From: "Gautham R. Shenoy" <gautham.she...@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.hender...@linaro.org>
Cc: Ivan Kokshaysky <i...@jurassic.park.msu.ru>
Cc: Matt Turner <matts...@gmail.com>
Cc: Russell King <li...@armlinux.org.uk>
Cc: Guo Ren <guo...@kernel.org>
Cc: Michal Simek <mon...@monstr.eu>
Cc: Dinh Nguyen <dingu...@kernel.org>
Cc: Jonas Bonn <jo...@southpole.se>
Cc: Stefan Kristiansson <stefan.kristians...@saunalahti.fi>
Cc: Stafford Horne <sho...@gmail.com>
Cc: "James E.J. Bottomley" <james.bottom...@hansenpartnership.com>
Cc: Helge Deller <del...@gmx.de>
Cc: Michael Ellerman <m...@ellerman.id.au>
Cc: Nicholas Piggin <npig...@gmail.com>
Cc: Christophe Leroy <christophe.le...@csgroup.eu>
Cc: "Aneesh Kumar K.V" <aneesh.ku...@kernel.org>
Cc: "Naveen N. Rao" <naveen.n....@linux.ibm.com>
Cc: Yoshinori Sato <ys...@users.sourceforge.jp>
Cc: Rich Felker <dal...@libc.org>
Cc: John Paul Adrian Glaubitz <glaub...@physik.fu-berlin.de>
Cc: "David S. Miller" <da...@davemloft.net>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Ingo Molnar <mi...@redhat.com>
Cc: Borislav Petkov <b...@alien8.de>
Cc: Dave Hansen <dave.han...@linux.intel.com>
Cc: "H. Peter Anvin" <h...@zytor.com>
Cc: "Rafael J. Wysocki" <raf...@kernel.org>
Cc: Daniel Lezcano <daniel.lezc...@linaro.org>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Juri Lelli <juri.le...@redhat.com>
Cc: Vincent Guittot <vincent.guit...@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggem...@arm.com>
Cc: Steven Rostedt <rost...@goodmis.org>
Cc: Ben Segall <bseg...@google.com>
Cc: Mel Gorman <mgor...@suse.de>
Cc: Daniel Bristot de Oliveira <bris...@redhat.com>
Cc: Valentin Schneider <vschn...@redhat.com>
Cc: Al Viro <v...@zeniv.linux.org.uk>
Cc: Linus Walleij <linus.wall...@linaro.org>
Cc: Ard Biesheuvel <a...@kernel.org>
Cc: Andrew Donnellan <a...@linux.ibm.com>
Cc: Nicholas Miehlbradt <nicho...@linux.ibm.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Arnd Bergmann <a...@arndb.de>
Cc: Josh Poimboeuf <jpoim...@kernel.org>
Cc: "Kirill A. Shutemov" <kirill.shute...@linux.intel.com>
Cc: Rick Edgecombe <rick.p.edgeco...@intel.com>
Cc: Tony Battersby <to...@cybernetics.com>
Cc: Brian Gerst <brge...@gmail.com>
Cc: Tim Chen <tim.c.c...@linux.intel.com>
Cc: David Vernet <v...@manifault.com>
Cc: x...@kernel.org
Cc: linux-ker...@vger.kernel.org
Cc: linux-alpha@vger.kernel.org
Cc: linux-arm-ker...@lists.infradead.org
Cc: linux-c...@vger.kernel.org
Cc: linux-openr...@vger.kernel.org
Cc: linux-par...@vger.kernel.org
Cc: linuxppc-...@lists.ozlabs.org
Cc: linux...@vger.kernel.org
Cc: sparcli...@vger.kernel.org
Cc: linux...@vger.kernel.org
Signed-off-by: Gautham R. Shenoy <gautham.she...@amd.com>
Co-developed-by: K Prateek Nayak <kprateek.na...@amd.com>
Signed-off-by: K Prateek Nayak <kprateek.na...@amd.com>
---
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 *)(¤t_thread_info()->flags));
+}
+
+static __always_inline void current_clr_notify_ipi(void)
+{
+ arch_clear_bit(TIF_NOTIFY_IPI,
+ (unsigned long *)(¤t_thread_info()->flags));
+}
+
+#else
+
+static __always_inline bool tif_notify_ipi(void)
+{
+ return test_bit(TIF_NOTIFY_IPI,
+ (unsigned long *)(¤t_thread_info()->flags));
+}
+
+static __always_inline void current_clr_notify_ipi(void)
+{
+ clear_bit(TIF_NOTIFY_IPI,
+ (unsigned long *)(¤t_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
