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.

>> Martin