linux-kernel - [RFC PATCH 08/14] powerpc/thread_info: Introduce TIF_NOTIFY

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Date: Tue, 20 Feb 2024 22:44:51 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: <linux-kernel@...r.kernel.org>
CC: "Gautham R. Shenoy" <gautham.shenoy@....com>, K Prateek Nayak
	<kprateek.nayak@....com>, Michael Ellerman <mpe@...erman.id.au>, "Nicholas
 Piggin" <npiggin@...il.com>, Christophe Leroy <christophe.leroy@...roup.eu>,
	Aneesh Kumar K.V <aneesh.kumar@...nel.org>, "Naveen N. Rao"
	<naveen.n.rao@...ux.ibm.com>, "Rafael J. Wysocki" <rafael@...nel.org>,
	"Daniel Lezcano" <daniel.lezcano@...aro.org>, Ingo Molnar <mingo@...hat.com>,
	"Peter Zijlstra" <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>,
	"Vincent Guittot" <vincent.guittot@...aro.org>, Dietmar Eggemann
	<dietmar.eggemann@....com>, Steven Rostedt <rostedt@...dmis.org>, Ben Segall
	<bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, "Daniel Bristot de
 Oliveira" <bristot@...hat.com>, Valentin Schneider <vschneid@...hat.com>,
	Andrew Donnellan <ajd@...ux.ibm.com>, Nicholas Miehlbradt
	<nicholas@...ux.ibm.com>, <linuxppc-dev@...ts.ozlabs.org>,
	<linux-pm@...r.kernel.org>
Subject: [RFC PATCH 08/14] powerpc/thread_info: Introduce TIF_NOTIFY_IPI flag

Add support for TIF_NOTIFY_IPI on PowerPC. With TIF_NOTIFY_IPI, a sender
sending an IPI to an idle CPU in TIF_POLLING mode will set the
TIF_NOTIFY_IPI flag in the target's idle tasks's thread_info to pull the
CPU out of idle, as opposed to setting TIF_NEED_RESCHED previously. This
avoids spurious calls to schedule_idle() in cases where an IPI does not
necessarily wake up a task on the idle CPU.

Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: Nicholas Piggin <npiggin@...il.com>
Cc: Christophe Leroy <christophe.leroy@...roup.eu>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@...nel.org>
Cc: "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Juri Lelli <juri.lelli@...hat.com>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ben Segall <bsegall@...gle.com>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
Cc: Valentin Schneider <vschneid@...hat.com>
Cc: Andrew Donnellan <ajd@...ux.ibm.com>
Cc: K Prateek Nayak <kprateek.nayak@....com>
Cc: Nicholas Miehlbradt <nicholas@...ux.ibm.com>
Cc: linuxppc-dev@...ts.ozlabs.org
Cc: linux-kernel@...r.kernel.org
Cc: linux-pm@...r.kernel.org
Signed-off-by: K Prateek Nayak <kprateek.nayak@....com>
---
 arch/powerpc/include/asm/thread_info.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
index bf5dde1a4114..b48db55192e0 100644
--- a/arch/powerpc/include/asm/thread_info.h
+++ b/arch/powerpc/include/asm/thread_info.h
@@ -103,6 +103,7 @@ void arch_setup_new_exec(void);
 #define TIF_PATCH_PENDING	6	/* pending live patching update */
 #define TIF_SYSCALL_AUDIT	7	/* syscall auditing active */
 #define TIF_SINGLESTEP		8	/* singlestepping active */
+#define TIF_NOTIFY_IPI		9	/* Pending IPI on TIF_POLLLING idle CPU */
 #define TIF_SECCOMP		10	/* secure computing */
 #define TIF_RESTOREALL		11	/* Restore all regs (implies NOERROR) */
 #define TIF_NOERROR		12	/* Force successful syscall return */
@@ -129,6 +130,7 @@ void arch_setup_new_exec(void);
 #define _TIF_PATCH_PENDING	(1<<TIF_PATCH_PENDING)
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
 #define _TIF_SINGLESTEP		(1<<TIF_SINGLESTEP)
+#define _TIF_NOTIFY_IPI		(1<<TIF_NOTIFY_IPI)
 #define _TIF_SECCOMP		(1<<TIF_SECCOMP)
 #define _TIF_RESTOREALL		(1<<TIF_RESTOREALL)
 #define _TIF_NOERROR		(1<<TIF_NOERROR)
-- 
2.34.1