github.com/SagerNet/gvisor@v0.0.0-20210707092255-7731c139d75c/pkg/sentry/time/sampler_arm64.go (about)

     1  // Copyright 2018 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  //+build arm64
    16  
    17  package time
    18  
    19  // getCNTFRQ get ARM counter-timer frequency
    20  func getCNTFRQ() TSCValue
    21  
    22  // getDefaultArchOverheadCycles get default OverheadCycles based on
    23  // ARM counter-timer frequency. Usually ARM counter-timer frequency
    24  // is range from 1-50Mhz which is much less than that on x86, so we
    25  // calibrate defaultOverheadCycles for ARM.
    26  func getDefaultArchOverheadCycles() TSCValue {
    27  	// estimated the clock frequency on x86 is 1Ghz.
    28  	// 1Ghz devided by counter-timer frequency of ARM to get
    29  	// frqRatio. defaultOverheadCycles of ARM equals to that on
    30  	// x86 devided by frqRatio
    31  	cntfrq := getCNTFRQ()
    32  	frqRatio := 1000000000 / cntfrq
    33  	overheadCycles := (1 * 1000) / frqRatio
    34  	return overheadCycles
    35  }
    36  
    37  // defaultOverheadTSC is the default estimated syscall overhead in TSC cycles.
    38  // It is further refined as syscalls are made.
    39  var defaultOverheadCycles = getDefaultArchOverheadCycles()
    40  
    41  // maxOverheadCycles is the maximum allowed syscall overhead in TSC cycles.
    42  var maxOverheadCycles = 100 * defaultOverheadCycles