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KVM: selftests: Add option to rseq test to override /dev/cpu_dma_latency

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Add a "-l <latency>" param to the rseq test so that the user can override
/dev/cpu_dma_latency, as described by the test's suggested workaround for
not being able to complete enough migrations.

cpu_dma_latency is not a normal file, even as far as procfs files go.
Writes to cpu_dma_latency only persist so long as the file is open, e.g.
so that the kernel automatically reverts back to a power-optimized state
once the sensitive workload completes.  Provide the necessary functionality
instead of effectively forcing the user to write a non-obvious wrapper.

Cc: Dongsheng Zhang <dongsheng.x.zhang@intel.com>
Cc: Zide Chen <zide.chen@intel.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20250401142238.819487-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson
2025-04-01 07:22:38 -07:00
committed by Paolo Bonzini
parent ef01cac401
commit 0297cdc12a
1 changed files with 25 additions and 6 deletions
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31
tools/testing/selftests/kvm/rseq_test.c
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@@ -196,25 +196,27 @@ static void calc_min_max_cpu(void)
static void help(const char *name)
{
puts("");
printf("usage: %s [-h] [-u]\n", name);
printf("usage: %s [-h] [-u] [-l latency]\n", name);
printf(" -u: Don't sanity check the number of successful KVM_RUNs\n");
printf(" -l: Set /dev/cpu_dma_latency to suppress deep sleep states\n");
puts("");
exit(0);
}
int main(int argc, char *argv[])
{
int r, i, snapshot, opt, fd = -1, latency = -1;
bool skip_sanity_check = false;
int r, i, snapshot;
struct kvm_vm *vm;
struct kvm_vcpu *vcpu;
u32 cpu, rseq_cpu;
int opt;
while ((opt = getopt(argc, argv, "hu")) != -1) {
while ((opt = getopt(argc, argv, "hl:u")) != -1) {
switch (opt) {
case 'u':
skip_sanity_check = true;
case 'l':
latency = atoi_paranoid(optarg);
break;
case 'h':
default:
@@ -243,6 +245,20 @@ int main(int argc, char *argv[])
pthread_create(&migration_thread, NULL, migration_worker,
(void *)(unsigned long)syscall(SYS_gettid));
if (latency >= 0) {
/*
* Writes to cpu_dma_latency persist only while the file is
* open, i.e. it allows userspace to provide guaranteed latency
* while running a workload. Keep the file open until the test
* completes, otherwise writing cpu_dma_latency is meaningless.
*/
fd = open("/dev/cpu_dma_latency", O_RDWR);
TEST_ASSERT(fd >= 0, __KVM_SYSCALL_ERROR("open() /dev/cpu_dma_latency", fd));
r = write(fd, &latency, 4);
TEST_ASSERT(r >= 1, "Error setting /dev/cpu_dma_latency");
}
for (i = 0; !done; i++) {
vcpu_run(vcpu);
TEST_ASSERT(get_ucall(vcpu, NULL) == UCALL_SYNC,
@@ -278,6 +294,9 @@ int main(int argc, char *argv[])
"rseq CPU = %d, sched CPU = %d", rseq_cpu, cpu);
}
if (fd > 0)
close(fd);
/*
* Sanity check that the test was able to enter the guest a reasonable
* number of times, e.g. didn't get stalled too often/long waiting for
@@ -293,8 +312,8 @@ int main(int argc, char *argv[])
TEST_ASSERT(skip_sanity_check || i > (NR_TASK_MIGRATIONS / 2),
"Only performed %d KVM_RUNs, task stalled too much?\n\n"
" Try disabling deep sleep states to reduce CPU wakeup latency,\n"
" e.g. via cpuidle.off=1 or setting /dev/cpu_dma_latency to '0',\n"
" or run with -u to disable this sanity check.", i);
" e.g. via cpuidle.off=1 or via -l <latency>, or run with -u to\n"
" disable this sanity check.", i);
pthread_join(migration_thread, NULL);