On Thu, Jul 29, 2021 at 9:56 AM Andrew Jones [off-list ref] wrote:

On Thu, Jul 29, 2021 at 12:10:12AM +0000, Oliver Upton wrote:

quoted

Add a test case for counter emulation on arm64. A side effect of how KVM
handles physical counter offsetting on non-ECV systems is that the
virtual counter will always hit hardware and the physical could be
emulated. Force emulation by writing a nonzero offset to the physical
counter and compare the elapsed cycles to a direct read of the hardware
register.

Reviewed-by: Ricardo Koller <redacted>
Signed-off-by: Oliver Upton <redacted>
---
 tools/testing/selftests/kvm/.gitignore        |   1 +
 tools/testing/selftests/kvm/Makefile          |   1 +
 .../kvm/aarch64/counter_emulation_benchmark.c | 215 ++++++++++++++++++
 3 files changed, 217 insertions(+)
 create mode 100644 tools/testing/selftests/kvm/aarch64/counter_emulation_benchmark.c

diff --git a/tools/testing/selftests/kvm/.gitignore b/tools/testing/selftests/kvm/.gitignore
index 3d2585f0bffc..a23198ea6e7a 100644
--- a/tools/testing/selftests/kvm/.gitignore
+++ b/tools/testing/selftests/kvm/.gitignore

@@ -1,5 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0-only
 /aarch64/debug-exceptions
+/aarch64/counter_emulation_benchmark
 /aarch64/get-reg-list
 /aarch64/vgic_init
 /s390x/memop

diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
index fab42e7c23ee..db8706eb6104 100644
--- a/tools/testing/selftests/kvm/Makefile
+++ b/tools/testing/selftests/kvm/Makefile

@@ -88,6 +88,7 @@ TEST_GEN_PROGS_x86_64 += kvm_binary_stats_test
 TEST_GEN_PROGS_x86_64 += system_counter_offset_test

 TEST_GEN_PROGS_aarch64 += aarch64/debug-exceptions
+TEST_GEN_PROGS_aarch64 += aarch64/counter_emulation_benchmark
 TEST_GEN_PROGS_aarch64 += aarch64/get-reg-list
 TEST_GEN_PROGS_aarch64 += aarch64/vgic_init
 TEST_GEN_PROGS_aarch64 += demand_paging_test

diff --git a/tools/testing/selftests/kvm/aarch64/counter_emulation_benchmark.c b/tools/testing/selftests/kvm/aarch64/counter_emulation_benchmark.c
new file mode 100644
index 000000000000..73aeb6cdebfe
--- /dev/null
+++ b/tools/testing/selftests/kvm/aarch64/counter_emulation_benchmark.c

