Hi Reinette, On Thu, Feb 20, 2025 at 7:36 PM Reinette Chatre <reinette.chatre@xxxxxxxxx> wrote: > > Hi Peter, > > On 2/20/25 6:53 AM, Peter Newman wrote: > > Hi Reinette, > > > > On Wed, Feb 19, 2025 at 7:21 PM Reinette Chatre > > <reinette.chatre@xxxxxxxxx> wrote: > >> > >> Hi Peter, > >> > >> On 2/19/25 3:28 AM, Peter Newman wrote: > >>> Hi Reinette, > >>> > >>> On Tue, Feb 18, 2025 at 6:50 PM Reinette Chatre > >>> <reinette.chatre@xxxxxxxxx> wrote: > >>>> > >>>> Hi Peter, > >>>> > >>>> On 2/17/25 2:26 AM, Peter Newman wrote: > >>>>> Hi Reinette, > >>>>> > >>>>> On Fri, Feb 14, 2025 at 8:18 PM Reinette Chatre > >>>>> <reinette.chatre@xxxxxxxxx> wrote: > >>>>>> > >>>>>> Hi Babu, > >>>>>> > >>>>>> On 2/14/25 10:31 AM, Moger, Babu wrote: > >>>>>>> On 2/14/2025 12:26 AM, Reinette Chatre wrote: > >>>>>>>> On 2/13/25 9:37 AM, Dave Martin wrote: > >>>>>>>>> On Wed, Feb 12, 2025 at 03:33:31PM -0800, Reinette Chatre wrote: > >>>>>>>>>> On 2/12/25 9:46 AM, Dave Martin wrote: > >>>>>>>>>>> On Wed, Jan 22, 2025 at 02:20:08PM -0600, Babu Moger wrote: > >>>>>> > >>>>>> (quoting relevant parts with goal to focus discussion on new possible syntax) > >>>>>> > >>>>>>>>>> I see the support for MPAM events distinct from the support of assignable counters. > >>>>>>>>>> Once the MPAM events are sorted, I think that they can be assigned with existing interface. > >>>>>>>>>> Please help me understand if you see it differently. > >>>>>>>>>> > >>>>>>>>>> Doing so would need to come up with alphabetical letters for these events, > >>>>>>>>>> which seems to be needed for your proposal also? If we use possible flags of: > >>>>>>>>>> > >>>>>>>>>> mbm_local_read_bytes a > >>>>>>>>>> mbm_local_write_bytes b > >>>>>>>>>> > >>>>>>>>>> Then mbm_assign_control can be used as: > >>>>>>>>>> # echo '//0=ab;1=b' >/sys/fs/resctrl/info/L3_MON/mbm_assign_control > >>>>>>>>>> # cat /sys/fs/resctrl/mon_data/mon_L3_00/mbm_local_read_bytes > >>>>>>>>>> <value> > >>>>>>>>>> # cat /sys/fs/resctrl/mon_data/mon_L3_00/mbm_local_bytes > >>>>>>>>>> <sum of mbm_local_read_bytes and mbm_local_write_bytes> > >>>>>>>>>> > >>>>>>>>>> One issue would be when resctrl needs to support more than 26 events (no more flags available), > >>>>>>>>>> assuming that upper case would be used for "shared" counters (unless this interface is defined > >>>>>>>>>> differently and only few uppercase letters used for it). Would this be too low of a limit? > >>>>>> > >>>>>> As mentioned above, one possible issue with existing interface is that > >>>>>> it is limited to 26 events (assuming only lower case letters are used). The limit > >>>>>> is low enough to be of concern. > >>>>> > >>>>> The events which can be monitored by a single counter on ABMC and MPAM > >>>>> so far are combinable, so 26 counters per group today means it limits > >>>>> breaking down MBM traffic for each group 26 ways. If a user complained > >>>>> that a 26-way breakdown of a group's MBM traffic was limiting their > >>>>> investigation, I would question whether they know what they're looking > >>>>> for. > >>>> > >>>> The key here is "so far" as well as the focus on MBM only. > >>>> > >>>> It is impossible for me to predict what we will see in a couple of years > >>>> from Intel RDT, AMD PQoS, and Arm MPAM that now all rely on resctrl interface > >>>> to support their users. Just looking at the Intel RDT spec the event register > >>>> has space for 32 events for each "CPU agent" resource. That does not take into > >>>> account the "non-CPU agents" that are enumerated via ACPI. Tony already mentioned > >>>> that he is working on patches [1] that will add new events and shared the idea > >>>> that we may be trending to support "perf" like events associated with RMID. I > >>>> expect AMD PQoS and Arm MPAM to provide related enhancements to support their > >>>> customers. > >>>> This all makes me think that resctrl should be ready to support more events than 26. > >>> > >>> I was thinking of the letters as representing a reusable, user-defined > >>> event-set for applying to a single counter rather than as individual > >>> events, since MPAM and ABMC allow us to choose the set of events each > >>> one counts. Wherever we define the letters, we could use more symbolic > >>> event names. > >> > >> Thank you for clarifying. > >> > >>> > >>> In the letters as events model, choosing the events assigned to a > >>> group wouldn't be enough information, since we would want to control > >>> which events should share a counter and which should be counted by > >>> separate counters. I think the amount of information that would need > >>> to be encoded into mbm_assign_control