Re: [libvirt] [RFC PATCHv2 00/10] x86 RDT Cache Monitoring Technology (CMT)

> -----Original Message----- > From: Martin Kletzander [mailto:mkletzan@redhat.com] > Sent: Tuesday, July 17, 2018 5:11 PM > To: Wang, Huaqiang <huaqiang.wang(a)intel.com&gt; > Cc: libvir-list(a)redhat.com; Feng, Shaohe <shaohe.feng(a)intel.com>; Niu, Bing > <bing.niu(a)intel.com>; Ding, Jian-feng <jian-feng.ding(a)intel.com>; Zang, Rui > <rui.zang(a)intel.com&gt; > Subject: Re: [libvirt] [RFC PATCHv2 00/10] x86 RDT Cache Monitoring > Technology (CMT) > > On Tue, Jul 17, 2018 at 07:19:41AM +0000, Wang, Huaqiang wrote: > >Hi Martin, > > > >Thanks for your comments. Please see my reply inline. > > > >> -----Original Message----- > >> From: Martin Kletzander [mailto:mkletzan@redhat.com] > >> Sent: Tuesday, July 17, 2018 2:27 PM > >> To: Wang, Huaqiang <huaqiang.wang(a)intel.com&gt; > >> Cc: libvir-list(a)redhat.com; Feng, Shaohe <shaohe.feng(a)intel.com>; > >> Niu, Bing <bing.niu(a)intel.com>; Ding, Jian-feng > >> <jian-feng.ding(a)intel.com>; Zang, Rui <rui.zang(a)intel.com&gt; > >> Subject: Re: [libvirt] [RFC PATCHv2 00/10] x86 RDT Cache Monitoring > >> Technology (CMT) > >> > >> On Mon, Jul 09, 2018 at 03:00:48PM +0800, Wang Huaqiang wrote: > >> > > >> >This is the V2 of RFC and the POC source code for introducing x86 > >> >RDT CMT feature, thanks Martin Kletzander for his review and > >> >constructive suggestion for V1. > >> > > >> >This series is trying to provide the similar functions of the perf > >> >event based CMT, MBMT and MBML features in reporting cache > >> >occupancy, total memory bandwidth utilization and local memory > >> >bandwidth utilization information in livirt. Firstly we focus on cmt. > >> > > >> >x86 RDT Cache Monitoring Technology (CMT) provides a medthod to > >> >track the cache occupancy information per CPU thread. We are > >> >leveraging the implementation of kernel resctrl filesystem and > >> >create our patches on top of that. > >> > > >> >Describing the functionality from a high level: > >> > > >> >1. Extend the output of 'domstats' and report CMT inforamtion. > >> > > >> >Comparing with perf event based CMT implementation in libvirt, this > >> >series extends the output of command 'domstat' and reports cache > >> >occupancy information like these: > >> ><pre> > >> >[root@dl-c200 libvirt]# virsh domstats vm3 --cpu-resource > >> >Domain: 'vm3' > >> > cpu.cacheoccupancy.vcpus_2.value=4415488 > >> > cpu.cacheoccupancy.vcpus_2.vcpus=2 > >> > cpu.cacheoccupancy.vcpus_1.value=7839744 > >> > cpu.cacheoccupancy.vcpus_1.vcpus=1 > >> > cpu.cacheoccupancy.vcpus_0,3.value=53796864 > >> > cpu.cacheoccupancy.vcpus_0,3.vcpus=0,3 > >> ></pre> > >> >The vcpus have been arragned into three monitoring groups, these > >> >three groups cover vcpu 1, vcpu 2 and vcpus 0,3 respectively. Take > >> >an example, the 'cpu.cacheoccupancy.vcpus_0,3.value' reports the > >> >cache occupancy information for vcpu 0 and vcpu 3, the > >> 'cpu.cacheoccupancy.vcpus_0,3.vcpus' > >> >represents the vcpu group information. > >> > > >> >To address Martin's suggestion "beware as 1-4 is something else than > >> >1,4 so you need to differentiate that.", the content of 'vcpus' > >> >(cpu.cacheoccupancy.