diff mbox series

[07/18] x86/resctrl: Move CLOSID/RMID matching and setting to use helpers

Message ID 20221021131204.5581-8-james.morse@arm.com
State New
Headers
Series x86/resctrl: monitored closid+rmid together, separate arch/fs locking |

Commit Message

James Morse Oct. 21, 2022, 1:11 p.m. UTC 
  When switching tasks, the CLOSID and RMID that the new task should
use are stored in struct task_struct. For x86 the CLOSID known by resctrl,
the value in task_struct, and the value written to the CPU register are
all the same thing.

MPAM's CPU interface has two different PARTID's one for data accesses
the other for instruction fetch. Storing resctrl's CLOSID value in
struct task_struct implies the arch code knows whether resctrl is using
CDP.

Move the matching and setting of the struct task_struct properties
to use helpers. This allows arm64 to store the hardware format of
the register, instead of having to convert it each time.

__rdtgroup_move_task()s use of READ_ONCE()/WRITE_ONCE() ensures torn
values aren't seen as another CPU may schedule the task being moved
while the value is being changed. MPAM has an additional corner-case
here as the PMG bits extend the PARTID space. If the scheduler sees a
new-CLOSID but old-RMID, the task will dirty an RMID that the limbo code
is not watching causing an inaccurate count. x86's RMID are independent
values, so the limbo code will still be watching the old-RMID in this
circumstance.
To avoid this, arm64 needs both the CLOSID/RMID WRITE_ONCE()d together.
Both values must be provided together.

Because MPAM's RMID values are not unique, the CLOSID must be provided
when matching the RMID.

CC: Valentin Schneider <vschneid@redhat.com>
Signed-off-by: James Morse <james.morse@arm.com>
---
 arch/x86/include/asm/resctrl.h         | 18 ++++++++
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 57 +++++++++++++++-----------
 2 files changed, 51 insertions(+), 24 deletions(-)

Comments

Valentin Schneider Nov. 18, 2022, 3:49 p.m. UTC | #1 
On 21/10/22 13:11, James Morse wrote:
> When switching tasks, the CLOSID and RMID that the new task should
> use are stored in struct task_struct. For x86 the CLOSID known by resctrl,
> the value in task_struct, and the value written to the CPU register are
> all the same thing.
>
> MPAM's CPU interface has two different PARTID's one for data accesses
> the other for instruction fetch. Storing resctrl's CLOSID value in
> struct task_struct implies the arch code knows whether resctrl is using
> CDP.
>
> Move the matching and setting of the struct task_struct properties
> to use helpers. This allows arm64 to store the hardware format of
> the register, instead of having to convert it each time.
>
> __rdtgroup_move_task()s use of READ_ONCE()/WRITE_ONCE() ensures torn
> values aren't seen as another CPU may schedule the task being moved
> while the value is being changed. MPAM has an additional corner-case
> here as the PMG bits extend the PARTID space. If the scheduler sees a
> new-CLOSID but old-RMID, the task will dirty an RMID that the limbo code
> is not watching causing an inaccurate count. x86's RMID are independent
> values, so the limbo code will still be watching the old-RMID in this
> circumstance.
> To avoid this, arm64 needs both the CLOSID/RMID WRITE_ONCE()d together.
> Both values must be provided together.
>

I think I remember something about this... Is that about having them
union'd and read/written as one? (just for my own curiosity)

> Because MPAM's RMID values are not unique, the CLOSID must be provided
> when matching the RMID.
>
> CC: Valentin Schneider <vschneid@redhat.com>
> Signed-off-by: James Morse <james.morse@arm.com>

Reviewed-by: Valentin Schneider <vschneid@redhat.com>
James Morse Nov. 24, 2022, 2:21 p.m. UTC | #2 
Hi Valentin,

