Re: [PATCH] x86/resctrl: avoid compiler optimization in __resctrl_sched_in

[Linus Torvalds]

On Tue, Mar 7, 2023 at 12:54 PM Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> I think the problem is that the <asm/resctrl.h> code is disgusting and
> horrible in multiple ways:
>
>  (a) it shouldn't define and declare a static function in a header file
>
>  (b) the resctrl_sched_in() inline function is misdesigned to begin with

Ok, so here's a *ttoally* untested and mindless patch to maybe fix
what I dislike about that resctl code.

Does it fix the code generation issue? I have no idea. But this is
what I would suggest is the right answer, without actually knowing the
code any better, and just going on a mindless rampage.

It seems to compile for me, fwiw.

             Linus
 arch/x86/include/asm/resctrl.h         | 12 ++++++------
 arch/x86/kernel/cpu/resctrl/rdtgroup.c |  4 ++--
 arch/x86/kernel/process_32.c           |  2 +-
 arch/x86/kernel/process_64.c           |  2 +-
 4 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
index 52788f79786f..255a78d9d906 100644
--- a/arch/x86/include/asm/resctrl.h
+++ b/arch/x86/include/asm/resctrl.h
@@ -49,7 +49,7 @@ DECLARE_STATIC_KEY_FALSE(rdt_mon_enable_key);
  *   simple as possible.
  * Must be called with preemption disabled.
  */
-static void __resctrl_sched_in(void)
+static inline void __resctrl_sched_in(struct task_struct *tsk)
 {
 	struct resctrl_pqr_state *state = this_cpu_ptr(&pqr_state);
 	u32 closid = state->default_closid;
@@ -61,13 +61,13 @@ static void __resctrl_sched_in(void)
 	 * Else use the closid/rmid assigned to this cpu.
 	 */
 	if (static_branch_likely(&rdt_alloc_enable_key)) {
-		tmp = READ_ONCE(current->closid);
+		tmp = READ_ONCE(tsk->closid);
 		if (tmp)
 			closid = tmp;
 	}
 
 	if (static_branch_likely(&rdt_mon_enable_key)) {
-		tmp = READ_ONCE(current->rmid);
+		tmp = READ_ONCE(tsk->rmid);
 		if (tmp)
 			rmid = tmp;
 	}
@@ -88,17 +88,17 @@ static inline unsigned int resctrl_arch_round_mon_val(unsigned int val)
 	return val * scale;
 }
 
-static inline void resctrl_sched_in(void)
+static inline void resctrl_sched_in(struct task_struct *tsk)
 {
 	if (static_branch_likely(&rdt_enable_key))
-		__resctrl_sched_in();
+		__resctrl_sched_in(tsk);
 }
 
 void resctrl_cpu_detect(struct cpuinfo_x86 *c);
 
 #else
 
-static inline void resctrl_sched_in(void) {}
+static inline void resctrl_sched_in(struct task_struct *tsk) {}
 static inline void resctrl_cpu_detect(struct cpuinfo_x86 *c) {}
 
 #endif /* CONFIG_X86_CPU_RESCTRL */
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index e2c1599d1b37..884b6e9a7e31 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -314,7 +314,7 @@ static void update_cpu_closid_rmid(void *info)
 	 * executing task might have its own closid selected. Just reuse
 	 * the context switch code.
 	 */
-	resctrl_sched_in();
+	resctrl_sched_in(current);
 }
 
 /*
@@ -530,7 +530,7 @@ static void _update_task_closid_rmid(void *task)
 	 * Otherwise, the MSR is updated when the task is scheduled in.
 	 */
 	if (task == current)
-		resctrl_sched_in();
+		resctrl_sched_in(task);
 }
 
 static void update_task_closid_rmid(struct task_struct *t)
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 470c128759ea..708c87b88cc1 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -212,7 +212,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 	switch_fpu_finish();
 
 	/* Load the Intel cache allocation PQR MSR. */
-	resctrl_sched_in();
+	resctrl_sched_in(next_p);
 
 	return prev_p;
 }
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 4e34b3b68ebd..bb65a68b4b49 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -656,7 +656,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 	}
 
 	/* Load the Intel cache allocation PQR MSR. */
-	resctrl_sched_in();
+	resctrl_sched_in(next_p);
 
 	return prev_p;
 }