@@ -0,0 +1,215 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * counter_emulation_benchmark.c -- test to measure the effects of counter
+ * emulation on guest reads of the physical counter.
+ *
+ * Copyright (c) 2021, Google LLC.
+ */
+
+#define _GNU_SOURCE
+#include <asm/kvm.h>
+#include <linux/kvm.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include "kvm_util.h"
+#include "processor.h"
+#include "test_util.h"
+
+#define VCPU_ID 0
+
+static struct counter_values {
+     uint64_t cntvct_start;
+     uint64_t cntpct;
+     uint64_t cntvct_end;
+} counter_values;
+
+static uint64_t nr_iterations = 1000;
+
+static void do_test(void)
+{
+     /*
+      * Open-coded approach instead of using helper methods to keep a tight
+      * interval around the physical counter read.
+      */
+     asm volatile("isb\n\t"
+                  "mrs %[cntvct_start], cntvct_el0\n\t"
+                  "isb\n\t"
+                  "mrs %[cntpct], cntpct_el0\n\t"
+                  "isb\n\t"
+                  "mrs %[cntvct_end], cntvct_el0\n\t"
+                  "isb\n\t"
+                  : [cntvct_start] "=r"(counter_values.cntvct_start),
+                  [cntpct] "=r"(counter_values.cntpct),
+                  [cntvct_end] "=r"(counter_values.cntvct_end));
+}
+
+static void guest_main(void)
+{
+     int i;
+
+     for (i = 0; i < nr_iterations; i++) {
+             do_test();
+             GUEST_SYNC(i);
+     }
+
+     for (i = 0; i < nr_iterations; i++) {
+             do_test();
+             GUEST_SYNC(i);
+     }
+
+     GUEST_DONE();
+}
+
+static bool enter_guest(struct kvm_vm *vm)
+{
+     struct ucall uc;
+
+     vcpu_ioctl(vm, VCPU_ID, KVM_RUN, NULL);
+
+     switch (get_ucall(vm, VCPU_ID, &uc)) {
+     case UCALL_DONE:
+             return true;
+     case UCALL_SYNC:
+             break;
+     case UCALL_ABORT:
+             TEST_ASSERT(false, "%s at %s:%ld", (const char *)uc.args[0],
+                         __FILE__, uc.args[1]);
+             break;
+     default:
+             TEST_ASSERT(false, "unexpected exit: %s",
+                         exit_reason_str(vcpu_state(vm, VCPU_ID)->exit_reason));
+             break;
+     }
+
+     /* more work to do in the guest */
+     return false;
+}
+
+static double counter_frequency(void)
+{
+     uint32_t freq;
+
+     asm volatile("mrs %0, cntfrq_el0"
+                  : "=r" (freq));
+
+     return freq / 1000000.0;
+}
+
+static void log_csv(FILE *csv, bool trapped)
+{
+     double freq = counter_frequency();
+
+     fprintf(csv, "%s,%.02f,%lu,%lu,%lu\n",
+             trapped ? "true" : "false", freq,
+             counter_values.cntvct_start,
+             counter_values.cntpct,
+             counter_values.cntvct_end);
+}
+
+static double run_loop(struct kvm_vm *vm, FILE *csv, bool trapped)
+{
+     double avg = 0;
+     int i;
+
+     for (i = 0; i < nr_iterations; i++) {
+             uint64_t delta;
+
+             TEST_ASSERT(!enter_guest(vm), "guest exited unexpectedly");
+             sync_global_from_guest(vm, counter_values);
+
+             if (csv)
+                     log_csv(csv, trapped);
+
+             delta = counter_values.cntvct_end - counter_values.cntvct_start;
+             avg = ((avg * i) + delta) / (i + 1);
+     }
+
+     return avg;
+}
+
+static void setup_counter(struct kvm_vm *vm, uint64_t offset)
+{
+     vcpu_access_device_attr(vm, VCPU_ID, KVM_ARM_VCPU_TIMER_CTRL,
+                             KVM_ARM_VCPU_TIMER_OFFSET_PTIMER, &offset,
+                             true);
+}
+
+static void run_tests(struct kvm_vm *vm, FILE *csv)
+{
+     double avg_trapped, avg_native, freq;
+
+     freq = counter_frequency();
+
+     if (csv)
+             fputs("trapped,freq_mhz,cntvct_start,cntpct,cntvct_end\n", csv);
+
+     /* no physical offsetting; kvm allows reads of cntpct_el0 */
+     setup_counter(vm, 0);
+     avg_native = run_loop(vm, csv, false);
+
+     /* force emulation of the physical counter */
+     setup_counter(vm, 1);
+     avg_trapped = run_loop(vm, csv, true);
+
+     TEST_ASSERT(enter_guest(vm), "guest didn't run to completion");
+     pr_info("%lu iterations: average cycles (@%.02fMHz) native: %.02f, trapped: %.02f\n",
+             nr_iterations, freq, avg_native, avg_trapped);
+}
+
+static void usage(const char *program_name)
+{
+     fprintf(stderr,
+             "Usage: %s [-h] [-o csv_file] [-n iterations]\n"
+             "  -h prints this message\n"
+             "  -n number of test iterations (default: %lu)\n"
+             "  -o csv file to write data\n",
+             program_name, nr_iterations);
+}
+
+int main(int argc, char **argv)
+{
+     struct kvm_vm *vm;
+     FILE *csv = NULL;
+     int opt;
+
+     while ((opt = getopt(argc, argv, "hn:o:")) != -1) {
+             switch (opt) {
+             case 'o':
+                     csv = fopen(optarg, "w");
+                     if (!csv) {
+                             fprintf(stderr, "failed to open file '%s': %d\n",
+                                     optarg, errno);
+                             exit(1);
+                     }
+                     break;
+             case 'n':
+                     nr_iterations = strtoul(optarg, NULL, 0);
+                     break;
+             default:
+                     fprintf(stderr, "unrecognized option: '-%c'\n", opt);
+                     /* fallthrough */
+             case 'h':
+                     usage(argv[0]);
+                     exit(1);
+             }
+     }
+
+     vm = vm_create_default(VCPU_ID, 0, guest_main);
+     sync_global_to_guest(vm, nr_iterations);
+     ucall_init(vm, NULL);
+
+     if (_vcpu_has_device_attr(vm, VCPU_ID, KVM_ARM_VCPU_TIMER_CTRL,
+                               KVM_ARM_VCPU_TIMER_OFFSET_PTIMER)) {
+             print_skip("KVM_ARM_VCPU_TIMER_OFFSET_PTIMER not supported.");
+             exit(KSFT_SKIP);
+     }
+
+     run_tests(vm, csv);
+     kvm_vm_free(vm);
+
+     if (csv)
+             fclose(csv);
+}
--

2.32.0.432.gabb21c7263-goog

I skimmed through this, but didn't see any changes from v3 where I had a
couple comments.

Ah, yes, I missed those comments by accident. Thanks!

--
Oliver

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