to represent the level of > >>> configurability supported by hardware would quickly get out of hand. > >>> > >>> Maybe as an example, one counter for all reads, one counter for all > >>> writes in ABMC would look like... > >>> > >>> (L3_QOS_ABMC_CFG.BwType field names below) > >>> > >>> (per domain) > >>> group 0: > >>> counter 0: LclFill,RmtFill,LclSlowFill,RmtSlowFill > >>> counter 1: VictimBW,LclNTWr,RmtNTWr > >>> group 1: > >>> counter 2: LclFill,RmtFill,LclSlowFill,RmtSlowFill > >>> counter 3: VictimBW,LclNTWr,RmtNTWr > >>> ... > >>> > >> > >> I think this may also be what Dave was heading towards in [2] but in that > >> example and above the counter configuration appears to be global. You do mention > >> "configurability supported by hardware" so I wonder if per-domain counter > >> configuration is a requirement? > > > > If it's global and we want a particular group to be watched by more > > counters, I wouldn't want this to result in allocating more counters > > for that group in all domains, or allocating counters in domains where > > they're not needed. I want to encourage my users to avoid allocating > > monitoring resources in domains where a job is not allowed to run so > > there's less pressure on the counters. > > > > In Dave's proposal it looks like global configuration means > > globally-defined "named counter configurations", which works because > > it's really per-domain assignment of the configurations to however > > many counters the group needs in each domain. > > I think I am becoming lost. Would a global configuration not break your > view of "event-set applied to a single counter"? If a counter is configured > globally then it would not make it possible to support the full configurability > of the hardware. > Before I add more confusion, let me try with an example that builds on your > earlier example copied below: > > >>> (per domain) > >>> group 0: > >>> counter 0: LclFill,RmtFill,LclSlowFill,RmtSlowFill > >>> counter 1: VictimBW,LclNTWr,RmtNTWr > >>> group 1: > >>> counter 2: LclFill,RmtFill,LclSlowFill,RmtSlowFill > >>> counter 3: VictimBW,LclNTWr,RmtNTWr > >>> ... > > Since the above states "per domain" I rewrite the example to highlight that as > I understand it: > > group 0: > domain 0: > counter 0: LclFill,RmtFill,LclSlowFill,RmtSlowFill > counter 1: VictimBW,LclNTWr,RmtNTWr > domain 1: > counter 0: LclFill,RmtFill,LclSlowFill,RmtSlowFill > counter 1: VictimBW,LclNTWr,RmtNTWr > group 1: > domain 0: > counter 2: LclFill,RmtFill,LclSlowFill,RmtSlowFill > counter 3: VictimBW,LclNTWr,RmtNTWr > domain 1: > counter 2: LclFill,RmtFill,LclSlowFill,RmtSlowFill > counter 3: VictimBW,LclNTWr,RmtNTWr > > You mention that you do not want counters to be allocated in domains that they > are not needed in. So, let's say group 0 does not need counter 0 and counter 1 > in domain 1, resulting in: > > group 0: > domain 0: > counter 0: LclFill,RmtFill,LclSlowFill,RmtSlowFill > counter 1: VictimBW,LclNTWr,RmtNTWr > group 1: > domain 0: > counter 2: LclFill,RmtFill,LclSlowFill,RmtSlowFill > counter 3: VictimBW,LclNTWr,RmtNTWr > domain 1: > counter 2: LclFill,RmtFill,LclSlowFill,RmtSlowFill > counter 3: VictimBW,LclNTWr,RmtNTWr > > With counter 0 and counter 1 available in domain 1, these counters could > theoretically be configured to give group 1 more data in domain 1: > > group 0: > domain 0: > counter 0: LclFill,RmtFill,LclSlowFill,RmtSlowFill > counter 1: VictimBW,LclNTWr,RmtNTWr > group 1: > domain 0: > counter 2: LclFill,RmtFill,LclSlowFill,RmtSlowFill > counter 3: VictimBW,LclNTWr,RmtNTWr > domain 1: > counter 0: LclFill,RmtFill > counter 1: LclNTWr,RmtNTWr > counter 2: LclSlowFill,RmtSlowFill > counter 3: VictimBW > > The counters are shown with different per-domain configurations that seems to > match with earlier goals of (a) choose events counted by each counter and > (b) do not allocate counters in domains where they are not needed. As I > understand the above does contradict global counter configuration though. > Or do you mean that only the *name* of the counter is global and then > that it is reconfigured as part of every assignment? Yes, I meant only the *name* is global. I assume based on a particular system configuration, the user will settle on a handful of useful groupings to count. Perhaps mbm_assign_control syntax is the clearest way to express an example... # define global configurations (in ABMC terms), not necessarily in this # syntax and probably not in the mbm_assign_control file. r=LclFill,RmtFill,LclSlowFill,RmtSlowFill w=VictimBW,LclNTWr,RmtNTWr # legacy "total" configuration, effectively r+w