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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Questions about Using Perf at Dom0
On 08/29/2016 08:12 PM, Sanghyun Hong wrote: > Hi Boris, > > /[Appreciate for your support, and I have one last question]/ > > Since we’re using the */Xen/* hypervisor (not the KVM that is > type-II), I think we cannot use the /*perf k*/*/vm/* command. Here are > the outputs: > > -------- > # perf kvm --host --guest record -C 1 sleep 1 > [ perf record: Woken up 1 times to write data ] > Warning: > 1 unprocessable samples recorded. > Do you have a KVM guest running and not using 'perf kvm'? > [ perf record: Captured and wrote 0.242 MB perf.data.kvm ] As I said, this works for me for Xen guests. I thought perf kvm might check whether there is a KVM guest but it's not. The error message that you see is generated at the end of sampling if no samples are found. What Xen and Linux versions are you running (xl info)? Do you know whether performance counters are enabled (dmesg | grep Performance)? > > # perf kvm --guest --host report --stdio > Warning: > 1 unprocessable samples recorded. > Do you have a KVM guest running and not using 'perf kvm'? > Error: > The perf.data.kvm file has no samples! > # To display the perf.data header info, please use > --header/--header-only options. > # > -------- > > In addition, we used perf to collect hardware performance counters, > not the symbols, kernel functions, or other stuffs. Symbols are added to samples at the end --- perf doesn't collect them explicitly. > Thus, what we really need is that we need to separate the hardware > counters by each domain if it’s possible (i.e. we want to verify some > counters are from Dom0, other counters are from Dom1, and the others > come from Dom2, etc.) > > I’m pretty much sure that the code you used to distinguish each domain > from samples will work. I wonder if you can agree with that. It does work. Note though that you will only be able distinguish dom0 from guests, i.e. all non-dom0 guests are presented by perf as a single guest, you won't be able to separate guest1 from guest2. I don't know whether this is perf kvm limitation or (more likely) something specific to perf kvm processing samples from Xen. I've never looked at that. -boris > > Best, > Sanghyun. > > >> On Aug 29, 2016, at 6:37 PM, Boris Ostrovsky >> <boris.ostrovsky@xxxxxxxxxx <mailto:boris.ostrovsky@xxxxxxxxxx>> wrote: >> >> On 08/29/2016 05:48 PM, Sanghyun Hong wrote: >>> I really appreciate for your answers. Last but not the least, I want >>> to make it more clear: >>> >>>> The hypervisor will provide dom0 with a raw sample (guest's, dom0's or >>>> hypervisor's) and then it's the job of dom0 kernel to properly tag and >>>> format it and make it available to the userland (i.e. perf itself). >>> Does this mean if I run the perf command on Dom0 while other domains >>> are running, we can collect the performance counter values without >>> distinguishing each domain, right? >> >> With 'self' mode each domain collects samples only for itself. >> >> And for 'all' mode apparently this kind of works. With perf build from >> Linux 4.7 tree: >> >> root@haswell> xl vcpu-list >> Name ID VCPU CPU State Time(s) >> Affinity (Hard / Soft) >> Domain-0 0 0 0 -b- 55.0 0 >> / all >> Domain-0 0 1 1 r-- 35.9 1 >> / all >> Domain-0 0 2 2 -b- 36.9 2 >> / all >> Domain-0 0 3 3 -b- 36.2 3 >> / all >> fedora 1 0 1 -b- 183.7 1 >> / all >> root@haswell> ./perf kvm --guest --host --guestkallsyms=/tmp/kallsyms >> record -C 1 sleep 1 >> [ perf record: Woken up 1 times to write data ] >> [ perf record: Captured and wrote 0.139 MB perf.data.kvm (60 samples) ] >> root@haswell> ./perf kvm --guest --host --guestkallsyms=/tmp/kallsyms >> report --stdio >> ... >> # Overhead Command Shared Object >> Symbol >> # ........ ............... ....................... >> ............................................. >> # >> 14.48% swapper [unknown] [k] >> 0xffff82d0801c7a37 >> 6.06% swapper [kernel.kallsyms] [k] >> update_blocked_averages >> 4.38% swapper [unknown] [k] >> 0xffff82d08013690f >> 2.75% swapper [kernel.kallsyms] [k] update_rq_clock >> 2.34% swapper [kernel.kallsyms] [k] irq_enter >> 2.33% [guest/0] [guest.kernel.kallsyms] [g] >> fb_pad_aligned_buffer >> 2.24% 1.hda-0 [kernel.kallsyms] [k] >> _raw_spin_unlock_irqrestore >> 2.11% [guest/0] [guest.kernel.kallsyms] [g] native_safe_halt >> 2.05% [guest/0] [guest.kernel.kallsyms] [g] >> update_blocked_averages >> ... >> >> "unknown" samples are from hypervisor. >> >> >>> >>>> The tool will then look at the tag and display the event as >>>> belonging to >>>> host (dom0, really) or guest. This is supported for KVM, with 'perf >>>> kvm' >>>> commands. >>>> >>>> So if you can run perf kvm commands then you may be able to >>>> differentiate dom0's and guest's samples (you will also see hypervisor >>>> samples but they won't get resolved to symbols). I am just not sure per >>>> kvm will run on a non-KVM host. I had a private copy where it did but >>>> this was based on a fairly old version of Linux. >>>> >>>> (Also, stack profiling is not supported at all). >>> >>> I wonder if you can share the private copy of your code. I’m looking >>> into the source code of the patches, and it seems there’s a way to >>> do it. Even if your codes are outdated, I think I can manage to port >>> it. I will promise once I finish the porting, I will share my >>> adjustment of your code as well. >> >> Looks like you may not need it. >> >> -boris >> >>> >>> Best, >>> Sanghyun. >>> >>> >>>> On Aug 29, 2016, at 5:24 PM, Boris Ostrovsky >>>> <boris.ostrovsky@xxxxxxxxxx <mailto:boris.ostrovsky@xxxxxxxxxx>> wrote: >>>> >>>> On 08/29/2016 05:08 PM, Sanghyun Hong wrote: >>>>>> Yes, this will allow the hypervisor to collect samples from multiple >>>>>> guests. However, the tool (perf) probably won't be able to properly >>>>>> process these samples. But you can try. >>>>> I understand, thus, I applied the patches and set >>>>> the /pmu_mode/ to *all*. However, I’m really curious what you mean by >>>>> the tool (*perf*) probably won’t be able to properly process these >>>>> samples. Is there any things I have to have in mind while collecting >>>>> the counters, or will it have incorrect values of the counters? >>>> The hypervisor will provide dom0 with a raw sample (guest's, dom0's or >>>> hypervisor's) and then it's the job of dom0 kernel to properly tag and >>>> format it and make it available to the userland (i.e. perf itself). The >>>> tool will then look at the tag and display the event as belonging to >>>> host (dom0, really) or guest. This is supported for KVM, with 'perf >>>> kvm' >>>> commands. >>>> >>>> So if you can run perf kvm commands then you may be able to >>>> differentiate dom0's and guest's samples (you will also see hypervisor >>>> samples but they won't get resolved to symbols). I am just not sure per >>>> kvm will run on a non-KVM host. I had a private copy where it did but >>>> this was based on a fairly old version of Linux. >>>> >>>> (Also, stack profiling is not supported at all). >>>> >>>>>> You will want to run dom0 on all physical processors (i.e. no >>>>>> dom0_max_vcpus boot option) and pin all VCPUs for both dom0 and the >>>>>> guest. >>>>> Sure, thanks! My machine has four physical cores, and I’ve set >>>>> the /dom0_max_vcpus=4/. I think it will have the same effect in >>>>> removing the /dom0_max_vcpus/ option. >>>> Yes. >>>> >>>> -boris >>>> >>>>> Best, >>>>> Sanghyun. >>>>> >>>>> >>>>>> On Aug 29, 2016, at 4:59 PM, Boris Ostrovsky >>>>>> <boris.ostrovsky@xxxxxxxxxx <mailto:boris.ostrovsky@xxxxxxxxxx> >>>>>> <mailto:boris.ostrovsky@xxxxxxxxxx>> wrote: >>>>>> >>>>>> On 08/29/2016 02:42 PM, Sanghyun Hong wrote: >>>>>>> Hi Boris, >>>>>>> >>>>>>> I’ve found the >>>>>>> documentations(https://github.com/torvalds/linux/blob/master/Documentation/ABI/testing/sysfs-hypervisor-pmu) >>>>>>> in the kernel source code, and it seems like if we change the mode >>>>>>> from *self* to *all* then we can collect counters for all the >>>>>>> domains, >>>>>>> right? >>>>>> Yes, this will allow the hypervisor to collect samples from multiple >>>>>> guests. However, the tool (perf) probably won't be able to properly >>>>>> process these samples. But you can try. >>>>>> >>>>>> You will want to run dom0 on all physical processors (i.e. no >>>>>> dom0_max_vcpus boot option) and pin all VCPUs for both dom0 and the >>>>>> guest. >>>>>> >>>>>> >>>>>> -boris >>>>>> >>>>>>> All the best, >>>>>>> Sanghyun. >>>>>>> >>>>>>> >>>>>>>> On Aug 29, 2016, at 12:36 PM, Boris Ostrovsky >>>>>>>> <boris.ostrovsky@xxxxxxxxxx <mailto:boris.ostrovsky@xxxxxxxxxx> >>>>>>>> <mailto:boris.ostrovsky@xxxxxxxxxx> >>>>>>>> <mailto:boris.ostrovsky@xxxxxxxxxx>> wrote: >>>>>>>> >>>>>>>> On 08/29/2016 09:18 AM, Sanghyun Hong wrote: >>>>>>>>> Dear Xen-Devel Community: >>>>>>>>> >>>>>>>>> I’m a grad student working on measuring performance counters >>>>>>>>> at the >>>>>>>>> Xen domains. I read this >>>>>>>>> thread(https://wiki.xenproject.org/wiki/Xen_Profiling:_oprofile_and_perf) >>>>>>>>> in >>>>>>>>> web, and it says using Linux perf command will let us collecting >>>>>>>>> performance counters in both dom0 and domU. Does it mean that >>>>>>>>> we can >>>>>>>>> collect both of them at once if we run perf command on the >>>>>>>>> dom0? (If >>>>>>>>> not, does it mean we can collect counters for each domain >>>>>>>>> separately >>>>>>>>> once we run the perf command in each domain? >>>>>>>> Profiling both guest and dom0 (and the hypervisor) requires >>>>>>>> changes to >>>>>>>> perf and those are not there yet. >>>>>>>> >>>>>>>> But you can run perf in each guest (including dom0) separately. >>>>>>>> Make >>>>>>>> sure you have vpmu=true boot option. >>>>>>>> >>>>>>>> -boris > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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