EOI_INDUCEDivybridge

ivybridge  时间:2021-03-28  阅读:()
MessagePassingWorkloadsinKVMDavidMatlack,dmatlack@google.
com1MessagePassingWorkloadsLoopbackTCP_RRIPIandHLTDISCLAIMER:x86andIntelVT-xHaltPollingInterruptsandquestionsarewelcome!
Overview2Usually,anythingthatfrequentlyswitchesbetweenrunningandidle.
Event-drivenworkloadsMemcacheLAMPserversRedisMultithreadedworkloadsusinglowlatencywait/signalprimitivesforcoordination.
WindowsEventObjectspthread_cond_wait/pthread_cond_signalInter-processcommunicationTCP_RR(benchmark)MessagePassingWorkloads3Intuition:Workloadswhichdon'tinvolveIOvirtualizationshouldrunatnearnativeperformance.
Reality:MessagePassingWorkloadsmaynotinvolveanyIObutwillstillperformnXworsethannative.
(loopback)Memcache:2xhigherlatency.
WindowsEventObjects:3-4xhigherlatency.
MessagePassingWorkloads4MessagePassingWorkloads2.
Receive1bytefromclient.
Send1byteback.
1.
Send1bytetoserver.
3.
Receive1bytefromserver.
Microbenchmark:LoopbackTCP_RRClientandServerping-pong1-byteofdataoveranestablishedTCPconnection.
Loopback:Nonetworkingdevices(realorvirtual)involved.
Performance:Latencyofeachtransaction.
Onetransaction:(idle)(idle)(idle)ClientServer5LoopbackTCP_RRPerformance6Host:IvyBridge3.
11KernelGuest:DebianWheezyBackports(3.
16Kernel)3xhigherlatency25usslowerMessagePassingon1CPUContextSwitchMessagePassingon>1CPUInterprocessor-InterruptsWhat'sgoingonunderthehoodVMEXITsareagoodplacetostartlooking.
KVMhasbuilt-inVMEXITcountersandtimers.
perf-kvm(1)VirtualOverheadsofTCP_RR7VirtualOverheadsofTCP_RRTotalNumberofVMEXITsVMEXITs/Transaction1VCPU2VCPU1VCPU2VCPUEXTERNAL_INTERRUPT16705123710.
020.
07MSR_WRITE259917043340.
009.
58IO_INSTRUCTION17867620.
000.
00EOI_INDUCED613250.
000.
00EXCEPTION_NMI289310.
000.
00CPUID2521120.
000.
00CR_ACCESS1712720.
000.
00HLT343543930.
001.
99EPT_VIOLATION200.
000.
00PAUSE_INSTRUCTION020140.
000.
012HLTperTransaction10MSR_WRITEperTransaction8HLTsofTCP_RR2HLTCPUinstruction.
StopexecutinginstructionsonthisCPUuntilaninterruptarrives.
VCPUwishestostopexecutinginstructions.
GuestOShasdecidedthatthereisnothingtodo.
Nothingtodo==idle.
Messagepassingworkloadsswitchbetweenrunningandidle.
.
.
910MSR_WRITE"WritetoModelSpecificRegister"instructionexecutedintheguest.
8APICTimer"InitialCount"Register(MSR838)Writtentostartaper-CPUtimer.
"Startcountingdownandfireaninterruptwhenyougettozero.
"ArtifactofNOHZguestkernel.
2APICInterruptCommandRegister(MSR830)Usedtosendinterprocessor-interrupts(IPI).
Usedtodeliver"messages"betweenclient/serverprocessesrunningonseparateCPUs.
MSR_WRITEsofTCP_RR10VMEXITsofTCP_RRVMEXITSAPICTimerRegisterAPICInterruptCommandRegister(IPI)HLTclientclientidleserveridleidle1.
Send1bytetoserver.
Waitforresponse.
2.
Receive1bytefromclient.
Send1byteback.
3.
Receive1bytefromserver.
VCPU0VCPU111HLTHLTHLTIPIIPIAPICTIMERAPICTIMERAPICTIMERAPICTIMERVMEXITsofTCP_RRVMEXITSAPICTimerRegisterAPICInterruptCommandRegister(IPI)HLTclientclientidleserveridleidle1.
Send1bytetoserver.
Waitforresponse.
2.
Receive1bytefromclient.
Send1byteback.
3.
Receive1bytefromserver.
VCPU0VCPU112HLTHLTHLTIPIIPIAPICTIMERAPICTIMERAPICTIMERAPICTIMERCriticalPath8pertransaction4onthecriticalpathNOHZ(ticklessguestkernel)"Disable"scheduler-tickuponenteringidle.
"Enable"scheduler-tickuponleavingidle.
scheduler-tick==APICTimer(couldalsobeTSCDeadlineTimer)Why2writespertransitioninto/outofidlehrtimer_cancelhrtimer_startAdds3-5ustoround-triplatency.
APICTimer"InitialCount"Register13HLT:x86Instruction.
CPUstopsexecutinginstructionsuntilaninterruptarrives.
ThispartofHLTisnotonthecriticalpath!
HowitworksinKVMPlaceVCPUthreadonawaitqueue.
YieldtheCPUtoanotherthread.
HLTkvm_vcpu_block->schedule()VMEXITHLTcontextswitchtoanotherusertask,kernelthread,oridleVCPU(guest)PCPU(KVM)14kvm_sched_outSendinganIPItowakeupaHLT-edCPU.
Onthecriticalpath!
IPI+HLTWRMSR:APICInterruptCommandRegisterkvm_vcpu_kickreturnfromschedule()inkvm_vcpu_block()vmx_vcpu_runIPIISRVMEXITVMRESUMEVCPU1VCPU0(HLT-ed)guesthostkvm_sched_in*VMEXITandVMRESUMEimplementedinHardware.
time15SendinganIPItowakeupaHLT-edCPU.
Onthecriticalpath!
