From: Nicholas Piggin <npiggin@gmail.com>
To: linux-arch@vger.kernel.org
Cc: Nicholas Piggin <npiggin@gmail.com>,
x86@kernel.org,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Arnd Bergmann <arnd@arndb.de>,
Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-mm@kvack.org, Anton Blanchard <anton@ozlabs.org>
Subject: [RFC PATCH 6/7] lazy tlb: allow lazy tlb mm switching to be configurable
Date: Fri, 10 Jul 2020 11:56:45 +1000 [thread overview]
Message-ID: <20200710015646.2020871-7-npiggin@gmail.com> (raw)
In-Reply-To: <20200710015646.2020871-1-npiggin@gmail.com>
NOMMU systems could easily go without this and save a bit of code
and the mm refcounting, because their mm switch is a no-op. I haven't
flipped them over because haven't audited all arch code to convert
over to using the _lazy_tlb refcounting.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
arch/Kconfig | 7 +++++
include/linux/sched/mm.h | 12 ++++++---
kernel/sched/core.c | 55 +++++++++++++++++++++++++++-------------
kernel/sched/sched.h | 4 ++-
4 files changed, 55 insertions(+), 23 deletions(-)
diff --git a/arch/Kconfig b/arch/Kconfig
index 8cc35dc556c7..2daf8fe6146a 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -411,6 +411,13 @@ config MMU_GATHER_NO_GATHER
bool
depends on MMU_GATHER_TABLE_FREE
+# Would like to make this depend on MMU, because there is little use for lazy mm switching
+# with NOMMU, but have to audit NOMMU architecture code first.
+config MMU_LAZY_TLB
+ def_bool y
+ help
+ Enable "lazy TLB" mmu context switching for kernel threads.
+
config ARCH_HAVE_NMI_SAFE_CMPXCHG
bool
diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
index 110d4ad21de6..2c2b20e2ccc7 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -53,18 +53,22 @@ void mmdrop(struct mm_struct *mm);
/* Helpers for lazy TLB mm refcounting */
static inline void mmgrab_lazy_tlb(struct mm_struct *mm)
{
- mmgrab(mm);
+ if (IS_ENABLED(CONFIG_MMU_LAZY_TLB))
+ mmgrab(mm);
}
static inline void mmdrop_lazy_tlb(struct mm_struct *mm)
{
- mmdrop(mm);
+ if (IS_ENABLED(CONFIG_MMU_LAZY_TLB))
+ mmdrop(mm);
}
static inline void mmdrop_lazy_tlb_smp_mb(struct mm_struct *mm)
{
- /* This depends on mmdrop providing a full smp_mb() */
- mmdrop(mm);
+ if (IS_ENABLED(CONFIG_MMU_LAZY_TLB))
+ mmdrop(mm); /* This depends on mmdrop providing a full smp_mb() */
+ else
+ smp_mb();
}
/*
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d19f2f517f6c..14b4fae6f6e3 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3253,7 +3253,7 @@ static struct rq *finish_task_switch(struct task_struct *prev)
__releases(rq->lock)
{
struct rq *rq = this_rq();
- struct mm_struct *mm = rq->prev_mm;
+ struct mm_struct *mm = NULL;
long prev_state;
/*
@@ -3272,7 +3272,10 @@ static struct rq *finish_task_switch(struct task_struct *prev)
current->comm, current->pid, preempt_count()))
preempt_count_set(FORK_PREEMPT_COUNT);
- rq->prev_mm = NULL;
+#ifdef CONFIG_MMU_LAZY_TLB
+ mm = rq->prev_lazy_mm;
+ rq->prev_lazy_mm = NULL;
+#endif
/*
* A task struct has one reference for the use as "current".
@@ -3393,22 +3396,11 @@ asmlinkage __visible void schedule_tail(struct task_struct *prev)
calculate_sigpending();
}
-/*
- * context_switch - switch to the new MM and the new thread's register state.
- */
-static __always_inline struct rq *
-context_switch(struct rq *rq, struct task_struct *prev,
- struct task_struct *next, struct rq_flags *rf)
+static __always_inline void
+context_switch_mm(struct rq *rq, struct task_struct *prev,
+ struct task_struct *next)
{
- prepare_task_switch(rq, prev, next);
-
- /*
- * For paravirt, this is coupled with an exit in switch_to to
- * combine the page table reload and the switch backend into
- * one hypercall.
- */
- arch_start_context_switch(prev);
-
+#ifdef CONFIG_MMU_LAZY_TLB
/*
* kernel -> kernel lazy + transfer active
* user -> kernel lazy + mmgrab_lazy_tlb() active
@@ -3440,10 +3432,37 @@ context_switch(struct rq *rq, struct task_struct *prev,
exit_lazy_tlb(prev->active_mm, next);
/* will mmdrop_lazy_tlb() in finish_task_switch(). */
- rq->prev_mm = prev->active_mm;
+ rq->prev_lazy_mm = prev->active_mm;
prev->active_mm = NULL;
}
}
+#else
+ if (!next->mm)
+ next->active_mm = &init_mm;
+ membarrier_switch_mm(rq, prev->active_mm, next->active_mm);
+ switch_mm_irqs_off(prev->active_mm, next->active_mm, next);
+ if (!prev->mm)
+ prev->active_mm = NULL;
+#endif
+}
+
+/*
+ * context_switch - switch to the new MM and the new thread's register state.
