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