[PATCH 1/1] selftests: KVM: set affinity of VM to right CPUs

From: Dongli Zhang
Date: Fri Sep 24 2021 - 19:34:27 EST


The nr_cpus = CPU_COUNT(&possible_mask) is the number of available CPUs in
possible_mask. As a result, the "cpu = i % nr_cpus" may always return CPU
that is not available in possible_mask.

Suppose the server has 8 CPUs. The below Failure is encountered immediately
if the task is bound to CPU 5 and 6.

==== Test Assertion Failure ====
rseq_test.c:228: i > (NR_TASK_MIGRATIONS / 2)
pid=10127 tid=10127 errno=4 - Interrupted system call
1 0x00000000004018e5: main at rseq_test.c:227
2 0x00007fcc8fc66bf6: ?? ??:0
3 0x0000000000401959: _start at ??:?
Only performed 4 KVM_RUNs, task stalled too much?

Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
---
tools/testing/selftests/kvm/rseq_test.c | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/kvm/rseq_test.c b/tools/testing/selftests/kvm/rseq_test.c
index c5e0dd664a7b..41df5173970c 100644
--- a/tools/testing/selftests/kvm/rseq_test.c
+++ b/tools/testing/selftests/kvm/rseq_test.c
@@ -10,6 +10,7 @@
#include <signal.h>
#include <syscall.h>
#include <sys/ioctl.h>
+#include <sys/sysinfo.h>
#include <asm/barrier.h>
#include <linux/atomic.h>
#include <linux/rseq.h>
@@ -43,6 +44,18 @@ static bool done;

static atomic_t seq_cnt;

+static int get_max_cpu_idx(void)
+{
+ int nproc = get_nprocs_conf();
+ int i, max = -ENOENT;
+
+ for (i = 0; i < nproc; i++)
+ if (CPU_ISSET(i, &possible_mask))
+ max = i;
+
+ return max;
+}
+
static void guest_code(void)
{
for (;;)
@@ -61,10 +74,13 @@ static void *migration_worker(void *ign)
{
cpu_set_t allowed_mask;
int r, i, nr_cpus, cpu;
+ int max_cpu_idx;

CPU_ZERO(&allowed_mask);

- nr_cpus = CPU_COUNT(&possible_mask);
+ max_cpu_idx = get_max_cpu_idx();
+ TEST_ASSERT(max_cpu_idx >= 0, "Invalid possible_mask");
+ nr_cpus = max_cpu_idx + 1;

for (i = 0; i < NR_TASK_MIGRATIONS; i++) {
cpu = i % nr_cpus;
--
2.17.1