<groupname>.vcpus=xxx) has been specially > >> >processed, if vcpus is a continous range, e.g. 0-2, then the output > >> >of cpu.cacheoccupancy.vcpus_0-2.vcpus will be like > >> >'cpu.cacheoccupancy.vcpus_0-2.vcpus=0,1,2' > >> >instead of > >> >'cpu.cacheoccupancy.vcpus_0-2.vcpus=0-2'. > >> >Please note that 'vcpus_0-2' is a name of this monitoring group, > >> >could be specified any other word from the XML configuration file or > >> >lively changed with the command introduced in following part. > >> > > >> > >> One small nit according to the naming (but it shouldn't block any > >> reviewers from reviewing, just keep this in mind for next version for > >> example) is that this is still inconsistent. > > > >OK. I'll try to use words such as 'cache', 'cpu resource' and avoid > >using 'RDT', 'CMT'. > > > > Oh, you misunderstood, I meant the naming in the domstats output =) > > >The way domstats are structured when there is something like an > >> array could shed some light into this. What you suggested is really > >> kind of hard to parse (although looks better). What would you say to > something like this: > >> > >> cpu.cacheoccupancy.count = 3 > >> cpu.cacheoccupancy.0.value=4415488 > >> cpu.cacheoccupancy.0.vcpus=2 > >> cpu.cacheoccupancy.0.name=vcpus_2 > >> cpu.cacheoccupancy.1.value=7839744 > >> cpu.cacheoccupancy.1.vcpus=1 > >> cpu.cacheoccupancy.1.name=vcpus_1 > >> cpu.cacheoccupancy.2.value=53796864 > >> cpu.cacheoccupancy.2.vcpus=0,3 > >> cpu.cacheoccupancy.2.name=0,3 > >> > > > >Your arrangement looks more reasonable, thanks for your advice. > >However, as I mentioned in another email that I sent to libvirt-list > >hours ago, the kernel resctrl interface provides cache occupancy > >information for each cache block for every resource group. > >Maybe we need to expose the cache occupancy for each cache block. > >If you agree, we need to refine the 'domstats' output message, how > >about this: > > > > cpu.cacheoccupancy.count=3 > > cpu.cacheoccupancy.0.name=vcpus_2 > > cpu.cacheoccupancy.0.vcpus=2 > > cpu.cacheoccupancy.0.block.count=2 > > cpu.cacheoccupancy.0.block.0.bytes=5488 > > cpu.cacheoccupancy.0.block.1. bytes =4410000 > > cpu.cacheoccupancy.1.name=vcpus_1 > > cpu.cacheoccupancy.1.vcpus=1 > > cpu.cacheoccupancy.1.block.count=2 > > cpu.cacheoccupancy.1.block.0. bytes =7839744 > > cpu.cacheoccupancy.1.block.0. bytes =0 > > cpu.cacheoccupancy.2.name=0,3 > > cpu.cacheoccupancy.2.vcpus=0,3 > > cpu.cacheoccupancy.2.block.count=2 > > cpu.cacheoccupancy.2.block.0. bytes=53796864 > > cpu.cacheoccupancy.2.block.1. bytes=0 > > > > What do you mean by cache block? Is that (cache_size / granularity)? In that > case it looks fine, I guess (without putting too much thought into it). No. 'cache block' that I mean is indexed with 'cache id', with the id number kept in '/sys/devices/system/cpu/cpu*/cache/index*/id'. Generally for a two socket server node, there are two sockets (with CPU E5-2680 v4, for example) in system, and each socket has a L3 cache, if resctrl monitoring group is created (/sys/fs/resctrl/p0, for example), you can find the cache occupancy information for these two L3 cache areas separately from file /sys/fs/resctrl/p0/mon_data/mon_L3_00/llc_occupancy and file /sys/fs/resctrl/p0/mon_data/mon_L3_01/llc_occupancy Cache information for individual socket is meaningful to detect performance issues such as workload balancing...etc. We'd better expose these details to libvirt users. To my knowledge, I am using 'cache block' to describe the CPU cache indexed with number found in '/sys/devices/system/cpu/cpu*/cache/index*/id'. I welcome suggestion on other kind of naming for it.

> > Martin