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Date:   Tue, 26 Sep 2023 11:46:32 -0700
From:   Tony Luck <tony.luck@intel.com>
To:     Reinette Chatre <reinette.chatre@intel.com>
Cc:     Fenghua Yu <fenghua.yu@intel.com>,
        Peter Newman <peternewman@google.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Shuah Khan <skhan@linuxfoundation.org>, x86@kernel.org,
        Shaopeng Tan <tan.shaopeng@fujitsu.com>,
        James Morse <james.morse@arm.com>,
        Jamie Iles <quic_jiles@quicinc.com>,
        Babu Moger <babu.moger@amd.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        patches@lists.linux.dev
Subject: Re: [PATCH v5 3/8] x86/resctrl: Split the rdt_domain structure
Message-ID: <ZRMnCFWzcxa6Qa4E@agluck-desk3>
References: <20230722190740.326190-1-tony.luck@intel.com>
 <20230829234426.64421-1-tony.luck@intel.com>
 <20230829234426.64421-4-tony.luck@intel.com>
 <5f1256d3-737e-a447-abbe-f541767b2c8f@intel.com>
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In-Reply-To: <5f1256d3-737e-a447-abbe-f541767b2c8f@intel.com>
Precedence: bulk

On Mon, Sep 25, 2023 at 04:25:15PM -0700, Reinette Chatre wrote:
> > +struct rdt_domain {
> > +	// First three fields must match struct rdt_mondomain below.
> 
> Please avoid comments within declarations. Even so, could you please
> elaborate what the above means? Why do the first three fields have to
> match? I understand there is common code, for example, __rdt_find_domain()
> that operated on the same members of the two structs but does that
> require the members be in the same position in the struct?
> I understand that a comment may be required if position in the struct
> is important but I cannot see that it is.

[Just replying to this one point in your message to get guidance. I'll
address all the rest in other replies]

I'm wrong about the first *three* fields ... but the first *two* fields
(the "list" and the "id") do need to be at the same offsets in different
structures if a common routine is going to be used to access those
fields.

If the "id" were at offset 0x10 in the control version of the domain
structure, and at offset 0x20 in the monitor version of the domain
structure, there would be no hope for a common routine to access the
"id" field when searching a list that could be either control or
monitor domains.

I'm looking at making this far more explicit with a new patch between
0001 and 0002 that pulls the two fields into a common substructure that
will be included in each of the control and monitor versions of the
structure.

Patch included below.

But this seems like it is a lot of churn to avoid having separate
functions to search control and monitor lists. Each a clone of
the existing ~24 line rdt_find_domain() with just the type changed
for the return value and the list travsersal.

What do you think?

-Tony

commit 08992b4be1f53a3144f8aadd821f815a40a05e75
Author: Tony Luck <tony.luck@intel.com>
Date:   Tue Sep 26 11:07:12 2023 -0700

    x86/resctrl: Prepare to split rdt_domain structure
    
    The rdt_domain structure is used for both control and monitor features.
    It is about to be split into separate structures for these two usages
    because the scope for control and monitoring features for a resource
    will be different for future resources.
    
    To allow for common code that scans a list of domains looking for a
    specific domain id, move the "list" and "id" fields into their own
    structure within the rdt_domain structure.
    
    Signed-off-by: Tony Luck <tony.luck@intel.com>

diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index 618735e396cb..a583fa88ea5a 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -53,9 +53,18 @@ struct resctrl_staged_config {
 };
 
 /**
- * struct rdt_domain - group of CPUs sharing a resctrl resource
+ * struct rdt_domain_hdr - common header for different domain types
  * @list:		all instances of this resource
  * @id:			unique id for this instance
+ */
+struct rdt_domain_hdr {
+	struct list_head		list;
+	int				id;
+};
+
+/**
+ * struct rdt_domain - group of CPUs sharing a resctrl resource
+ * @hdr:		common header for different domain types
  * @cpu_mask:		which CPUs share this resource
  * @rmid_busy_llc:	bitmap of which limbo RMIDs are above threshold
  * @mbm_total:		saved state for MBM total bandwidth
@@ -71,8 +80,7 @@ struct resctrl_staged_config {
  *			by closid
  */
 struct rdt_domain {
-	struct list_head		list;
-	int				id;
+	struct rdt_domain_hdr		hdr;
 	struct cpumask			cpu_mask;
 	unsigned long			*rmid_busy_llc;
 	struct mbm_state		*mbm_total;
diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index 3b1837e1fb6b..05369add4578 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -352,7 +352,7 @@ struct rdt_domain *get_domain_from_cpu(int cpu, struct rdt_resource *r)
 {
 	struct rdt_domain *d;
 
