Hi Peter, On Mon, Apr 22, 2024 at 11:23:50AM -0700, Peter Newman wrote: > Hi Dave, > > On Mon, Apr 22, 2024 at 9:33 AM Dave Martin <Dave.Martin@xxxxxxx> wrote: > > > > Hi Babu, > > > > On Thu, Mar 28, 2024 at 08:06:33PM -0500, Babu Moger wrote: > > > Assignment flags can be one of the following: > > > > > > t MBM total event is assigned > > > > With my MPAM hat on this looks a bit weird, although I suppose it > > follows on from the way "mbm_total_bytes" and "mbm_local_bytes" are > > already exposed in resctrlfs. > > > > From an abstract point of view, "total" and "local" are just event > > selection criteria, additional to those in mbm_cfg_mask. The different > > way they are treated in the hardware feels like an x86 implementation > > detail. > > > > For MPAM we don't currently distinguish local from non-local traffic, so > > I guess this just reduces to a simple on-off (i.e., "t" or nothing), > > which I guess is tolerable. > > > > This might want more thought if there is an expectation that more > > categories will be added here, though (?) > > There should be a path forward whenever we start supporting > user-configured counter classes. I assume the letters a-z will be > enough to cover all the counter classes which could be used at once. Ack, though I'd appreciate a response on the point about "_" below in case people missed it. > > > > > > l MBM local event is assigned > > > tl Both total and local MBM events are assigned > > > _ None of the MBM events are assigned > > > > This use of '_' seems unusual. Can we not just have the empty string > > for "nothing assigned"? > > > > Since every assignment is terminated by ';' or end-of-line, I don't > > think that there would be any parsing ambiguity (?) > > > > > > > > Examples: > > > > > > # cat /sys/fs/resctrl/info/L3_MON/mbm_assign_control > > > non_defult_group//0=tl;1=tl;2=tl;3=tl;4=tl;5=tl;6=tl;7=tl; > > > non_defult_group/non_default_mon1/0=tl;1=tl;2=tl;3=tl;4=tl;5=tl;6=tl;7=tl; > > > //0=tl;1=tl;2=tl;3=tl;4=tl;5=tl;6=tl;7=tl; > > > /default_mon1/0=tl;1=tl;2=tl;3=tl;4=tl;5=tl;6=tl;7=tl; > > > > > > There are four groups and all the groups have local and total event assigned. > > > > > > "//" - This is a default CONTROL MON group > > > > > > "non_defult_group//" - This is non default CONTROL MON group > > > > > > "/default_mon1/" - This is Child MON group of the defult group > > > > > > "non_defult_group/non_default_mon1/" - This is child MON group of the non default group > > > > > > =tl means both total and local events are assigned. > > > > > > e. Update the group assignment states using the interface file /sys/fs/resctrl/info/L3_MON/mbm_assign_control. > > > > > > The write format is similar to the above list format with addition of > > > op-code for the assignment operation. > > > > With by resctrl newbie hat on: > > > > It feels a bit complex (for the kernel) to have userspace needing to > > write a script into a magic file that we need to parse, specifying > > updates to a bunch of controls already visible as objects in resctrlfs > > in their own right. > > > > What's the expected use case here? > > I went over the use case of iterating a small number of monitors over > a much larger number of monitoring groups here: > > https://lore.kernel.org/lkml/CALPaoCi=PCWr6U5zYtFPmyaFHU_iqZtZL-LaHC2mYxbETXk3ig@xxxxxxxxxxxxxx/ > > > > > If userspace really does need to switch lots of events simultaneously > > then I guess the overhead of enumerating and poking lots of individual > > files might be unacceptable though, and we would still need some global > > interfaces for operations such as "unassign everything"... > > My main goal is for the number of parallel IPI batches to all the > domains (or write syscalls) to be O(num_rmids / num_monitors) rather > than O(num_rmids * num_monitors) as I need to know how frequently we > can afford to sample the current memory bandwidth of the maximum > number of monitoring groups supported. Fair enough; I wasn't fully aware of the background discussions. Cheers ---Dave