t=LclFill,RmtFill,LclSlowFill,RmtSlowFill,VictimBW,LclNTWr,RmtNTWr /group0/0=t;1=t /group1/0=t;1=t /group2/0=_;1=t /group3/0=rw;1=_ - group2 is restricted to domain 0 - group3 is restricted to domain 1 - the rest are unrestricted - In group3, we decided we need to separate read and write traffic This consumes 4 counters in domain 0 and 3 counters in domain 1. > > >> Until now I viewed counter configuration separate from counter assignment, > >> similar to how AMD's counters can be configured via mbm_total_bytes_config and > >> mbm_local_bytes_config before they are assigned. That is still per-domain > >> counter configuration though, not per-counter. > >> > >>> I assume packing all of this info for a group's desired counter > >>> configuration into a single line (with 32 domains per line on many > >>> dual-socket AMD configurations I see) would be difficult to look at, > >>> even if we could settle on a single letter to represent each > >>> universally. > >>> > >>>> > >>>> My goal is for resctrl to have a user interface that can as much as possible > >>>> be ready for whatever may be required from it years down the line. Of course, > >>>> I may be wrong and resctrl would never need to support more than 26 events per > >>>> resource (*). The risk is that resctrl *may* need to support more than 26 events > >>>> and how could resctrl support that? > >>>> > >>>> What is the risk of supporting more than 26 events? As I highlighted earlier > >>>> the interface I used as demonstration may become unwieldy to parse on a system > >>>> with many domains that supports many events. This is a concern for me. Any suggestions > >>>> will be appreciated, especially from you since I know that you are very familiar with > >>>> issues related to large scale use of resctrl interfaces. > >>> > >>> It's mainly just the unwieldiness of all the information in one file. > >>> It's already at the limit of what I can visually look through. > >> > >> I agree. > >> > >>> > >>> I believe that shared assignments will take care of all the > >>> high-frequency and performance-intensive batch configuration updates I > >>> was originally concerned about, so I no longer see much benefit in > >>> finding ways to textually encode all this information in a single file > >>> when it would be more manageable to distribute it around the > >>> filesystem hierarchy. > >> > >> This is significant. The motivation for the single file was to support > >> the "high-frequency and performance-intensive" usage. Would "shared assignments" > >> not also depend on the same files that, if distributed, will require many > >> filesystem operations? > >> Having the files distributed will be significantly simpler while also > >> avoiding the file size issue that Dave Martin exposed. > > > > The remaining filesystem operations will be assigning or removing > > shared counter assignments in the applicable domains, which would > > normally correspond to mkdir/rmdir of groups or changing their CPU > > affinity. The shared assignments are more "program and forget", while > > the exclusive assignment approach requires updates for every counter > > (in every domain) every few seconds to cover a large number of groups. > > > > When they want to pay extra attention to a particular group, I expect > > they'll ask for exclusive counters and leave them assigned for a while > > as they collect extra data. > > The single file approach is already unwieldy. The demands that will be > placed on it to support the usages currently being discussed would make this > interface even harder to use and manage. If the single file is not required > then I think we should go back to smaller files distributed in resctrl. > This may not even be an either/or argument. One way to view mbm_assign_control > could be as a way for user to interact with the distributed counter > related files with a single file system operation. Although, without > knowing how counter configuration is expected to work this remains unclear. If we do both interfaces and the multi-file model gives us more capability to express configurations, we could find situations where there are configurations we cannot represent when reading back from mbm_assign_control, or updates through mbm_assign_control have ambiguous effects on existing configurations which were created with other files. However, the example I gave above seems to be adequately represented by a minor extension to mbm_assign_control and we all seem to understand it now, so maybe it's not broken yet. It's unfortunate that work went into a requirement that's no longer relevant, but I don't think that on its own is a blocker. -Peter
