Re: Some Code for Performance Profiling
2010/4/5 Avi Kivity a...@redhat.com: On 03/31/2010 07:53 PM, Jiaqing Du wrote: Hi, We have some code about performance profiling in KVM. They are outputs of a school project. Previous discussions in KVM, Perfmon2, and Xen mailing lists helped us a lot. The code are NOT in a good shape and are only used to demonstrated the feasibility of doing performance profiling in KVM. Feel free to use it if you want. Performance monitoring is an important feature for kvm. Is there any chance you can work at getting it into good shape? I have been following the discussions about PMU virtualization in the list for a while. Exporting a proper interface, i.e., guest visible MSRs and supported events, to the guest across a large number physical CPUs from different vendors, families, and models is the major problem. For KVM, currently it also supports almost a dozen different types of virtual CPUs. I will think about it and try to come up with something more general. We categorize performance profiling in a virtualized environment into two types: *guest-wide profiling* and *system-wide profiling*. For guest-wide profiling, only the guest is profiled. KVM virtualizes the PMU and the user runs a profiler directly in the guest. It requires no modifications to the guest OS and the profiler running in the guest. For system-wide profiling, both KVM and the guest OS are profiled. The results are similar to what XenOprof outputs. In this case, one profiler running in the host and one profiler running in the guest. Still it requires no modifications to the guest and the profiler running in it. Can your implementation support both simultaneously? What do you mean simultaneously? With my implementation, you either do guest-wide profiling or system-wide profiling. They are achieved through different patches. Actually, the result of guest-wide profiling is a subset of system-wide profiling. For guest-wide profiling, there are two possible places to save and restore the related MSRs. One is where the CPU switches between guest mode and host mode. We call this *CPU-switch*. Profiling with this enabled reflects how the guest behaves on the physical CPU, plus other virtualized, not emulated, devices. The other place is where the CPU switches between the KVM context and others. Here KVM context means the CPU is executing guest code or KVM code, both kernel space and user space. We call this *domain-switch*. Profiling with this enabled discloses how the guest behaves on both the physical CPU and KVM. (Some emulated operations are really expensive in a virtualized environment.) Which method do you use? Or do you support both? I post two patches in my previous email. One is for CPU-switch, and the other is for domain-switch. Note disclosing host pmu data to the guest is sometimes a security issue. For instance? -- Do not meddle in the internals of kernels, for they are subtle and quick to panic. -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Some Code for Performance Profiling
On 04/07/2010 10:23 PM, Jiaqing Du wrote: Can your implementation support both simultaneously? What do you mean simultaneously? With my implementation, you either do guest-wide profiling or system-wide profiling. They are achieved through different patches. Actually, the result of guest-wide profiling is a subset of system-wide profiling. A guest admin monitors the performance of their guest via a vpmu. Meanwhile the host admin monitors the performance of the host (including all guests) using the host pmu. Given that the host pmu and the vpmu may select different counters, it is difficult to support both simultaneously. For guest-wide profiling, there are two possible places to save and restore the related MSRs. One is where the CPU switches between guest mode and host mode. We call this *CPU-switch*. Profiling with this enabled reflects how the guest behaves on the physical CPU, plus other virtualized, not emulated, devices. The other place is where the CPU switches between the KVM context and others. Here KVM context means the CPU is executing guest code or KVM code, both kernel space and user space. We call this *domain-switch*. Profiling with this enabled discloses how the guest behaves on both the physical CPU and KVM. (Some emulated operations are really expensive in a virtualized environment.) Which method do you use? Or do you support both? I post two patches in my previous email. One is for CPU-switch, and the other is for domain-switch. I see. I'm not sure I know which one is better! Note disclosing host pmu data to the guest is sometimes a security issue. For instance? The standard example is hyperthreading where the memory bus unit is shared among two logical processors. A guest sampling a vcpu on one thread can gain information about what is happening on the other - the number of bus transactions the other thread has issued. This can be used to establish a communication channel between two guests that shouldn't be communicating, or to eavesdrop on another guest. A similar problem happens with multicores. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain. -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Some Code for Performance Profiling
On 03/31/2010 07:53 PM, Jiaqing Du wrote: Hi, We have some code about performance profiling in KVM. They are outputs of a school project. Previous discussions in KVM, Perfmon2, and Xen mailing lists helped us a lot. The code are NOT in a good shape and are only used to demonstrated the feasibility of doing performance profiling in KVM. Feel free to use it if you want. Performance monitoring is an important feature for kvm. Is there any chance you can work at getting it into good shape? We categorize performance profiling in a virtualized environment into two types: *guest-wide profiling* and *system-wide profiling*. For guest-wide profiling, only the guest is profiled. KVM virtualizes the PMU and the user runs a profiler directly in the guest. It requires no modifications to the guest OS and the profiler running in the guest. For system-wide profiling, both KVM and the guest OS are profiled. The results are similar to what XenOprof outputs. In this case, one profiler running in the host and one profiler running in the guest. Still it requires no modifications to the guest and the profiler running in it. Can your implementation support both simultaneously? For guest-wide profiling, there are two possible places to save and restore the related MSRs. One is where the CPU switches between guest mode and host mode. We call this *CPU-switch*. Profiling with this enabled reflects how the guest behaves on the physical CPU, plus other virtualized, not emulated, devices. The other place is where the CPU switches between the KVM context and others. Here KVM context means the CPU is executing guest code or KVM code, both kernel space and user space. We call this *domain-switch*. Profiling with this enabled discloses how the guest behaves on both the physical CPU and KVM. (Some emulated operations are really expensive in a virtualized environment.) Which method do you use? Or do you support both? Note disclosing host pmu data to the guest is sometimes a security issue. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic. -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
