src/cpu/kvm/timer.cc

   1 /*
   2  * Copyright (c) 2012 ARM Limited
   3  * All rights reserved
   4  *
   5  * The license below extends only to copyright in the software and shall
   6  * not be construed as granting a license to any other intellectual
   7  * property including but not limited to intellectual property relating
   8  * to a hardware implementation of the functionality of the software
   9  * licensed hereunder.  You may use the software subject to the license
  10  * terms below provided that you ensure that this notice is replicated
  11  * unmodified and in its entirety in all distributions of the software,
  12  * modified or unmodified, in source code or in binary form.
  13  *
  14  * Redistribution and use in source and binary forms, with or without
  15  * modification, are permitted provided that the following conditions are
  16  * met: redistributions of source code must retain the above copyright
  17  * notice, this list of conditions and the following disclaimer;
  18  * redistributions in binary form must reproduce the above copyright
  19  * notice, this list of conditions and the following disclaimer in the
  20  * documentation and/or other materials provided with the distribution;
  21  * neither the name of the copyright holders nor the names of its
  22  * contributors may be used to endorse or promote products derived from
  23  * this software without specific prior written permission.
  24  *
  25  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  26  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  27  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  28  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  29  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  30  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  31  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  32  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  33  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  34  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  35  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  36  *
  37  * Authors: Andreas Sandberg
  38  */
  39
  40 #include <algorithm>
  41 #include <csignal>
  42 #include <ctime>
  43 #include <unistd.h>
  44 #include <sys/syscall.h>
  45
  46 #include "base/misc.hh"
  47 #include "base/trace.hh"
  48 #include "cpu/kvm/timer.hh"
  49 #include "debug/KvmTimer.hh"
  50
  51 /* According to timer_create(2), the value SIGEV_THREAD_ID can be used
  52  * to specify which thread a timer signal gets delivered to. According
  53  * to the man page, the member sigev_notify_thread is used to specify
  54  * the TID. This member is currently not defined by default in
  55  * siginfo.h on x86, so we define it here as a workaround.
  56  */
  57 #ifndef sigev_notify_thread_id
  58 #define sigev_notify_thread_id     _sigev_un._tid
  59 #endif
  60
  61 static pid_t
  62 gettid()
  63 {
  64     return syscall(__NR_gettid);
  65 }
  66
  67 /**
  68  * Minimum number of cycles that a host can spend in a KVM call (used
  69  * to calculate the resolution of some timers).
  70  *
  71  * The value of this constant is a bit arbitrary, but in practice, we
  72  * can't really do anything useful in less than ~1000 cycles.
  73  */
  74 static const uint64_t MIN_HOST_CYCLES = 1000;
  75
  76 PosixKvmTimer::PosixKvmTimer(int signo, clockid_t clockID,
  77                              float hostFactor, Tick hostFreq)
  78     : BaseKvmTimer(signo, hostFactor, hostFreq),
  79       clockID(clockID)
  80 {
  81     struct sigevent sev;
  82
  83     sev.sigev_notify = SIGEV_THREAD_ID;
  84     sev.sigev_signo = signo;
  85     sev.sigev_notify_thread_id = gettid();
  86     sev.sigev_value.sival_ptr = NULL;
  87
  88     while (timer_create(clockID, &sev, &timer) == -1) {
  89         if (errno != EAGAIN)
  90             panic("timer_create: %i", errno);
  91     }
  92 }
  93
  94 PosixKvmTimer::~PosixKvmTimer()
  95 {
  96     timer_delete(timer);
  97 }
  98
  99 void
 100 PosixKvmTimer::arm(Tick ticks)
 101 {
 102     struct itimerspec ts;
 103     memset(&ts, 0, sizeof(ts));
 104
 105     ts.it_interval.tv_sec = 0;
 106     ts.it_interval.tv_nsec = 0;
 107     ts.it_value.tv_sec = hostNs(ticks) / 1000000000ULL;
 108     ts.it_value.tv_nsec = hostNs(ticks) % 1000000000ULL;
 109
 110     assert(ts.it_value.tv_nsec > 0 || ts.it_value.tv_sec > 0);
 111
 112     DPRINTF(KvmTimer, "Arming POSIX timer: %i ticks (%is%ins)\n",
 113             ticks, ts.it_value.tv_sec, ts.it_value.tv_nsec);
 114
 115     if (timer_settime(timer, 0, &ts, NULL) == -1)
 116         panic("PosixKvmTimer: Failed to arm timer\n");
 117 }
 118
 119 void
 120 PosixKvmTimer::disarm()
 121 {
 122     struct itimerspec ts;
 123     memset(&ts, 0, sizeof(ts));
 124
 125     DPRINTF(KvmTimer, "Disarming POSIX timer\n");
 126
 127     if (timer_settime(timer, 0, &ts, NULL) == -1)
 128         panic("PosixKvmTimer: Failed to disarm timer\n");
 129 }
 130
 131 Tick
 132 PosixKvmTimer::calcResolution()
 133 {
 134     struct timespec ts;
 135
 136     if (clock_getres(clockID, &ts) == -1)
 137         panic("PosixKvmTimer: Failed to get timer resolution\n");
 138
 139     const uint64_t res_ns(ts.tv_sec * 1000000000ULL + ts.tv_nsec);
 140     // We preferrably want ticksFromHostNs() to calculate the the
 141     // ceiling rather than truncating the value. However, there are
 142     // other cases where truncating is fine, so we just add 1 here to
 143     // make sure that the actual resolution is strictly less than what
 144     // we return. We could get all kinds of nasty behavior if
 145     // arm(resolution) is called and the resulting time is 0 (which
 146     // could happen if we truncate the results and the resolution is
 147     // 1ns).
 148     const Tick resolution(ticksFromHostNs(res_ns) + 1);
 149     // It might not make sense to enter into KVM for less than a
 150     // certain number of host cycles. In some systems (e.g., Linux)
 151     // the resolution of the timer we use is 1ns (a few cycles on most
 152     // CPUs), which isn't very useful.
 153     const Tick min_cycles(ticksFromHostCycles(MIN_HOST_CYCLES));
 154
 155     return std::max(resolution, min_cycles);
 156 }
 157
 158
 159 PerfKvmTimer::PerfKvmTimer(PerfKvmCounter &ctr,
 160                            int signo, float hostFactor, Tick hostFreq)
 161     : BaseKvmTimer(signo, hostFactor, hostFreq),
 162       hwOverflow(ctr)
 163 {
 164     hwOverflow.enableSignals(signo);
 165 }
 166
 167 PerfKvmTimer::~PerfKvmTimer()
 168 {
 169 }
 170
 171 void
 172 PerfKvmTimer::arm(Tick ticks)
 173 {
 174     hwOverflow.period(hostCycles(ticks));
 175     hwOverflow.refresh(1);
 176 }
 177
 178 void
 179 PerfKvmTimer::disarm()
 180 {
 181     hwOverflow.stop();
 182 }
 183
 184 Tick
 185 PerfKvmTimer::calcResolution()
 186 {
 187     return ticksFromHostCycles(MIN_HOST_CYCLES);
 188 }