1//===-- PerfTests.cpp -----------------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#ifdef __x86_64__
10
11#include "Perf.h"
12
13#include "llvm/Support/Error.h"
14
15#include "gtest/gtest.h"
16
17#include <chrono>
18#include <cstdint>
19
20using namespace lldb_private;
21using namespace process_linux;
22using namespace llvm;
23
24/// Helper function to read current TSC value.
25///
26/// This code is based on llvm/xray.
27static Expected<uint64_t> readTsc() {
28
29 unsigned int eax, ebx, ecx, edx;
30
31 // We check whether rdtscp support is enabled. According to the x86_64 manual,
32 // level should be set at 0x80000001, and we should have a look at bit 27 in
33 // EDX. That's 0x8000000 (or 1u << 27).
34 __asm__ __volatile__("cpuid"
35 : "=a"(eax), "=b"(ebx), "=c"(ecx), "=d"(edx)
36 : "0"(0x80000001));
37 if (!(edx & (1u << 27))) {
38 return createStringError(EC: inconvertibleErrorCode(),
39 S: "Missing rdtscp support.");
40 }
41
42 unsigned cpu;
43 unsigned long rax, rdx;
44
45 __asm__ __volatile__("rdtscp\n" : "=a"(rax), "=d"(rdx), "=c"(cpu)::);
46
47 return (rdx << 32) + rax;
48}
49
50// Test TSC to walltime conversion based on perf conversion values.
51TEST(Perf, TscConversion) {
52 // This test works by first reading the TSC value directly before
53 // and after sleeping, then converting these values to nanoseconds, and
54 // finally ensuring the difference is approximately equal to the sleep time.
55 //
56 // There will be slight overhead associated with the sleep call, so it isn't
57 // reasonable to expect the difference to be exactly equal to the sleep time.
58
59 const int SLEEP_SECS = 1;
60 std::chrono::nanoseconds SLEEP_NANOS{std::chrono::seconds(SLEEP_SECS)};
61
62 Expected<LinuxPerfZeroTscConversion> params =
63 LoadPerfTscConversionParameters();
64
65 // Skip the test if the conversion parameters aren't available.
66 if (!params)
67 GTEST_SKIP() << toString(E: params.takeError());
68
69 Expected<uint64_t> tsc_before_sleep = readTsc();
70 sleep(seconds: SLEEP_SECS);
71 Expected<uint64_t> tsc_after_sleep = readTsc();
72
73 // Skip the test if we are unable to read the TSC value.
74 if (!tsc_before_sleep)
75 GTEST_SKIP() << toString(E: tsc_before_sleep.takeError());
76 if (!tsc_after_sleep)
77 GTEST_SKIP() << toString(E: tsc_after_sleep.takeError());
78
79 uint64_t converted_tsc_diff =
80 params->ToNanos(tsc: *tsc_after_sleep) - params->ToNanos(tsc: *tsc_before_sleep);
81
82 std::chrono::microseconds acceptable_overhead(500);
83
84 ASSERT_GE(converted_tsc_diff, static_cast<uint64_t>(SLEEP_NANOS.count()));
85 ASSERT_LT(converted_tsc_diff,
86 static_cast<uint64_t>((SLEEP_NANOS + acceptable_overhead).count()));
87}
88
89#endif // __x86_64__
90

source code of lldb/unittests/Process/Linux/PerfTests.cpp