Sameoperationonbaremetalisentirelyimplementedinhardware.
HowmuchoverheadfromvirtualizationUnlikeAPIC_TMICT,can'tjusttimeVMEXITs.
Wecancomparewiththesameoperationonphysicalhardware.
IPI+HLT16KVMversusHardwareRing0Microbenchmark(kvm-unit-tests)1.
VCPU0:HLT.
2.
~100usdelay3.
VCPU1:A=RDTSC4.
VCPU1:SendIPIto[V]CPU0.
5.
VCPU0:B=RDTSC(firstinstructionofIPIISR).
6.
Latency=B-A7.
Repeat.
RuninKVMguestandonbare-metal.
Compare!
17VMRESUMEWRMSRkvm_vcpu_kickreturnfromschedule()inkvm_vcpu_block()vmx_vcpu_runIPIISRVMEXITVCPU1VCPU0(HLT-ed)guesthostkvm_sched_intimeKVMversusHardwareA=RDTSCB=RDTSC18Median:KVMis12xslowerPathologicalcase(witnessed):KVMis400xslowerBestcase(witnessed):KVMis11xslowerKVM:5.
7us;Hardware:0.
5usKVMversusHardwareCyclesKVMHardwareMin137001200Average15800120050%ile14900120090%ile16000130099%ile249001300Max5210001400Host:SandyBridge@2.
6GHz3.
11KernelKVMperformanceissimilaronIvyBridge(5.
6us)andHaswell(4.
9us).
19Notesaboutthisbenchmark:NoguestFPUtosave/restore.
Hostotherwiseidle(VCPUcontextswitchestoidleonHLT).
Hostpowermanagementnottheculprit.
KVMversusHardware20KVMHLTInternalsSoKVMisslowatdeliveringIPIsand/orcomingoutofHLT.
ButwhyPossibleculprits:WRMSRvmx_vcpu_runIPIISRVMEXITVMRESUMEVCPU1VCPU0(HLT-ed)kvm_sched_intimereturnfromschedule()inkvm_vcpu_block()kvm_vcpu_kick21VMRESUMEvmx_vcpu_runkvm_vcpu_kickKVMHLTInternalsSoKVMisslowatdeliveringIPIsand/orcomingoutofHLT.
ButwhyPossibleculprits:WRMSRIPIISRVMEXITVCPU1VCPU0(HLT-ed)kvm_sched_intimereturnfromschedule()inkvm_vcpu_block()22RDTSCRDTSCRDTSCRDTSCRDTSCKVMHLTInternalsWRMSRkvm_vcpu_kickreturnfromschedule()inkvm_vcpu_block()vmx_vcpu_runIPIISRVMEXITVMRESUMEMin(cycles):400600730032001300VCPU1VCPU0guesthostVT-xKVMSchedulerkvm_sched_in:4924001200850034001400Median(cycles):23Unsurprisingly,theschedulertakessometimetoruntheVCPUSlowevenintheuncontended,cache-hot,case.
ImagineiftheVCPUiscontendingforCPUtimewithotherthreads.
Experiment:Don'tscheduleonHLT.
JustpollfortheIPIinkvm_vcpu_block.
KVMHLTInternals24Whathappenswhenyoudon'tscheduleonHLTKVM(Alwaysschedule)5.
7usKVM(Neverschedule)1.
7usHardware(SandyBridge)0.
5usNeverschedule!
CyclesKVM(Alwaysschedule)KVM(Neverschedule)HardwareMin1380040001200Average158004400120050%ile149004300120090%ile160004500130099%ile2490069001300Max52100050000140025SimilarimprovementsonIvyBridge(5.
6us->1.
6us)Haswell(4.
9us->1.
5us).
Neverschedule!
WRMSRkvm_vcpu_kickreturnfromschedule()inkvm_vcpu_block()vmx_vcpu_runIPIISRVMEXITVMRESUMEAlwaysschedule:4001200850034001400VCPU1VCPU0guesthostVT-xKVMSchedulerNeverschedule:300130011004001200(mediancycles)26Neverschedule!
WeeliminatealmostallofthelatencyoverheadbynotschedulingonHLT.
Schedulingisoftentherightthingtodo.
LetotherthreadsrunorsavehostCPUpower.
Mostofthetimeimprovesguestperformance(lettheIOthreadsrun!
).
Canhurtperformance.
Seemicrobenchmark.
SeeTCP_RR.
27Halt-PollingStep1:PollForuptoXnanoseconds:IfataskiswaitingtorunonourCPU,gotoStep2.
Checkifaguestinterruptarrived.
Ifso,wearedone.
Repeat.
Step2:schedule()Scheduleoutuntilit'stimetocomeoutofHLT.
Pros:WorksonshortHLTs(Cons:IncreasesCPUusage(~1%foridleVCPUsifX=200,000ns)Doesnotappeartonegativelyaffectturboofactivecores.
28Halt-PollingMemcache:1.
5xlatencyimprovementWindowsEventObjects:2xlatencyimprovementReducemessagepassinglatencyby10-15us(includingnetworklatency).
29Halt-PollingMergedintothe4.
0kernel[PATCH]kvm:addhalt_poll_nsmoduleparameterThankstoPaoloBonziniUsetheKVMmoduleparameterhalt_poll_nstocontrolhowlongtopolloneachHLT.
Futureimprovements:Automaticpolltoggling(removeidleCPUoverheadbyturningpollingoff).
Automatichalt_poll_nsKVMwillset(andvary)halt_poll_nsdynamically.
Howtodothisisanopenquestion.
.
.
ideasLazyContextSwitchingEquivalentfeature,butavailableforanykernelcomponenttouse.
30ConclusionMessagePassingEvenloopbackmessagepassingrequiresvirtualization.
Beingidle(asaLinuxguest)requiresvirtualization.
Cross-CPUcommunicationrequiresvirtualization.
Halt-Pollingsaves10-15usonmessagepassinground-triplatency.
Remaininground-triplatency:4MSRwritestotheAPICtimer(3-5us)IPIsend(~2us)HLTwakeup(evenwithhalt-polling,stilladds~3us!
)31

