From: Waiman Long <longman@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Jonathan Corbet <corbet@lwn.net>
Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Davidlohr Bueso <dave@stgolabs.net>,
Mike Galbraith <umgwanakikbuti@gmail.com>,
Scott J Norton <scott.norton@hpe.com>,
Waiman Long <longman@redhat.com>
Subject: [PATCH-tip v5 16/21] TP-futex: Enable kernel reader lock stealing
Date: Fri, 3 Feb 2017 13:03:49 -0500 [thread overview]
Message-ID: <1486145034-22210-17-git-send-email-longman@redhat.com> (raw)
In-Reply-To: <1486145034-22210-1-git-send-email-longman@redhat.com>
The TP-futexes prefer writers as the code path is much simpler for
them. This may not be good for overall system performance especially
if there is a fair amount of reader activities.
This patch enables kernel reader to steal the lock when the futex is
currently reader-owned and the lock handoff mechanism hasn't been
enabled yet. A new field locksteal_disabled is added to the futex
state object for controlling reader lock stealing. So the waiting
reader must retrieve the futex state object first before doing it.
Signed-off-by: Waiman Long <longman@redhat.com>
---
kernel/futex.c | 23 +++++++++++++++++++++--
1 file changed, 21 insertions(+), 2 deletions(-)
diff --git a/kernel/futex.c b/kernel/futex.c
index 1f97c85..90c8c80 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -239,6 +239,7 @@ struct futex_state {
atomic_t refcount;
u32 handoff_pid; /* For TP futexes only */
+ int locksteal_disabled; /* For TP futexes only */
enum futex_type type;
union futex_key key;
@@ -3438,6 +3439,7 @@ void exit_robust_list(struct task_struct *curr)
state = alloc_futex_state();
state->type = TYPE_TP;
state->key = *key;
+ state->locksteal_disabled = false;
list_add(&state->fs_list, &hb->fs_head);
WARN_ON(atomic_read(&state->refcount) != 1);
@@ -3783,9 +3785,10 @@ static int futex_spin_on_owner(u32 __user *uaddr, const u32 vpid,
WRITE_ONCE(state->handoff_pid, vpid);
/*
- * Disable handoff check.
+ * Disable handoff check and reader lock
+ * stealing.
*/
- handoff_set = true;
+ state->locksteal_disabled = handoff_set = true;
}
}
@@ -3888,6 +3891,7 @@ static int futex_spin_on_owner(u32 __user *uaddr, const u32 vpid,
*/
WRITE_ONCE(state->mutex_owner, NULL);
WRITE_ONCE(state->handoff_pid, 0);
+ state->locksteal_disabled = false;
preempt_enable();
return (ret < 0) ? ret : TP_STATUS_SLEEP(ret, nsleep);
@@ -3968,6 +3972,21 @@ static noinline int futex_lock(u32 __user *uaddr, unsigned int flags,
goto out_put_state_key;
}
+ /*
+ * For reader, we will try to steal the lock here as if it is the
+ * top waiter without taking the serialization mutex if reader
+ * lock stealing isn't disabled even though the FUTEX_WAITERS bit
+ * is set.
+ */
+ if (shared && !state->locksteal_disabled) {
+ ret = futex_trylock(uaddr, vpid, &uval, true);
+ if (ret) {
+ if (ret > 0)
+ ret = TP_LOCK_STOLEN;
+ goto out_put_state_key;
+ }
+ }
+
if (to)
hrtimer_start_expires(&to->timer, HRTIMER_MODE_ABS);
--
1.8.3.1
next prev parent reply other threads:[~2017-02-03 18:04 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-03 18:03 [PATCH-tip v5 00/21] futex: Introducing throughput-optimized (TP) futexes Waiman Long
2017-02-03 18:03 ` [PATCH-tip v5 01/21] perf bench: New microbenchmark for userspace mutex performance Waiman Long
2017-02-03 18:03 ` [PATCH-tip v5 02/21] perf bench: New microbenchmark for userspace rwlock performance Waiman Long
2017-02-03 18:03 ` [PATCH-tip v5 03/21] futex: Consolidate duplicated timer setup code Waiman Long
2017-02-03 18:03 ` [PATCH-tip v5 04/21] futex: Rename futex_pi_state to futex_state Waiman Long
2017-02-03 18:03 ` [PATCH-tip v5 05/21] futex: Add helpers to get & cmpxchg futex value without lock Waiman Long
2017-02-03 18:03 ` [PATCH-tip v5 06/21] futex: Consolidate pure pi_state_list add & delete codes to helpers Waiman Long
2017-02-03 18:03 ` [PATCH-tip v5 07/21] futex: Add a new futex type field into futex_state Waiman Long
2017-02-03 18:03 ` [PATCH-tip v5 08/21] futex: Allow direct attachment of futex_state objects to hash bucket Waiman Long
2017-02-03 18:03 ` [PATCH-tip v5 09/21] futex: Introduce throughput-optimized (TP) futexes Waiman Long
2017-02-03 18:03 ` [PATCH-tip v5 10/21] TP-futex: Enable robust handling Waiman Long
2017-02-03 18:03 ` [PATCH-tip v5 11/21] TP-futex: Implement lock handoff to prevent lock starvation Waiman Long
2017-02-03 18:03 ` [PATCH-tip v5 12/21] TP-futex: Return status code on FUTEX_LOCK calls Waiman Long
2017-02-03 18:03 ` [PATCH-tip v5 13/21] TP-futex: Add timeout support Waiman Long
2017-02-03 18:03 ` [PATCH-tip v5 14/21] TP-futex, doc: Add TP futexes documentation Waiman Long
2017-02-03 18:03 ` [PATCH-tip v5 15/21] TP-futex: Support userspace reader/writer locks Waiman Long
2017-02-03 18:03 ` Waiman Long [this message]
2017-02-03 18:03 ` [PATCH-tip v5 17/21] TP-futex: Group readers together in wait queue Waiman Long
2017-02-03 18:23 ` valdis.kletnieks
2017-02-03 18:42 ` Waiman Long
2017-02-03 19:26 ` valdis.kletnieks
2017-02-03 18:03 ` [PATCH-tip v5 18/21] TP-futex, doc: Update TP futexes document on shared locking Waiman Long
2017-02-03 18:03 ` [PATCH-tip v5 19/21] perf bench: Extend mutex/rwlock futex suite to test TP futexes Waiman Long
2017-02-03 18:03 ` [PATCH-tip v5 20/21] sched, TP-futex: Make wake_up_q() return wakeup count Waiman Long
2017-02-03 18:03 ` [PATCH-tip v5 21/21] futex: Dump internal futex state via debugfs Waiman Long
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