github.com/metacubex/gvisor@v0.0.0-20240320004321-933faba989ec/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  //go:build arm64
    16  // +build arm64
    17  
    18  package time
    19  
    20  // getCNTFRQ get ARM counter-timer frequency
    21  func getCNTFRQ() TSCValue
    22  
    23  // getDefaultArchOverheadCycles get default OverheadCycles based on
    24  // ARM counter-timer frequency. Usually ARM counter-timer frequency
    25  // is range from 1-50Mhz which is much less than that on x86, so we
    26  // calibrate defaultOverheadCycles for ARM.
    27  func getDefaultArchOverheadCycles() TSCValue {
    28  	// estimated the clock frequency on x86 is 1Ghz.
    29  	// 1Ghz divided by counter-timer frequency of ARM to get
    30  	// frqRatio. defaultOverheadCycles of ARM equals to that on
    31  	// x86 divided by frqRatio
    32  	cntfrq := getCNTFRQ()
    33  	frqRatio := 1000000000 / float64(cntfrq)
    34  	overheadCycles := (1 * 1000) / frqRatio
    35  	return TSCValue(overheadCycles)
    36  }
    37  
    38  // defaultOverheadTSC is the default estimated syscall overhead in TSC cycles.
    39  // It is further refined as syscalls are made.
    40  var defaultOverheadCycles = getDefaultArchOverheadCycles()
    41  
    42  // maxOverheadCycles is the maximum allowed syscall overhead in TSC cycles.
    43  var maxOverheadCycles = 100 * defaultOverheadCycles