Received-SPF: pass (google.com: domain of linux-kernel+bounces-213807-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.199.223 as permitted sender) client-ip=147.75.199.223;
Received-SPF: Pass (protection.outlook.com: domain of amd.com designates
 165.204.84.17 as permitted sender) receiver=protection.outlook.com;
 client-ip=165.204.84.17; helo=SATLEXMB04.amd.com; pr=C
From: K Prateek Nayak <kprateek.nayak@amd.com>
To: <linux-kernel@vger.kernel.org>
CC: "Gautham R. Shenoy" <gautham.shenoy@amd.com>, K Prateek Nayak
	<kprateek.nayak@amd.com>, Richard Henderson <richard.henderson@linaro.org>,
	Ivan Kokshaysky <ink@jurassic.park.msu.ru>, Matt Turner <mattst88@gmail.com>,
	Russell King <linux@armlinux.org.uk>, Guo Ren <guoren@kernel.org>, "Michal
 Simek" <monstr@monstr.eu>, Dinh Nguyen <dinguyen@kernel.org>, Jonas Bonn
	<jonas@southpole.se>, Stefan Kristiansson
	<stefan.kristiansson@saunalahti.fi>, Stafford Horne <shorne@gmail.com>,
	"James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>, Helge Deller
	<deller@gmx.de>, Michael Ellerman <mpe@ellerman.id.au>, Nicholas Piggin
	<npiggin@gmail.com>, Christophe Leroy <christophe.leroy@csgroup.eu>, "Naveen
 N. Rao" <naveen.n.rao@linux.ibm.com>, Yoshinori Sato
	<ysato@users.sourceforge.jp>, Rich Felker <dalias@libc.org>, "John Paul
 Adrian Glaubitz" <glaubitz@physik.fu-berlin.de>, "David S. Miller"
	<davem@davemloft.net>, Andreas Larsson <andreas@gaisler.com>, Thomas Gleixner
	<tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, Borislav Petkov
	<bp@alien8.de>, Dave Hansen <dave.hansen@linux.intel.com>, "H. Peter Anvin"
	<hpa@zytor.com>, "Rafael J. Wysocki" <rafael@kernel.org>, Daniel Lezcano
	<daniel.lezcano@linaro.org>, Peter Zijlstra <peterz@infradead.org>, "Juri
 Lelli" <juri.lelli@redhat.com>, Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>, Steven Rostedt
	<rostedt@goodmis.org>, Ben Segall <bsegall@google.com>, Mel Gorman
	<mgorman@suse.de>, Daniel Bristot de Oliveira <bristot@redhat.com>, "Valentin
 Schneider" <vschneid@redhat.com>, Andrew Donnellan <ajd@linux.ibm.com>,
	Benjamin Gray <bgray@linux.ibm.com>, Frederic Weisbecker
	<frederic@kernel.org>, Xin Li <xin3.li@intel.com>, Kees Cook
	<keescook@chromium.org>, Rick Edgecombe <rick.p.edgecombe@intel.com>, "Tony
 Battersby" <tonyb@cybernetics.com>, Bjorn Helgaas <bhelgaas@google.com>,
	"Brian Gerst" <brgerst@gmail.com>, Leonardo Bras <leobras@redhat.com>, Imran
 Khan <imran.f.khan@oracle.com>, "Paul E. McKenney" <paulmck@kernel.org>, "Rik
 van Riel" <riel@surriel.com>, Tim Chen <tim.c.chen@linux.intel.com>, David
 Vernet <void@manifault.com>, Julia Lawall <julia.lawall@inria.fr>,
	<linux-alpha@vger.kernel.org>, <linux-arm-kernel@lists.infradead.org>,
	<linux-csky@vger.kernel.org>, <linux-openrisc@vger.kernel.org>,
	<linux-parisc@vger.kernel.org>, <linuxppc-dev@lists.ozlabs.org>,
	<linux-sh@vger.kernel.org>, <sparclinux@vger.kernel.org>,
	<linux-pm@vger.kernel.org>, <x86@kernel.org>
Subject: [PATCH v2 01/14] thread_info: Add helpers to test and clear TIF_NOTIFY_IPI
Date: Thu, 13 Jun 2024 18:16:00 +0000
Message-ID: <20240613181613.4329-2-kprateek.nayak@amd.com>
In-Reply-To: <20240613181613.4329-1-kprateek.nayak@amd.com>
References: <20240613181613.4329-1-kprateek.nayak@amd.com>
Precedence: bulk
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Content-Type: text/plain
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 13 Jun 2024 18:17:32.5335
 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: a2fff5df-6d2e-479b-b436-08dc8bd5180e
X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d
X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com]
X-MS-Exchange-CrossTenant-AuthSource:
	BL6PEPF00022573.namprd02.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Anonymous
X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem
X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW3PR12MB4364

