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

> -----Original Message----- > From: Martin Kletzander [mailto:mkletzan@redhat.com] > Sent: Wednesday, July 18, 2018 8:07 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 Wed, Jul 18, 2018 at 02:29:32AM +0000, Wang, Huaqiang wrote: > > > > > >> -----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. > > > > To be consistent I'd prefer "cache" "cache bank" and "index" or "id". I don't > have specific requirements, I just don't want to invent new words. Look at how > it is described in capabilities for example. > Make sense. Then let's use 'id' for the the purpose, and the output would be: cpu.cacheoccupancy.count=3 cpu.cacheoccupancy.0.name=vcpus_2 cpu.cacheoccupancy.0.vcpus=2 cpu.cacheoccupancy.0.id.count=2 cpu.cacheoccupancy.0.id.0.bytes=5488 cpu.cacheoccupancy.0.id.1.bytes =4410000 cpu.cacheoccupancy.1.name=vcpus_1 cpu.cacheoccupancy.1.vcpus=1 cpu.cacheoccupancy.1.id.count=2 cpu.cacheoccupancy.1.id.0.bytes =7839744 cpu.cacheoccupancy.1.id.1.bytes =0 cpu.cacheoccupancy.2.name=0,3 cpu.cacheoccupancy.2.vcpus=0,3 cpu.cacheoccupancy.2.id.count=2 cpu.cacheoccupancy.2.id.0.bytes=53796864 cpu.cacheoccupancy.2.id.1.bytes=0 How about it?