操作系统清华大学参考3systemtap audio

1、1OutlineOutlineBackgroundgprofDTraceSystemTapftraceS2E2Problem of Kernel InstrumentationProblem of Kernel InstrumentationKernel has a wealth of knowledge about systemKnowledge is stuck in kernel space, inaccessibleNormal means to access kernel internals:Start with kernel sourceAdd data structures an

2、d hooks where you need themCollate desired dataCreate a means to export data to userspaceRecompileRebootTestRepeatCumbersome, slow turnaround3SystemTapSystemTapCan examine or modify any parameters and local variables visible at the probe pointStatistics gathering capabilities built inA number of saf

3、ety features make it far harder to crash a running kernelAutomatically communicates with a user-level processPrevious example can be expressed far easier:global countglobal countprobe kernel.function(generic_make_request) count+; probe kernel.function(generic_make_request) count+; probe begin log(st

4、arting probe) probe begin log(starting probe) probe end printf(generic_make_request() called %d times.,count); probe end printf(generic_make_request() called %d times.,count); 4SystemTap processSystemTap process5Systemtap processing stepsSystemtap processing steps6How it worksHow it works1.SystemTap

5、 parses your code and identifies probe points and identifiers using the kernel debug info2.The script is translated into C code3.The C code is compiled into a KProbe module4.A root-privileged deamon called “stpd” is started5.The compiled kernel module is inserted6.The module exports output via the “

6、relayfs” virtual file system to stpd7.The stpd service delivers this data to the user process to output7Where to probeWhere to probeSystemtap supports a number of built-in events.8What to do with it?What to do with it?Use SystemTap-derived data to make real-time decisions about CPU scalingTwo approa

7、chs:StatisticalGiven a set of kernel metrics x1.xn, find a function f(x1.xn) that yields the ideal CPU frequencyAlgorithmicGiven a performance metric p(x1.xn), adjust the CPU frequency tentatively while observing feedback from p.CPU Scaling Agent(User process)SystemTap front-end(User process)SystemTap probe(Kernel module)CPUFreq.9ReferenceReferenceApplying the SystemTap Kernel Instrumentation Tool to CPU Freq