diff options
Diffstat (limited to 'src/common/Cycles.cc')
| -rw-r--r-- | src/common/Cycles.cc | 220 |
1 files changed, 220 insertions, 0 deletions
diff --git a/src/common/Cycles.cc b/src/common/Cycles.cc new file mode 100644 index 000000000..2ebd24699 --- /dev/null +++ b/src/common/Cycles.cc @@ -0,0 +1,220 @@ +// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*- +// vim: ts=8 sw=2 smarttab +/* + * Ceph - scalable distributed file system + * + * Copyright (C) 2014 UnitedStack <haomai@unitedstack.com> + * + * Author: Haomai Wang <haomaiwang@gmail.com> + * + * This is free software; you can redistribute it and/or + * modify it under the terms of the GNU Lesser General Public + * License version 2.1, as published by the Free Software + * Foundation. See file COPYING. + * + */ +/* Copyright (c) 2011-2014 Stanford University + * + * Permission to use, copy, modify, and distribute this software for any + * purpose with or without fee is hereby granted, provided that the above + * copyright notice and this permission notice appear in all copies. + * + * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR(S) DISCLAIM ALL WARRANTIES + * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF + * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL AUTHORS BE LIABLE FOR + * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES + * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN + * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF + * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. + */ + +#include "debug.h" +#include "Cycles.h" + +double Cycles::cycles_per_sec = 0; + +/** + * Perform once-only overall initialization for the Cycles class, such + * as calibrating the clock frequency. This method must be called + * before using the Cycles module. + * + * It is not initialized by default because the timing loops cause + * general process startup times to balloon + * (http://tracker.ceph.com/issues/15225). + */ +void Cycles::init() +{ + if (cycles_per_sec != 0) + return; + + // Skip initialization if rtdsc is not implemented + if (rdtsc() == 0) + return; + + // Compute the frequency of the fine-grained CPU timer: to do this, + // take parallel time readings using both rdtsc and gettimeofday. + // After 10ms have elapsed, take the ratio between these readings. + + struct timeval start_time, stop_time; + uint64_t micros; + double old_cycles; + + // There is one tricky aspect, which is that we could get interrupted + // between calling gettimeofday and reading the cycle counter, in which + // case we won't have corresponding readings. To handle this (unlikely) + // case, compute the overall result repeatedly, and wait until we get + // two successive calculations that are within 0.1% of each other. + old_cycles = 0; + while (1) { + if (gettimeofday(&start_time, NULL) != 0) { + ceph_abort_msg("couldn't read clock"); + } + uint64_t start_cycles = rdtsc(); + while (1) { + if (gettimeofday(&stop_time, NULL) != 0) { + ceph_abort_msg("couldn't read clock"); + } + uint64_t stop_cycles = rdtsc(); + micros = (stop_time.tv_usec - start_time.tv_usec) + + (stop_time.tv_sec - start_time.tv_sec)*1000000; + if (micros > 10000) { + cycles_per_sec = static_cast<double>(stop_cycles - start_cycles); + cycles_per_sec = 1000000.0*cycles_per_sec/ static_cast<double>(micros); + break; + } + } + double delta = cycles_per_sec/1000.0; + if ((old_cycles > (cycles_per_sec - delta)) && + (old_cycles < (cycles_per_sec + delta))) { + return; + } + old_cycles = cycles_per_sec; + } +} + +/** + * Return the number of CPU cycles per second. + */ +double Cycles::per_second() +{ + return get_cycles_per_sec(); +} + +/** + * Given an elapsed time measured in cycles, return a floating-point number + * giving the corresponding time in seconds. + * \param cycles + * Difference between the results of two calls to rdtsc. + * \param cycles_per_sec + * Optional parameter to specify the frequency of the counter that #cycles + * was taken from. Useful when converting a remote machine's