[PATCH v2 05/14] arm/thread_info: Introduce TIF_NOTIFY_IPI flag

K Prateek Nayak
2024-06-13T18:19:31Z

Add support for TIF_NOTIFY_IPI on ARM. 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: Russell King <linux@armlinux.org.uk>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Ingo Molnar <mingo@redhat.com>
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: Linus Walleij <linus.walleij@linaro.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-pm@vger.kernel.org
Link: https://github.com/antonblanchard/ipistorm [1]
Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
---
v1..v2:
o Dropped the ARM benchmark numbers since I could not get my hands on an
ARM64 server internally. I tested if the lack of TIF_NOTIFY_IPI
triggers any of the modified path or not on x86 by only applying till
Patch 3 and I did not see anything unexpected. I'll update the thread
with the results from the ARM server [if and] when I get my hands on
it again.
---
arch/arm/include/asm/thread_info.h | 3 +++
1 file changed, 3 insertions(+)

diff --git a/arch/arm/include/asm/thread_info.h b/arch/arm/include/asm/thread_info.h
index 943ffcf069d2..324248d87c9e 100644
--- a/arch/arm/include/asm/thread_info.h
+++ b/arch/arm/include/asm/thread_info.h
@@ -136,6 +136,7 @@ extern int vfp_restore_user_hwstate(struct user_vfp *,
* thread information flags:
* TIF_USEDFPU - FPU was used by this task this quantum (SMP)
* TIF_POLLING_NRFLAG - true if poll_idle() is polling TIF_NEED_RESCHED
+ * or TIF_NOTIFY_IPI
*
* Any bit in the range of 0..15 will cause do_work_pending() to be invoked.
*/
@@ -144,6 +145,7 @@ extern int vfp_restore_user_hwstate(struct user_vfp *,
#define TIF_NOTIFY_RESUME 2 /* callback before returning to user */
#define TIF_UPROBE 3 /* breakpointed or singlestepping */
#define TIF_NOTIFY_SIGNAL 4 /* signal notifications exist */
+#define TIF_NOTIFY_IPI 5 /* pending IPI on TIF_POLLLING idle CPU */

#define TIF_USING_IWMMXT 17
#define TIF_MEMDIE 18 /* is terminating due to OOM killer */
@@ -164,6 +166,7 @@ extern int vfp_restore_user_hwstate(struct user_vfp *,
#define _TIF_SECCOMP (1 << TIF_SECCOMP)
#define _TIF_NOTIFY_SIGNAL (1 << TIF_NOTIFY_SIGNAL)
#define _TIF_USING_IWMMXT (1 << TIF_USING_IWMMXT)
+#define _TIF_NOTIFY_IPI (1 << TIF_NOTIFY_IPI)

/* Checks for any syscall work in entry-common.S */
#define _TIF_SYSCALL_WORK (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
--
2.34.1