-	list_for_each_entry(d, &r->domains, list) {
+	list_for_each_entry(d, &r->domains, hdr.list) {
 		/* Find the domain that contains this CPU */
 		if (cpumask_test_cpu(cpu, &d->cpu_mask))
 			return d;
@@ -401,12 +401,12 @@ struct rdt_domain *rdt_find_domain(struct rdt_resource *r, int id,
 		return ERR_PTR(-ENODEV);
 
 	list_for_each(l, &r->domains) {
-		d = list_entry(l, struct rdt_domain, list);
+		d = list_entry(l, struct rdt_domain, hdr.list);
 		/* When id is found, return its domain. */
-		if (id == d->id)
+		if (id == d->hdr.id)
 			return d;
 		/* Stop searching when finding id's position in sorted list. */
-		if (id < d->id)
+		if (id < d->hdr.id)
 			break;
 	}
 
@@ -544,7 +544,7 @@ static void domain_add_cpu(int cpu, struct rdt_resource *r)
 		return;
 
 	d = &hw_dom->d_resctrl;
-	d->id = id;
+	d->hdr.id = id;
 	cpumask_set_cpu(cpu, &d->cpu_mask);
 
 	rdt_domain_reconfigure_cdp(r);
@@ -559,11 +559,11 @@ static void domain_add_cpu(int cpu, struct rdt_resource *r)
 		return;
 	}
 
-	list_add_tail(&d->list, add_pos);
+	list_add_tail(&d->hdr.list, add_pos);
 
 	err = resctrl_online_domain(r, d);
 	if (err) {
-		list_del(&d->list);
+		list_del(&d->hdr.list);
 		domain_free(hw_dom);
 	}
 }
@@ -587,7 +587,7 @@ static void domain_remove_cpu(int cpu, struct rdt_resource *r)
 	cpumask_clear_cpu(cpu, &d->cpu_mask);
 	if (cpumask_empty(&d->cpu_mask)) {
 		resctrl_offline_domain(r, d);
-		list_del(&d->list);
+		list_del(&d->hdr.list);
 
 		/*
 		 * rdt_domain "d" is going to be freed below, so clear
diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
index b44c487727d4..8bce591a1018 100644
--- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
+++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
@@ -67,7 +67,7 @@ int parse_bw(struct rdt_parse_data *data, struct resctrl_schema *s,
 
 	cfg = &d->staged_config[s->conf_type];
 	if (cfg->have_new_ctrl) {
-		rdt_last_cmd_printf("Duplicate domain %d\n", d->id);
+		rdt_last_cmd_printf("Duplicate domain %d\n", d->hdr.id);
 		return -EINVAL;
 	}
 
@@ -144,7 +144,7 @@ int parse_cbm(struct rdt_parse_data *data, struct resctrl_schema *s,
 
 	cfg = &d->staged_config[s->conf_type];
 	if (cfg->have_new_ctrl) {
-		rdt_last_cmd_printf("Duplicate domain %d\n", d->id);
+		rdt_last_cmd_printf("Duplicate domain %d\n", d->hdr.id);
 		return -EINVAL;
 	}
 