From: "Gautham R. Shenoy" <gautham.shenoy@amd.com>

Introduce the notion of TIF_NOTIFY_IPI flag. When a processor in
TIF_POLLING mode needs to process an IPI, the sender sets NEED_RESCHED
bit in idle task's thread_info to pull the target out of idle and avoids
sending an interrupt to the idle CPU. When NEED_RESCHED is set, the
scheduler assumes that a new task has been queued on the idle CPU and
calls schedule_idle(), however, it is not necessary that an IPI on an
idle CPU will necessarily end up waking a task on the said CPU. To avoid
spurious calls to schedule_idle() assuming an IPI on an idle CPU will
always wake a task on the said CPU, TIF_NOTIFY_IPI will be used to pull
a TIF_POLLING CPU out of idle.

Since the IPI handlers are processed before the call to schedule_idle(),
schedule_idle() will be called only if one of the handlers have woken up
a new task on the CPU and has set NEED_RESCHED.

Add tif_notify_ipi() and current_clr_notify_ipi() helpers to test if
TIF_NOTIFY_IPI is set in the current task's thread_info, and to clear it
respectively. These interfaces will be used in subsequent patches as
TIF_NOTIFY_IPI notion is integrated in the scheduler and in the idle
path.

[ prateek: Split the changes into a separate patch, add commit log ]

Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Guo Ren <guoren@kernel.org>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Dinh Nguyen <dinguyen@kernel.org>
Cc: Jonas Bonn <jonas@southpole.se>
Cc: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
Cc: Stafford Horne <shorne@gmail.com>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Rich Felker <dalias@libc.org>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Andrew Donnellan <ajd@linux.ibm.com>
Cc: Benjamin Gray <bgray@linux.ibm.com>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: Xin Li <xin3.li@intel.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc: Tony Battersby <tonyb@cybernetics.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Leonardo Bras <leobras@redhat.com>
Cc: Imran Khan <imran.f.khan@oracle.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: David Vernet <void@manifault.com>
Cc: Julia Lawall <julia.lawall@inria.fr>
Cc: linux-alpha@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-csky@vger.kernel.org
Cc: linux-openrisc@vger.kernel.org
Cc: linux-parisc@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-sh@vger.kernel.org
Cc: sparclinux@vger.kernel.org
Cc: linux-pm@vger.kernel.org
Cc: x86@kernel.org
Signed-off-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
Co-developed-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
---
v1..v2:
o No changes.
---
 include/linux/thread_info.h | 43 +++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
index 9ea0b28068f4..1e10dd8c0227 100644
--- a/include/linux/thread_info.h
+++ b/include/linux/thread_info.h
@@ -195,6 +195,49 @@ static __always_inline bool tif_need_resched(void)
 
 #endif /* _ASM_GENERIC_BITOPS_INSTRUMENTED_NON_ATOMIC_H */
 
+#ifdef TIF_NOTIFY_IPI
+
+#ifdef _ASM_GENERIC_BITOPS_INSTRUMENTED_NON_ATOMIC_H
+
+static __always_inline bool tif_notify_ipi(void)
+{
+	return arch_test_bit(TIF_NOTIFY_IPI,
+			     (unsigned long *)(&current_thread_info()->flags));
+}
+
+static __always_inline void current_clr_notify_ipi(void)
+{
+	arch_clear_bit(TIF_NOTIFY_IPI,
+		       (unsigned long *)(&current_thread_info()->flags));
+}
+
+#else
+
+static __always_inline bool tif_notify_ipi(void)
+{
+	return test_bit(TIF_NOTIFY_IPI,
+			(unsigned long *)(&current_thread_info()->flags));
+}
+
+static __always_inline void current_clr_notify_ipi(void)
+{
+	clear_bit(TIF_NOTIFY_IPI,
+		  (unsigned long *)(&current_thread_info()->flags));
+}
+
+#endif /* _ASM_GENERIC_BITOPS_INSTRUMENTED_NON_ATOMIC_H */
+
+#else /* !TIF_NOTIFY_IPI */
+
+static __always_inline bool tif_notify_ipi(void)
+{
+	return false;
+}
+
+static __always_inline void current_clr_notify_ipi(void) { }
+
+#endif /* TIF_NOTIFY_IPI */
+
 #ifndef CONFIG_HAVE_ARCH_WITHIN_STACK_FRAMES
 static inline int arch_within_stack_frames(const void * const stack,
 					   const void * const stackend,
-- 
2.34.1