Messages in this thread | | | Date | Wed, 17 Apr 2024 15:40:53 +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 Tue, Apr 16, 2024 at 03:44:29PM -0500, Moger, Babu wrote: > Hi Dave, > > On 4/16/24 11:15, Dave Martin wrote: > > 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? > > Ok. fine. > > > >> > >>> > >>> 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 > > > > [...] > > > >>> @@ -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? > > No other complexity.. Just keep the variable name as r. > > struct rdt_resource *r = resctrl_arch_get_resource(RDT_RESOURCE_L3);
Ack; I went for the minimum-diffstat option in the end, so kept the declaration and initialiser separate. If you have a strong view on that though, please shout.
Cheers ---Dave
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