wt.eu>
Date: Thu, 27 Feb 2025 10:59:10 +0100
Subject: [PATCH] MINOR: cpu-topo: add "only-thread" and "drop-thread" to
 cpu-set

These are processed after the topology is detected, and they allow to
restrict binding to or evict CPUs matching the indicated hardware
thread number(s). It can be used to reserve even threads for HW IRQs
and odd threads for haproxy for example, or to evict efficient cores
that do only have thread #0.
---
 doc/configuration.txt |  2 ++
 src/cpu_topo.c        | 31 ++++++++++++++++++++++++++++++-
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/doc/configuration.txt b/doc/configuration.txt
index 7cd4c30ba..7a90a60cb 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -1957,6 +1957,8 @@ cpu-set <directive>...
     - only-cpu <set>     do not bind to CPUs not in this set
     - drop-node <set>    do not bind to CPUs belonging to this NUMA node
     - only-node <set>    do not bind to CPUs not belonging to this NUMA node
+    - drop-thread <set>  do not bind to CPUs on this hardware thread number
+    - only-thread <set>  do not bind to CPUs on other hardware thread number
 
 crt-base <dir>
   Assigns a default directory to fetch SSL certificates from when a relative
diff --git a/src/cpu_topo.c b/src/cpu_topo.c
index e976432fc..5af131e1e 100644
--- a/src/cpu_topo.c
+++ b/src/cpu_topo.c
@@ -35,6 +35,9 @@ struct cpu_set_cfg {
 	/* node numbers to accept / reject */
 	struct hap_cpuset only_nodes;
 	struct hap_cpuset drop_nodes;
+	/* thread numbers to accept / reject */
+	struct hap_cpuset only_threads;
+	struct hap_cpuset drop_threads;
 } cpu_set_cfg;
 
 /* Detects CPUs that are online on the system. It may rely on FS access (e.g.
@@ -840,6 +843,13 @@ void cpu_refine_cpusets(void)
 		    !ha_cpuset_isset(&cpu_set_cfg.only_nodes, ha_cpu_topo[cpu].no_id))
 			ha_cpu_topo[cpu].st |= HA_CPU_F_DONT_USE;
 	}
+
+	/* remove CPUs in the drop-thread set or not in the only-thread set */
+	for (cpu = 0; cpu <= cpu_topo_lastcpu; cpu++) {
+		if ( ha_cpuset_isset(&cpu_set_cfg.drop_threads, ha_cpu_topo[cpu].th_id) ||
+		    !ha_cpuset_isset(&cpu_set_cfg.only_threads, ha_cpu_topo[cpu].th_id))
+			ha_cpu_topo[cpu].st |= HA_CPU_F_DONT_USE;
+	}
 }
 
 /* CPU topology detection below, OS-specific */
@@ -1223,6 +1233,22 @@ static int cfg_parse_cpu_set(char **args, int section_type, struct proxy *curpx,
 				ha_cpuset_and(&cpu_set_cfg.only_nodes, &tmp_cpuset);
 			arg++;
 		}
+		else if (strcmp(args[arg], "drop-thread") == 0 || strcmp(args[arg], "only-thread") == 0) {
+			if (!*args[arg + 1]) {
+				memprintf(err, "missing thread set");
+				goto parse_err;
+			}
+
+			cpu_set_str[0] = args[arg + 1];
+			if (parse_cpu_set(cpu_set_str, &tmp_cpuset, err) != 0)
+				goto parse_err;
+
+			if (*args[arg] == 'd') // threads to drop
+				ha_cpuset_or(&cpu_set_cfg.drop_threads, &tmp_cpuset);
+			else // threads to keep
+				ha_cpuset_and(&cpu_set_cfg.only_threads, &tmp_cpuset);
+			arg++;
+		}
 		else {
 			/* fall back with default error message */
 			memprintf(err, "'%s' passed an unknown directive '%s'", args[0], args[arg]);
@@ -1247,7 +1273,7 @@ static int cfg_parse_cpu_set(char **args, int section_type, struct proxy *curpx,
 
  leave_with_err:
 	/* complete with supported directives */
-	memprintf(err, "%s (only 'reset', 'only-cpu', 'drop-cpu', 'only-node', 'drop-node' supported).", *err);
+	memprintf(err, "%s (only 'reset', 'only-cpu', 'drop-cpu', 'only-node', 'drop-node', 'only-thread', 'drop-thread' supported).", *err);
  leave:
 	return -1;
 }
@@ -1294,11 +1320,14 @@ static int cpu_topo_alloc(void)
 	ha_cpuset_zero(&cpu_set_cfg.only_cpus);
 	ha_cpuset_zero(&cpu_set_cfg.drop_nodes);
 	ha_cpuset_zero(&cpu_set_cfg.only_nodes);
+	ha_cpuset_zero(&cpu_set_cfg.drop_threads);
+	ha_cpuset_zero(&cpu_set_cfg.only_threads);
 
 	/* preset all CPUs in the "only-XXX" sets */
 	for (cpu = 0; cpu < cpu_topo_maxcpus; cpu++) {
 		ha_cpuset_set(&cpu_set_cfg.only_cpus, cpu);
 		ha_cpuset_set(&cpu_set_cfg.only_nodes, cpu);
+		ha_cpuset_set(&cpu_set_cfg.only_threads, cpu);
 	}
 
 	return 1;