linux-kernel - [PATCH v2 4/5] riscv: add lazy preempt support

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Date:   Thu,  1 Sep 2022 01:59:19 +0800
From:   Jisheng Zhang <jszhang@...nel.org>
To:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <anup@...infault.org>,
        Atish Patra <atishp@...shpatra.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, kvm-riscv@...ts.infradead.org
Subject: [PATCH v2 4/5] riscv: add lazy preempt support

Implement the lazy preempt for riscv.

Signed-off-by: Jisheng Zhang <jszhang@...nel.org>
---
 arch/riscv/Kconfig                   | 1 +
 arch/riscv/include/asm/thread_info.h | 7 +++++--
 arch/riscv/kernel/asm-offsets.c      | 1 +
 arch/riscv/kernel/entry.S            | 9 +++++++--
 4 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 7a8134fd7ec9..9f2f1936b1b5 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -105,6 +105,7 @@ config RISCV
 	select HAVE_PERF_REGS
 	select HAVE_PERF_USER_STACK_DUMP
 	select HAVE_POSIX_CPU_TIMERS_TASK_WORK
+	select HAVE_PREEMPT_LAZY
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_FUNCTION_ARG_ACCESS_API
 	select HAVE_STACKPROTECTOR
diff --git a/arch/riscv/include/asm/thread_info.h b/arch/riscv/include/asm/thread_info.h
index 78933ac04995..471915b179a2 100644
--- a/arch/riscv/include/asm/thread_info.h
+++ b/arch/riscv/include/asm/thread_info.h
@@ -56,6 +56,7 @@
 struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	int                     preempt_count;  /* 0=>preemptible, <0=>BUG */
+	int			preempt_lazy_count;  /* 0=>preemptible, <0=>BUG */
 	/*
 	 * These stack pointers are overwritten on every system call or
 	 * exception.  SP is also saved to the stack it can be recovered when
@@ -90,7 +91,7 @@ struct thread_info {
 #define TIF_NOTIFY_RESUME	1	/* callback before returning to user */
 #define TIF_SIGPENDING		2	/* signal pending */
 #define TIF_NEED_RESCHED	3	/* rescheduling necessary */
-#define TIF_RESTORE_SIGMASK	4	/* restore signal mask in do_signal() */
+#define TIF_NEED_RESCHED_LAZY	4	/* lazy rescheduling */
 #define TIF_MEMDIE		5	/* is terminating due to OOM killer */
 #define TIF_SYSCALL_TRACEPOINT  6       /* syscall tracepoint instrumentation */
 #define TIF_SYSCALL_AUDIT	7	/* syscall auditing */
@@ -98,6 +99,7 @@ struct thread_info {
 #define TIF_NOTIFY_SIGNAL	9	/* signal notifications exist */
 #define TIF_UPROBE		10	/* uprobe breakpoint or singlestep */
 #define TIF_32BIT		11	/* compat-mode 32bit process */
+#define TIF_RESTORE_SIGMASK	12	/* restore signal mask in do_signal() */
 
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_NOTIFY_RESUME	(1 << TIF_NOTIFY_RESUME)
@@ -108,10 +110,11 @@ struct thread_info {
 #define _TIF_SECCOMP		(1 << TIF_SECCOMP)
 #define _TIF_NOTIFY_SIGNAL	(1 << TIF_NOTIFY_SIGNAL)
 #define _TIF_UPROBE		(1 << TIF_UPROBE)
+#define _TIF_NEED_RESCHED_LAZY	(1 << TIF_NEED_RESCHED_LAZY)
 
 #define _TIF_WORK_MASK \
 	(_TIF_NOTIFY_RESUME | _TIF_SIGPENDING | _TIF_NEED_RESCHED | \
-	 _TIF_NOTIFY_SIGNAL | _TIF_UPROBE)
+	 _TIF_NEED_RESCHED_LAZY | _TIF_NOTIFY_SIGNAL | _TIF_UPROBE)
 
 #define _TIF_SYSCALL_WORK \
 	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_TRACEPOINT | _TIF_SYSCALL_AUDIT | \
diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c
index df9444397908..e38e33822f72 100644
--- a/arch/riscv/kernel/asm-offsets.c
+++ b/arch/riscv/kernel/asm-offsets.c
@@ -35,6 +35,7 @@ void asm_offsets(void)
 	OFFSET(TASK_THREAD_S11, task_struct, thread.s[11]);
 	OFFSET(TASK_TI_FLAGS, task_struct, thread_info.flags);
 	OFFSET(TASK_TI_PREEMPT_COUNT, task_struct, thread_info.preempt_count);
+	OFFSET(TASK_TI_PREEMPT_LAZY_COUNT, task_struct, thread_info.preempt_lazy_count);
 	OFFSET(TASK_TI_KERNEL_SP, task_struct, thread_info.kernel_sp);
 	OFFSET(TASK_TI_USER_SP, task_struct, thread_info.user_sp);
 
diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
index b9eda3fcbd6d..595100a4c2c7 100644
--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -361,9 +361,14 @@ restore_all:
 resume_kernel:
 	REG_L s0, TASK_TI_PREEMPT_COUNT(tp)
 	bnez s0, restore_all
-	REG_L s0, TASK_TI_FLAGS(tp)
-	andi s0, s0, _TIF_NEED_RESCHED
+	REG_L s1, TASK_TI_FLAGS(tp)
+	andi s0, s1, _TIF_NEED_RESCHED
+	bnez s0, 1f
+	REG_L s0, TASK_TI_PREEMPT_LAZY_COUNT(tp)
+	bnez s0, restore_all
+	andi s0, s1, _TIF_NEED_RESCHED_LAZY
 	beqz s0, restore_all
+1:
 	call preempt_schedule_irq
 	j restore_all
 #endif
-- 
2.34.1