Messages in this thread | | | Date | Tue, 16 Apr 2024 17:15:09 +0100 | From | Dave Martin <> | Subject | Re: [PATCH v1 02/31] x86/resctrl: Add a helper to avoid reaching into the arch code resource list |
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On Mon, Apr 15, 2024 at 03:28:18PM -0500, Moger, Babu wrote: > Hi James/Dave, > > On 3/21/24 11:50, James Morse wrote: > > Resctrl occasionally wants to know something about a specific resource, > > in these cases it reaches into the arch code's rdt_resources_all[] > > array. > > > > Once the filesystem parts of resctrl are moved to /fs/, this means it > > will need visibility of the architecture specific struct > > resctrl_hw_resource definition, and the array of all resources. > > All architectures would also need a r_resctrl member in this struct. > > > > Instead, abstract this via a helper to allow architectures to do > > different things here. Move the level enum to the resctrl header and > > add a helper to retrieve the struct rdt_resource by 'rid'. > > > > resctrl_arch_get_resource() should not return NULL for any value in > > the enum, it may instead return a dummy resource that is > > !alloc_enabled && !mon_enabled. > > Nit. > You may want to drop the second half of the statement. We don't have a > dummy resource.
I guess not, but MPAM will, although I haven't fully understood the logic. See:
https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git/tree/drivers/platform/mpam/mpam_resctrl.c?h=mpam/snapshot/v6.7-rc2
(Search for "dummy".)
In any case, the statement above is part of the definition of the new interface: the resctrl core code is going to explicitly need to cope with a dummy resource being returned, and the arch code is required to return a pointer to something and not NULL.
So I would say that it is appropriate (or, at the very least, harmless) to keep that statement here?
> > > > > Signed-off-by: James Morse <james.morse@arm.com> > > --- > > arch/x86/kernel/cpu/resctrl/core.c | 10 +++++++++- > > arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 2 +- > > arch/x86/kernel/cpu/resctrl/internal.h | 10 ---------- > > arch/x86/kernel/cpu/resctrl/monitor.c | 8 ++++---- > > arch/x86/kernel/cpu/resctrl/rdtgroup.c | 15 +++++++-------- > > include/linux/resctrl.h | 17 +++++++++++++++++ > > 6 files changed, 38 insertions(+), 24 deletions(-) > >
[...]
> > diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c > > index 1767c1affa60..45372b6a6215 100644 > > --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c > > +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
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> > @@ -2625,10 +2625,10 @@ static void schemata_list_destroy(void) > > > > static int rdt_get_tree(struct fs_context *fc) > > { > > + struct rdt_resource *l3 = resctrl_arch_get_resource(RDT_RESOURCE_L3); > > Its is probably best to keep the resource name as r here to be consistent > with other changes. > > > struct rdt_fs_context *ctx = rdt_fc2context(fc); > > unsigned long flags = RFTYPE_CTRL_BASE; > > struct rdt_domain *dom; > > - struct rdt_resource *r; > > int ret; > > > > cpus_read_lock(); > > @@ -2701,8 +2701,7 @@ static int rdt_get_tree(struct fs_context *fc) > > resctrl_mounted = true; > > > > if (is_mbm_enabled()) { > > - r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl; > > - list_for_each_entry(dom, &r->domains, list) > > + list_for_each_entry(dom, &l3->domains, list) > > mbm_setup_overflow_handler(dom, MBM_OVERFLOW_INTERVAL, > > RESCTRL_PICK_ANY_CPU); > > } > > @@ -3878,7 +3877,7 @@ static int rdtgroup_show_options(struct seq_file *seq, struct kernfs_root *kf)
[...]
> Thanks > Babu Moger
[...]
Yes, this does look a bit odd.
This looks like a no-op change to me -- I think that resctrl_arch_get_resource() is supposed to be without side-effects, so I would have expected this to be a one-line change at the assignment to r, with no particular need for renaming r.
Does that make sense to you, or is there some complexity I'm not noticing here?
Cheers ---Dave
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