@@ -224,8 +224,8 @@ static int parse_line(char *line, struct resctrl_schema *s,
 		return -EINVAL;
 	}
 	dom = strim(dom);
-	list_for_each_entry(d, &r->domains, list) {
-		if (d->id == dom_id) {
+	list_for_each_entry(d, &r->domains, hdr.list) {
+		if (d->hdr.id == dom_id) {
 			data.buf = dom;
 			data.rdtgrp = rdtgrp;
 			if (r->parse_ctrlval(&data, s, d))
@@ -316,7 +316,7 @@ int resctrl_arch_update_domains(struct rdt_resource *r, u32 closid)
 		return -ENOMEM;
 
 	msr_param.res = NULL;
-	list_for_each_entry(d, &r->domains, list) {
+	list_for_each_entry(d, &r->domains, hdr.list) {
 		hw_dom = resctrl_to_arch_dom(d);
 		for (t = 0; t < CDP_NUM_TYPES; t++) {
 			cfg = &hw_dom->d_resctrl.staged_config[t];
@@ -464,7 +464,7 @@ static void show_doms(struct seq_file *s, struct resctrl_schema *schema, int clo
 	u32 ctrl_val;
 
 	seq_printf(s, "%*s:", max_name_width, schema->name);
-	list_for_each_entry(dom, &r->domains, list) {
+	list_for_each_entry(dom, &r->domains, hdr.list) {
 		if (sep)
 			seq_puts(s, ";");
 
@@ -474,7 +474,7 @@ static void show_doms(struct seq_file *s, struct resctrl_schema *schema, int clo
 			ctrl_val = resctrl_arch_get_config(r, dom, closid,
 							   schema->conf_type);
 
-		seq_printf(s, r->format_str, dom->id, max_data_width,
+		seq_printf(s, r->format_str, dom->hdr.id, max_data_width,
 			   ctrl_val);
 		sep = true;
 	}
@@ -503,7 +503,7 @@ int rdtgroup_schemata_show(struct kernfs_open_file *of,
 			} else {
 				seq_printf(s, "%s:%d=%x\n",
 					   rdtgrp->plr->s->res->name,
-					   rdtgrp->plr->d->id,
+					   rdtgrp->plr->d->hdr.id,
 					   rdtgrp->plr->cbm);
 			}
 		} else {
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index ded1fc7cb7cb..27cda5988d7f 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -340,7 +340,7 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
 
 	entry->busy = 0;
 	cpu = get_cpu();
-	list_for_each_entry(d, &r->domains, list) {
+	list_for_each_entry(d, &r->domains, hdr.list) {
 		if (cpumask_test_cpu(cpu, &d->cpu_mask)) {
 			err = resctrl_arch_rmid_read(r, d, entry->rmid,
 						     QOS_L3_OCCUP_EVENT_ID,
diff --git a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
index 8c5f932bc00b..18b6183a1b48 100644
--- a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
+++ b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
@@ -856,7 +856,7 @@ bool rdtgroup_pseudo_locked_in_hierarchy(struct rdt_domain *d)
 	 * associated with them.
 	 */
 	for_each_alloc_capable_rdt_resource(r) {
-		list_for_each_entry(d_i, &r->domains, list) {
+		list_for_each_entry(d_i, &r->domains, hdr.list) {
 			if (d_i->plr)
 				cpumask_or(cpu_with_psl, cpu_with_psl,
 					   &d_i->cpu_mask);
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 1cf2b36f5bf8..42adf17ea6fa 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -86,7 +86,7 @@ void rdt_staged_configs_clear(void)
 	lockdep_assert_held(&rdtgroup_mutex);
 
 	for_each_alloc_capable_rdt_resource(r) {
-		list_for_each_entry(dom, &r->domains, list)
+		list_for_each_entry(dom, &r->domains, hdr.list)
 			memset(dom->staged_config, 0, sizeof(dom->staged_config));
 	}
 }
@@ -928,12 +928,12 @@ static int rdt_bit_usage_show(struct kernfs_open_file *of,
 
