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 
20 using namespace lldb_private;
21 using namespace process_linux;
22 using namespace llvm;
23 
24 /// Helper function to read current TSC value.
25 ///
26 /// This code is based on llvm/xray.
27 static 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(inconvertibleErrorCode(),
39                              "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.
51 TEST(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(params.takeError());
68 
69   Expected<uint64_t> tsc_before_sleep = readTsc();
70   sleep(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(tsc_before_sleep.takeError());
76   if (!tsc_after_sleep)
77     GTEST_SKIP() << toString(tsc_after_sleep.takeError());
78 
79   uint64_t converted_tsc_diff =
80       params->ToNanos(*tsc_after_sleep) - params->ToNanos(*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