On 18/11/2022 15:49, Valentin Schneider wrote:
> On 21/10/22 13:11, James Morse wrote:
>> When switching tasks, the CLOSID and RMID that the new task should
>> use are stored in struct task_struct. For x86 the CLOSID known by resctrl,
>> the value in task_struct, and the value written to the CPU register are
>> all the same thing.
>>
>> MPAM's CPU interface has two different PARTID's one for data accesses
>> the other for instruction fetch. Storing resctrl's CLOSID value in
>> struct task_struct implies the arch code knows whether resctrl is using
>> CDP.
>>
>> Move the matching and setting of the struct task_struct properties
>> to use helpers. This allows arm64 to store the hardware format of
>> the register, instead of having to convert it each time.
>>
>> __rdtgroup_move_task()s use of READ_ONCE()/WRITE_ONCE() ensures torn
>> values aren't seen as another CPU may schedule the task being moved
>> while the value is being changed. MPAM has an additional corner-case
>> here as the PMG bits extend the PARTID space. If the scheduler sees a
>> new-CLOSID but old-RMID, the task will dirty an RMID that the limbo code
>> is not watching causing an inaccurate count. x86's RMID are independent
>> values, so the limbo code will still be watching the old-RMID in this
>> circumstance.
>> To avoid this, arm64 needs both the CLOSID/RMID WRITE_ONCE()d together.
>> Both values must be provided together.

> I think I remember something about this... Is that about having them
> union'd and read/written as one? (just for my own curiosity)

Yup. Many moons ago you pointed out that storing partid/pmg separately lets the remote
CPUs load torn values. arm64 not only needs the values as a pair, it needs to read/write
them as a pair.


>> Because MPAM's RMID values are not unique, the CLOSID must be provided
>> when matching the RMID.
>>
>> CC: Valentin Schneider <vschneid@redhat.com>

(CC here also stands for celebrate-contribution!)


>> Signed-off-by: James Morse <james.morse@arm.com>
> 
> Reviewed-by: Valentin Schneider <vschneid@redhat.com>

Thanks!

James
diff mbox series

Patch

diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
index 523eabfa3193..edf4368ea25e 100644
--- a/arch/x86/include/asm/resctrl.h
+++ b/arch/x86/include/asm/resctrl.h
@@ -90,6 +90,24 @@  static inline unsigned int resctrl_arch_round_mon_val(unsigned int val)
 	return val * scale;
 }
 
+static inline void resctrl_arch_set_closid_rmid(struct task_struct *tsk,
+						u32 closid, u32 rmid)
+{
+	WRITE_ONCE(tsk->closid, closid);
+	WRITE_ONCE(tsk->rmid, rmid);
+}
+
+static inline bool resctrl_arch_match_closid(struct task_struct *tsk, u32 closid)
+{
+	return READ_ONCE(tsk->closid) == closid;
+}
+
+static inline bool resctrl_arch_match_rmid(struct task_struct *tsk, u32 ignored,
+					   u32 rmid)
+{
+	return READ_ONCE(tsk->rmid) == rmid;
+}
+
 static inline void resctrl_sched_in(void)
 {
 	if (static_branch_likely(&rdt_enable_key))
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 59f33adcf6f8..0dd1b3391200 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -84,7 +84,7 @@  void rdt_last_cmd_printf(const char *fmt, ...)
  *
  * Using a global CLOSID across all resources has some advantages and
  * some drawbacks:
- * + We can simply set "current->closid" to assign a task to a resource
+ * + We can simply set current's closid to assign a task to a resource
  *   group.
  * + Context switch code can avoid extra memory references deciding which
  *   CLOSID to load into the PQR_ASSOC MSR
@@ -550,14 +550,26 @@  static void update_task_closid_rmid(struct task_struct *t)
 		_update_task_closid_rmid(t);
 }
 
+static bool task_in_rdtgroup(struct task_struct *tsk, struct rdtgroup *rdtgrp)
+{
+	u32 closid, rmid = rdtgrp->mon.rmid;
+
+	if (rdtgrp->type == RDTCTRL_GROUP)
+		closid = rdtgrp->closid;
+	else if (rdtgrp->type == RDTMON_GROUP)
+		closid = rdtgrp->mon.parent->closid;
+	else
+		return false;
+
+	return resctrl_arch_match_closid(tsk, closid) &&
+	       resctrl_arch_match_rmid(tsk, closid, rmid);
+}
+
 static int __rdtgroup_move_task(struct task_struct *tsk,
 				struct rdtgroup *rdtgrp)
 {
 	/* If the task is already in rdtgrp, no need to move the task. */
-	if ((rdtgrp->type == RDTCTRL_GROUP && tsk->closid == rdtgrp->closid &&
-	     tsk->rmid == rdtgrp->mon.rmid) ||
-	    (rdtgrp->type == RDTMON_GROUP && tsk->rmid == rdtgrp->mon.rmid &&
-	     tsk->closid == rdtgrp->mon.parent->closid))
+	if (task_in_rdtgroup(tsk, rdtgrp))
 		return 0;
 