 	mutex_lock(&rdtgroup_mutex);
 	hw_shareable = r->cache.shareable_bits;
-	list_for_each_entry(dom, &r->domains, list) {
+	list_for_each_entry(dom, &r->domains, hdr.list) {
 		if (sep)
 			seq_putc(seq, ';');
 		sw_shareable = 0;
 		exclusive = 0;
-		seq_printf(seq, "%d=", dom->id);
+		seq_printf(seq, "%d=", dom->hdr.id);
 		for (i = 0; i < closids_supported(); i++) {
 			if (!closid_allocated(i))
 				continue;
@@ -1233,7 +1233,7 @@ static bool rdtgroup_mode_test_exclusive(struct rdtgroup *rdtgrp)
 		if (r->rid == RDT_RESOURCE_MBA || r->rid == RDT_RESOURCE_SMBA)
 			continue;
 		has_cache = true;
-		list_for_each_entry(d, &r->domains, list) {
+		list_for_each_entry(d, &r->domains, hdr.list) {
 			ctrl = resctrl_arch_get_config(r, d, closid,
 						       s->conf_type);
 			if (rdtgroup_cbm_overlaps(s, d, ctrl, closid, false)) {
@@ -1398,7 +1398,7 @@ static int rdtgroup_size_show(struct kernfs_open_file *of,
 			size = rdtgroup_cbm_to_size(rdtgrp->plr->s->res,
 						    rdtgrp->plr->d,
 						    rdtgrp->plr->cbm);
-			seq_printf(s, "%d=%u\n", rdtgrp->plr->d->id, size);
+			seq_printf(s, "%d=%u\n", rdtgrp->plr->d->hdr.id, size);
 		}
 		goto out;
 	}
@@ -1410,7 +1410,7 @@ static int rdtgroup_size_show(struct kernfs_open_file *of,
 		type = schema->conf_type;
 		sep = false;
 		seq_printf(s, "%*s:", max_name_width, schema->name);
-		list_for_each_entry(d, &r->domains, list) {
+		list_for_each_entry(d, &r->domains, hdr.list) {
 			if (sep)
 				seq_putc(s, ';');
 			if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKSETUP) {
@@ -1428,7 +1428,7 @@ static int rdtgroup_size_show(struct kernfs_open_file *of,
 				else
 					size = rdtgroup_cbm_to_size(r, d, ctrl);
 			}
-			seq_printf(s, "%d=%u", d->id, size);
+			seq_printf(s, "%d=%u", d->hdr.id, size);
 			sep = true;
 		}
 		seq_putc(s, '\n');
@@ -1499,7 +1499,7 @@ static int mbm_config_show(struct seq_file *s, struct rdt_resource *r, u32 evtid
 
 	mutex_lock(&rdtgroup_mutex);
 
-	list_for_each_entry(dom, &r->domains, list) {
+	list_for_each_entry(dom, &r->domains, hdr.list) {
 		if (sep)
 			seq_puts(s, ";");
 
@@ -1507,7 +1507,7 @@ static int mbm_config_show(struct seq_file *s, struct rdt_resource *r, u32 evtid
 		mon_info.evtid = evtid;
 		mondata_config_read(dom, &mon_info);
 
-		seq_printf(s, "%d=0x%02x", dom->id, mon_info.mon_config);
+		seq_printf(s, "%d=0x%02x", dom->hdr.id, mon_info.mon_config);
 		sep = true;
 	}
 	seq_puts(s, "\n");
@@ -1622,8 +1622,8 @@ static int mon_config_write(struct rdt_resource *r, char *tok, u32 evtid)
 		return -EINVAL;
 	}
 
-	list_for_each_entry(d, &r->domains, list) {
-		if (d->id == dom_id) {
+	list_for_each_entry(d, &r->domains, hdr.list) {
+		if (d->hdr.id == dom_id) {
 			ret = mbm_config_write_domain(r, d, evtid, val);
 			if (ret)
 				return -EINVAL;
@@ -2141,7 +2141,7 @@ static int set_cache_qos_cfg(int level, bool enable)
 		return -ENOMEM;
 
 	r_l = &rdt_resources_all[level].r_resctrl;
-	list_for_each_entry(d, &r_l->domains, list) {
+	list_for_each_entry(d, &r_l->domains, hdr.list) {
 		if (r_l->cache.arch_has_per_cpu_cfg)
 			/* Pick all the CPUs in the domain instance */
 			for_each_cpu(cpu, &d->cpu_mask)
@@ -2226,7 +2226,7 @@ static int set_mba_sc(bool mba_sc)
 
 	r->membw.mba_sc = mba_sc;
 
-	list_for_each_entry(d, &r->domains, list) {
+	list_for_each_entry(d, &r->domains, hdr.list) {
 		for (i = 0; i < num_closid; i++)
 			d->mbps_val[i] = MBA_MAX_MBPS;
 	}
@@ -2528,7 +2528,7 @@ static int rdt_get_tree(struct fs_context *fc)
 
