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Message-Id: <20230830184958.2333078-8-ankur.a.arora@oracle.com>
Date: Wed, 30 Aug 2023 11:49:56 -0700
From: Ankur Arora <ankur.a.arora@...cle.com>
To: linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org
Cc: akpm@...ux-foundation.org, luto@...nel.org, bp@...en8.de,
dave.hansen@...ux.intel.com, hpa@...or.com, mingo@...hat.com,
juri.lelli@...hat.com, vincent.guittot@...aro.org,
willy@...radead.org, mgorman@...e.de, peterz@...radead.org,
rostedt@...dmis.org, tglx@...utronix.de, jon.grimm@....com,
bharata@....com, raghavendra.kt@....com,
boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
Ankur Arora <ankur.a.arora@...cle.com>,
Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH v2 7/9] sched: define TIF_ALLOW_RESCHED
On preempt_model_none() or preempt_model_voluntary() configurations
rescheduling of kernel threads happens only when they allow it, and
only at explicit preemption points, via calls to cond_resched() or
similar.
That leaves out contexts where it is not convenient to periodically
call cond_resched() -- for instance when executing a potentially long
running primitive (such as REP; STOSB.)
This means that we either suffer high scheduling latency or avoid
certain constructs.
Define TIF_ALLOW_RESCHED to demarcate such sections.
Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
---
arch/x86/include/asm/thread_info.h | 2 ++
include/linux/sched.h | 30 ++++++++++++++++++++++++++++++
2 files changed, 32 insertions(+)
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index d63b02940747..fc6f4121b412 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -100,6 +100,7 @@ struct thread_info {
#define TIF_BLOCKSTEP 25 /* set when we want DEBUGCTLMSR_BTF */
#define TIF_LAZY_MMU_UPDATES 27 /* task is updating the mmu lazily */
#define TIF_ADDR32 29 /* 32-bit address space on 64 bits */
+#define TIF_RESCHED_ALLOW 30 /* reschedule if needed */
#define _TIF_NOTIFY_RESUME (1 << TIF_NOTIFY_RESUME)
#define _TIF_SIGPENDING (1 << TIF_SIGPENDING)
@@ -122,6 +123,7 @@ struct thread_info {
#define _TIF_BLOCKSTEP (1 << TIF_BLOCKSTEP)
#define _TIF_LAZY_MMU_UPDATES (1 << TIF_LAZY_MMU_UPDATES)
#define _TIF_ADDR32 (1 << TIF_ADDR32)
+#define _TIF_RESCHED_ALLOW (1 << TIF_RESCHED_ALLOW)
/* flags to check in __switch_to() */
#define _TIF_WORK_CTXSW_BASE \
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 177b3f3676ef..4dd3d91d990f 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2245,6 +2245,36 @@ static __always_inline bool need_resched(void)
return unlikely(tif_need_resched());
}
+#ifdef TIF_RESCHED_ALLOW
+/*
+ * allow_resched() .. disallow_resched() demarcate a preemptible section.
+ *
+ * Used around primitives where it might not be convenient to periodically
+ * call cond_resched().
+ */
+static inline void allow_resched(void)
+{
+ might_sleep();
+ set_tsk_thread_flag(current, TIF_RESCHED_ALLOW);
+}
+
+static inline void disallow_resched(void)
+{
+ clear_tsk_thread_flag(current, TIF_RESCHED_ALLOW);
+}
+
+static __always_inline bool resched_allowed(void)
+{
+ return unlikely(test_tsk_thread_flag(current, TIF_RESCHED_ALLOW));
+}
+
+#else
+static __always_inline bool resched_allowed(void)
+{
+ return false;
+}
+#endif /* TIF_RESCHED_ALLOW */
+
/*
* Wrappers for p->thread_info->cpu access. No-op on UP.
*/
--
2.31.1
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