tick counter + * to seconds. The default value of 0 will use the local processor's + * computed counter frequency. + * \return + * The time in seconds corresponding to cycles. + */ +double Cycles::to_seconds(uint64_t cycles, double cycles_per_sec) +{ + if (cycles_per_sec == 0) + cycles_per_sec = get_cycles_per_sec(); + return static_cast<double>(cycles)/cycles_per_sec; +} + +/** + * Given a time in seconds, return the number of cycles that it + * corresponds to. + * \param seconds + * Time in seconds. + * \param cycles_per_sec + * Optional parameter to specify the frequency of the counter that #cycles + * was taken from. Useful when converting a remote machine's tick counter + * to seconds. The default value of 0 will use the local processor's + * computed counter frequency. + * \return + * The approximate number of cycles corresponding to #seconds. + */ +uint64_t Cycles::from_seconds(double seconds, double cycles_per_sec) +{ + if (cycles_per_sec == 0) + cycles_per_sec = get_cycles_per_sec(); + return (uint64_t) (seconds*cycles_per_sec + 0.5); +} + +/** + * Given an elapsed time measured in cycles, return an integer + * giving the corresponding time in microseconds. Note: to_seconds() + * is faster than this method. + * \param cycles + * Difference between the results of two calls to rdtsc. + * \param cycles_per_sec + * Optional parameter to specify the frequency of the counter that #cycles + * was taken from. Useful when converting a remote machine's tick counter + * to seconds. The default value of 0 will use the local processor's + * computed counter frequency. + * \return + * The time in microseconds corresponding to cycles (rounded). + */ +uint64_t Cycles::to_microseconds(uint64_t cycles, double cycles_per_sec) +{ + return to_nanoseconds(cycles, cycles_per_sec) / 1000; +} + +/** + * Given an elapsed time measured in cycles, return an integer + * giving the corresponding time in nanoseconds. Note: to_seconds() + * is faster than this method. + * \param cycles + * Difference between the results of two calls to rdtsc. + * \param cycles_per_sec + * Optional parameter to specify the frequency of the counter that #cycles + * was taken from. Useful when converting a remote machine's tick counter + * to seconds. The default value of 0 will use the local processor's + * computed counter frequency. + * \return + * The time in nanoseconds corresponding to cycles (rounded). + */ +uint64_t Cycles::to_nanoseconds(uint64_t cycles, double cycles_per_sec) +{ + if (cycles_per_sec == 0) + cycles_per_sec = get_cycles_per_sec(); + return (uint64_t) (1e09*static_cast<double>(cycles)/cycles_per_sec + 0.5); +} + +/** + * Given a number of nanoseconds, return an approximate number of + * cycles for an equivalent time length. + * \param ns + * Number of nanoseconds. + * \param cycles_per_sec + * Optional parameter to specify the frequency of the counter that #cycles + * was taken from. Useful when converting a remote machine's tick counter + * to seconds. The default value of 0 will use the local processor's + * computed counter frequency. + * \return + * The approximate number of cycles for the same time length. + */ +uint64_t +Cycles::from_nanoseconds(uint64_t ns, double cycles_per_sec) +{ + if (cycles_per_sec == 0) + cycles_per_sec = get_cycles_per_sec(); + return (uint64_t) (static_cast<double>(ns)*cycles_per_sec/1e09 + 0.5); +} + +/** + * Busy wait for a given number of microseconds. + * Callers should use this method in most reasonable cases as opposed to + * usleep for accurate measurements. Calling usleep may put the the processor + * in a low power mode/sleep state which reduces the clock frequency. + * So, each time the process/thread wakes up from usleep, it takes some time + * to ramp up to maximum frequency. Thus meausrements often incur higher + * latencies. + * \param us + * Number of microseconds. + */ +void +Cycles::sleep(uint64_t us) +{ + uint64_t stop = Cycles::rdtsc() + Cycles::from_nanoseconds(1000*us); + while (Cycles::rdtsc() < stop); +} |