 	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, &r->domains, hdr.list)
 			mbm_setup_overflow_handler(dom, MBM_OVERFLOW_INTERVAL);
 	}
 
@@ -2652,7 +2652,7 @@ static int reset_all_ctrls(struct rdt_resource *r)
 	 * CBMs in all domains to the maximum mask value. Pick one CPU
 	 * from each domain to update the MSRs below.
 	 */
-	list_for_each_entry(d, &r->domains, list) {
+	list_for_each_entry(d, &r->domains, hdr.list) {
 		hw_dom = resctrl_to_arch_dom(d);
 		cpumask_set_cpu(cpumask_any(&d->cpu_mask), cpu_mask);
 
@@ -2858,7 +2858,7 @@ static int mkdir_mondata_subdir(struct kernfs_node *parent_kn,
 	char name[32];
 	int ret;
 
-	sprintf(name, "mon_%s_%02d", r->name, d->id);
+	sprintf(name, "mon_%s_%02d", r->name, d->hdr.id);
 	/* create the directory */
 	kn = kernfs_create_dir(parent_kn, name, parent_kn->mode, prgrp);
 	if (IS_ERR(kn))
@@ -2874,7 +2874,7 @@ static int mkdir_mondata_subdir(struct kernfs_node *parent_kn,
 	}
 
 	priv.u.rid = r->rid;
-	priv.u.domid = d->id;
+	priv.u.domid = d->hdr.id;
 	list_for_each_entry(mevt, &r->evt_list, list) {
 		priv.u.evtid = mevt->evtid;
 		ret = mon_addfile(kn, mevt->name, priv.priv);
@@ -2922,7 +2922,7 @@ static int mkdir_mondata_subdir_alldom(struct kernfs_node *parent_kn,
 	struct rdt_domain *dom;
 	int ret;
 
-	list_for_each_entry(dom, &r->domains, list) {
+	list_for_each_entry(dom, &r->domains, hdr.list) {
 		ret = mkdir_mondata_subdir(parent_kn, dom, r, prgrp);
 		if (ret)
 			return ret;
@@ -3081,7 +3081,7 @@ static int __init_one_rdt_domain(struct rdt_domain *d, struct resctrl_schema *s,
 	 */
 	tmp_cbm = cfg->new_ctrl;
 	if (bitmap_weight(&tmp_cbm, r->cache.cbm_len) < r->cache.min_cbm_bits) {
-		rdt_last_cmd_printf("No space on %s:%d\n", s->name, d->id);
+		rdt_last_cmd_printf("No space on %s:%d\n", s->name, d->hdr.id);
 		return -ENOSPC;
 	}
 	cfg->have_new_ctrl = true;
@@ -3104,7 +3104,7 @@ static int rdtgroup_init_cat(struct resctrl_schema *s, u32 closid)
 	struct rdt_domain *d;
 	int ret;
 
-	list_for_each_entry(d, &s->res->domains, list) {
+	list_for_each_entry(d, &s->res->domains, hdr.list) {
 		ret = __init_one_rdt_domain(d, s, closid);
 		if (ret < 0)
 			return ret;
@@ -3119,7 +3119,7 @@ static void rdtgroup_init_mba(struct rdt_resource *r, u32 closid)
 	struct resctrl_staged_config *cfg;
 	struct rdt_domain *d;
 
-	list_for_each_entry(d, &r->domains, list) {
+	list_for_each_entry(d, &r->domains, hdr.list) {
 		if (is_mba_sc(r)) {
 			d->mbps_val[closid] = MBA_MAX_MBPS;
 			continue;
@@ -3726,7 +3726,7 @@ void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d)
 	 * per domain monitor data directories.
 	 */
 	if (static_branch_unlikely(&rdt_mon_enable_key))
-		rmdir_mondata_subdir_allrdtgrp(r, d->id);
+		rmdir_mondata_subdir_allrdtgrp(r, d->hdr.id);
 
 	if (is_mbm_enabled())
 		cancel_delayed_work(&d->mbm_over);