git: 5720b8de4832 - main - riscv: Add an hw.ncpu tunable to limit the number of cores

[Jessica Clarke]

The branch main has been updated by jrtc27:

URL: https://cgit.FreeBSD.org/src/commit/?id=5720b8de4832da70e76b9a72c679d0b168d7834e

commit 5720b8de4832da70e76b9a72c679d0b168d7834e
Author:     Jessica Clarke <jrtc27 at FreeBSD.org>
AuthorDate: 2021-06-15 00:21:38 +0000
Commit:     Jessica Clarke <jrtc27 at FreeBSD.org>
CommitDate: 2021-06-15 00:22:13 +0000

    riscv: Add an hw.ncpu tunable to limit the number of cores
    
    Based on a similar change to arm64 in 01a8235ea61c.
    
    Reviewed by:    mhorne
    MRC after:      1 week
    Differential Revision:  https://reviews.freebsd.org/D30655
---
 sys/riscv/riscv/mp_machdep.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/sys/riscv/riscv/mp_machdep.c b/sys/riscv/riscv/mp_machdep.c
index cdcc86e715dd..1dadf19ce51f 100644
--- a/sys/riscv/riscv/mp_machdep.c
+++ b/sys/riscv/riscv/mp_machdep.c
@@ -532,9 +532,9 @@ cpu_check_mmu(u_int id, phandle_t node, u_int addr_size, pcell_t *reg)
 void
 cpu_mp_setmaxid(void)
 {
-#ifdef FDT
 	int cores;
 
+#ifdef FDT
 	cores = ofw_cpu_early_foreach(cpu_check_mmu, true);
 	if (cores > 0) {
 		cores = MIN(cores, MAXCPU);
@@ -543,12 +543,19 @@ cpu_mp_setmaxid(void)
 		mp_ncpus = cores;
 		mp_maxid = cores - 1;
 		cpu_enum_method = CPUS_FDT;
-		return;
-	}
+	} else
 #endif
+	{
+		if (bootverbose)
+			printf("No CPU data, limiting to 1 core\n");
+		mp_ncpus = 1;
+		mp_maxid = 0;
+	}
 
-	if (bootverbose)
-		printf("No CPU data, limiting to 1 core\n");
-	mp_ncpus = 1;
-	mp_maxid = 0;
+	if (TUNABLE_INT_FETCH("hw.ncpu", &cores)) {
+		if (cores > 0 && cores < mp_ncpus) {
+			mp_ncpus = cores;
+			mp_maxid = cores - 1;
+		}
+	}
 }