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