 	/*
@@ -568,19 +580,14 @@  static int __rdtgroup_move_task(struct task_struct *tsk,
 	 * For monitor groups, can move the tasks only from
 	 * their parent CTRL group.
 	 */
-
-	if (rdtgrp->type == RDTCTRL_GROUP) {
-		WRITE_ONCE(tsk->closid, rdtgrp->closid);
-		WRITE_ONCE(tsk->rmid, rdtgrp->mon.rmid);
-	} else if (rdtgrp->type == RDTMON_GROUP) {
-		if (rdtgrp->mon.parent->closid == tsk->closid) {
-			WRITE_ONCE(tsk->rmid, rdtgrp->mon.rmid);
-		} else {
-			rdt_last_cmd_puts("Can't move task to different control group\n");
-			return -EINVAL;
-		}
+	if (rdtgrp->type == RDTMON_GROUP &&
+	    !resctrl_arch_match_closid(tsk, rdtgrp->mon.parent->closid)) {
+		rdt_last_cmd_puts("Can't move task to different control group\n");
+		return -EINVAL;
 	}
 
+	resctrl_arch_set_closid_rmid(tsk, rdtgrp->closid, rdtgrp->mon.rmid);
+
 	/*
 	 * Ensure the task's closid and rmid are written before determining if
 	 * the task is current that will decide if it will be interrupted.
@@ -600,14 +607,15 @@  static int __rdtgroup_move_task(struct task_struct *tsk,
 
 static bool is_closid_match(struct task_struct *t, struct rdtgroup *r)
 {
-	return (rdt_alloc_capable &&
-	       (r->type == RDTCTRL_GROUP) && (t->closid == r->closid));
+	return (rdt_alloc_capable && (r->type == RDTCTRL_GROUP) &&
+		resctrl_arch_match_closid(t, r->closid));
 }
 
 static bool is_rmid_match(struct task_struct *t, struct rdtgroup *r)
 {
-	return (rdt_mon_capable &&
-	       (r->type == RDTMON_GROUP) && (t->rmid == r->mon.rmid));
+	return (rdt_mon_capable && (r->type == RDTMON_GROUP) &&
+		resctrl_arch_match_rmid(t, r->mon.parent->closid,
+					r->mon.rmid));
 }
 
 /**
@@ -803,7 +811,7 @@  int proc_resctrl_show(struct seq_file *s, struct pid_namespace *ns,
 		    rdtg->mode != RDT_MODE_EXCLUSIVE)
 			continue;
 
-		if (rdtg->closid != tsk->closid)
+		if (!resctrl_arch_match_closid(tsk, rdtg->closid))
 			continue;
 
 		seq_printf(s, "res:%s%s\n", (rdtg == &rdtgroup_default) ? "/" : "",
@@ -811,7 +819,8 @@  int proc_resctrl_show(struct seq_file *s, struct pid_namespace *ns,
 		seq_puts(s, "mon:");
 		list_for_each_entry(crg, &rdtg->mon.crdtgrp_list,
 				    mon.crdtgrp_list) {
-			if (tsk->rmid != crg->mon.rmid)
+			if (!resctrl_arch_match_rmid(tsk, crg->mon.parent->closid,
+						     crg->mon.rmid))
 				continue;
 			seq_printf(s, "%s", crg->kn->name);
 			break;
@@ -2402,8 +2411,8 @@  static void rdt_move_group_tasks(struct rdtgroup *from, struct rdtgroup *to,
 	for_each_process_thread(p, t) {
 		if (!from || is_closid_match(t, from) ||
 		    is_rmid_match(t, from)) {
-			WRITE_ONCE(t->closid, to->closid);
-			WRITE_ONCE(t->rmid, to->mon.rmid);
+			resctrl_arch_set_closid_rmid(t, to->closid,
+						     to->mon.rmid);
 
 			/*
 			 * If the task is on a CPU, set the CPU in the mask.