+ */
+static __always_inline struct rq *
+context_switch(struct rq *rq, struct task_struct *prev,
+ struct task_struct *next, struct rq_flags *rf)
+{
+ prepare_task_switch(rq, prev, next);
+
+ /*
+ * For paravirt, this is coupled with an exit in switch_to to
+ * combine the page table reload and the switch backend into
+ * one hypercall.
+ */
+ arch_start_context_switch(prev);
+
+ context_switch_mm(rq, prev, next);
rq->clock_update_flags &= ~(RQCF_ACT_SKIP|RQCF_REQ_SKIP);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 877fb08eb1b0..b196dd885d33 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -929,7 +929,9 @@ struct rq {
struct task_struct *idle;
struct task_struct *stop;
unsigned long next_balance;
- struct mm_struct *prev_mm;
+#ifdef CONFIG_MMU_LAZY_TLB
+ struct mm_struct *prev_lazy_mm;
+#endif
unsigned int clock_update_flags;
u64 clock;
--
2.23.0
next prev parent reply other threads:[~2020-07-10 1:57 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-10 1:56 [RFC PATCH 0/7] mmu context cleanup, lazy tlb cleanup, Nicholas Piggin
2020-07-10 1:56 ` [RFC PATCH 1/7] asm-generic: add generic MMU versions of mmu context functions Nicholas Piggin
2020-07-10 1:56 ` [RFC PATCH 2/7] arch: use asm-generic mmu context for no-op implementations Nicholas Piggin
2020-07-10 1:56 ` [RFC PATCH 3/7] mm: introduce exit_lazy_tlb Nicholas Piggin
2020-07-10 1:56 ` [RFC PATCH 4/7] x86: use exit_lazy_tlb rather than membarrier_mm_sync_core_before_usermode Nicholas Piggin
2020-07-10 9:42 ` Peter Zijlstra
2020-07-10 14:02 ` Mathieu Desnoyers
2020-07-10 17:04 ` Andy Lutomirski
2020-07-13 4:45 ` Nicholas Piggin
2020-07-13 13:47 ` Nicholas Piggin
2020-07-13 14:13 ` Mathieu Desnoyers
2020-07-13 15:48 ` Andy Lutomirski
2020-07-13 16:37 ` Nicholas Piggin
2020-07-16 4:15 ` Nicholas Piggin
2020-07-16 4:42 ` Nicholas Piggin
2020-07-16 15:46 ` Mathieu Desnoyers
2020-07-16 16:03 ` Mathieu Desnoyers
2020-07-16 18:58 ` Mathieu Desnoyers
2020-07-16 21:24 ` Alan Stern
2020-07-17 13:39 ` Mathieu Desnoyers
2020-07-17 14:51 ` Alan Stern
2020-07-17 15:39 ` Mathieu Desnoyers
2020-07-17 16:11 ` Alan Stern
2020-07-17 16:22 ` Mathieu Desnoyers
2020-07-17 17:44 ` Alan Stern
2020-07-17 17:52 ` Mathieu Desnoyers
2020-07-17 0:00 ` Nicholas Piggin
2020-07-16 5:18 ` Andy Lutomirski
2020-07-16 6:06 ` Nicholas Piggin
2020-07-16 8:50 ` Peter Zijlstra
2020-07-16 10:03 ` Nicholas Piggin
2020-07-16 11:00 ` peterz
2020-07-16 15:34 ` Mathieu Desnoyers
2020-07-16 23:26 ` Nicholas Piggin
2020-07-17 13:42 ` Mathieu Desnoyers
2020-07-20 3:03 ` Nicholas Piggin
2020-07-20 16:46 ` Mathieu Desnoyers
2020-07-21 10:04 ` Nicholas Piggin
2020-07-21 13:11 ` Mathieu Desnoyers
2020-07-21 14:30 ` Nicholas Piggin
2020-07-21 15:06 ` peterz
2020-07-21 15:15 ` Mathieu Desnoyers
2020-07-21 15:19 ` Peter Zijlstra
2020-07-21 15:22 ` Mathieu Desnoyers
2020-07-10 1:56 ` [RFC PATCH 5/7] lazy tlb: introduce lazy mm refcount helper functions Nicholas Piggin
2020-07-10 9:48 ` Peter Zijlstra
2020-07-10 1:56 ` Nicholas Piggin [this message]
2020-07-10 1:56 ` [RFC PATCH 7/7] lazy tlb: shoot lazies, a non-refcounting lazy tlb option Nicholas Piggin
2020-07-10 9:35 ` Peter Zijlstra
2020-07-13 4:58 ` Nicholas Piggin
2020-07-13 15:59 ` Andy Lutomirski
2020-07-13 16:48 ` Nicholas Piggin
2020-07-13 18:18 ` Andy Lutomirski
2020-07-14 5:04 ` Nicholas Piggin
2020-07-14 6:31 ` Nicholas Piggin
2020-07-14 12:46 ` Andy Lutomirski
2020-07-14 13:23 ` Peter Zijlstra
2020-07-16 2:26 ` Nicholas Piggin
2020-07-16 2:35 ` Nicholas Piggin
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