[PATCH v4 13/13] selftests: KVM: Add counter emulation benchmark
Oliver Upton
oupton at google.com
Thu Jul 29 09:57:51 PDT 2021
On Thu, Jul 29, 2021 at 9:56 AM Andrew Jones <drjones at redhat.com> wrote:
>
> On Thu, Jul 29, 2021 at 12:10:12AM +0000, Oliver Upton wrote:
> > 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 <ricarkol at google.com>
> > Signed-off-by: Oliver Upton <oupton at google.com>
> > ---
> > 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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