趣米云月付460元,香港CN2云服务器VPS月付低至18元

趣米云早期为做技术起家,为3家IDC提供技术服务2年多,目前商家在售的服务有香港vps、香港独立服务器、香港站群服务器等,线路方面都是目前最优质的CN2,直连大陆,延时非常低,适合做站,目前商家正在做七月优惠活动,VPS低至18元,价格算是比较便宜的了。趣米云vps优惠套餐:KVM虚拟架构,香港沙田机房,线路采用三网(电信,联通,移动)回程电信cn2、cn2 gia优质网络,延迟低,速度快。自行封...

提速啦(900元/月),杭州BGP E5-2665/89*2 32核 48G 100G防御

提速啦的来历提速啦是 网站 本着“良心 便宜 稳定”的初衷 为小白用户避免被坑提速啦的市场定位提速啦主要代理市场稳定速度的云服务器产品,避免新手购买云服务器的时候众多商家不知道如何选择,妮妮云就帮你选择好了产品,无需承担购买风险,不用担心出现被跑路 被诈骗的情况。提速啦的售后保证提速啦退款 通过于合作商的友好协商,云服务器提供3天内全额退款,超过3天不退款 物理机部分支持当天全额退款提速啦提现 充...

PacificRack:洛杉矶KVM月付1.5美元起,1G内存套餐年付12美元起

PacificRack在本月发布了几款特价产品,其中最低款支持月付仅1.5美元,基于KVM架构,洛杉矶机房,PR-M系列。PacificRack简称PR,QN机房旗下站点,主要提供低价VPS主机产品,基于KVM架构,数据中心为自营洛杉矶机房,现在只有PR-M一个系列,分为了2个类别:常规(Elastic Compute Service)和多IP产品(Multi IP Server)。下面列出几款秒...

ivybridge为你推荐
阿丽克丝·布莱肯瑞吉阿丽克斯布莱肯瑞吉演的美国恐怖故事哪两集access数据库什么是ACCESS数据库同ip网站查询服务器禁PING 是不是就可以解决同IP网站查询问题7788k.com以前有个网站是7788MP3.com后来改成KK130现在又改网站域名了。有知道现在是什么域名么?地陷裂口天上顿时露出一个大窟窿地上也裂开了,一到黑幽幽的深沟可以用什么四字词语来?www.119mm.comwww.993mm+com精品集!336.com求那个网站 你懂得 1552517773@qqwww.baitu.com韩国片爱人.欲望的观看地址dadi.tvapple TV 功能介绍www.15job.com南方人才市场有官方网站是什么?
过期域名 美国服务器租用 出租服务器 工信部域名备案系统 technetcal 便宜服务器 blackfriday cdn服务器 视频存储服务器 免备案空间 bash漏洞 香港新世界电讯 天猫双十一秒杀 免费个人博客 发包服务器 qq数据库下载 网站木马检测工具 老左正传 域名接入 国外代理服务器地址 更多