From: Eric Dumazet <eric.dumazet@gmail.com>
To: ben@iagu.net, Thomas Gleixner <tglx@linutronix.de>
Cc: Avi Kivity <avi@redhat.com>, KVM list <kvm@vger.kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
John Stultz <johnstul@us.ibm.com>,
Richard Cochran <richard.cochran@omicron.at>
Subject: [PATCH] posix-timers: RCU conversion
Date: Tue, 22 Mar 2011 08:09:20 +0100 [thread overview]
Message-ID: <1300777760.2837.38.camel@edumazet-laptop> (raw)
In-Reply-To: <1300746429.2837.20.camel@edumazet-laptop>
Ben Nagy reported a scalability problem with KVM/QEMU that hit very hard
a single spinlock (idr_lock) in posix-timers code, on its 48 core
machine.
Even on a 16 cpu machine (2x4x2), a single test can show 98% of cpu time
used in ticket_spin_lock, from lock_timer
Ref: http://www.spinics.net/lists/kvm/msg51526.html
Switching to RCU is quite easy, IDR being already RCU ready.
idr_lock should be locked only for an insert/delete, not a lookup.
Benchmark on a 2x4x2 machine, 16 processes calling timer_gettime().
Before :
real 1m18.669s
user 0m1.346s
sys 1m17.180s
After :
real 0m3.296s
user 0m1.366s
sys 0m1.926s
Reported-by: Ben Nagy <ben@iagu.net>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <johnstul@us.ibm.com>
Cc: Richard Cochran <richard.cochran@omicron.at>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
include/linux/posix-timers.h | 1 +
kernel/posix-timers.c | 25 ++++++++++++++-----------
2 files changed, 15 insertions(+), 11 deletions(-)
diff --git a/include/linux/posix-timers.h b/include/linux/posix-timers.h
index d51243a..5dc27ca 100644
--- a/include/linux/posix-timers.h
+++ b/include/linux/posix-timers.h
@@ -81,6 +81,7 @@ struct k_itimer {
unsigned long expires;
} mmtimer;
} it;
+ struct rcu_head rcu;
};
struct k_clock {
diff --git a/kernel/posix-timers.c b/kernel/posix-timers.c
index 4c01249..acb9be9 100644
--- a/kernel/posix-timers.c
+++ b/kernel/posix-timers.c
@@ -491,6 +491,13 @@ static struct k_itimer * alloc_posix_timer(void)
return tmr;
}
+static void k_itimer_rcu_free(struct rcu_head *head)
+{
+ struct k_itimer *tmr = container_of(head, struct k_itimer, rcu);
+
+ kmem_cache_free(posix_timers_cache, tmr);
+}
+
#define IT_ID_SET 1
#define IT_ID_NOT_SET 0
static void release_posix_timer(struct k_itimer *tmr, int it_id_set)
@@ -503,7 +510,7 @@ static void release_posix_timer(struct k_itimer *tmr, int it_id_set)
}
put_pid(tmr->it_pid);
sigqueue_free(tmr->sigq);
- kmem_cache_free(posix_timers_cache, tmr);
+ call_rcu(&tmr->rcu, k_itimer_rcu_free);
}
static struct k_clock *clockid_to_kclock(const clockid_t id)
@@ -631,22 +638,18 @@ out:
static struct k_itimer *__lock_timer(timer_t timer_id, unsigned long *flags)
{
struct k_itimer *timr;
- /*
- * Watch out here. We do a irqsave on the idr_lock and pass the
- * flags part over to the timer lock. Must not let interrupts in
- * while we are moving the lock.
- */
- spin_lock_irqsave(&idr_lock, *flags);
+
+ rcu_read_lock();
timr = idr_find(&posix_timers_id, (int)timer_id);
if (timr) {
- spin_lock(&timr->it_lock);
+ spin_lock_irqsave(&timr->it_lock, *flags);
if (timr->it_signal == current->signal) {
- spin_unlock(&idr_lock);
+ rcu_read_unlock();
return timr;
}
- spin_unlock(&timr->it_lock);
+ spin_unlock_irqrestore(&timr->it_lock, *flags);
}
- spin_unlock_irqrestore(&idr_lock, *flags);
+ rcu_read_unlock();
return NULL;
}
next prev parent reply other threads:[~2011-03-22 7:12 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <AANLkTikZZ4MXZjx_+6u-vKVSgxULQo2BkQKRO6K_vzFy@mail.gmail.com>
[not found] ` <20110318123031.GB6066@8bytes.org>
[not found] ` <AANLkTin2k1ZSLa0NG6pKBvHYnKEV21t8pEqzeJWNn_rR@mail.gmail.com>
[not found] ` <4D871F6C.40207@redhat.com>
[not found] ` <AANLkTintxnKRQ4rD4Wo8_MHU4yJVzYaRhR=GjnDMGwNj@mail.gmail.com>
[not found] ` <AANLkTin8ZoUAVR2ajoV6cBFiUSe_Dof0_k60dcAGW3r-@mail.gmail.com>
[not found] ` <4D875842.9050308@redhat.com>
[not found] ` <AANLkTikWQS281kTtJ32-qo5U+w_BAak7qUwVhUQgOxxv@mail.gmail.com>
[not found] ` <4D8773AA.8030408@redhat.com>
[not found] ` <AANLkTin3Si1EAa=Va6f45vW-tYQ1Yk8dETXpHJHHHkxe@mail.gmail.com>
[not found] ` <1300726498.2884.493.camel@edumazet-laptop>
[not found] ` <4D8784A9.8040303@redhat.com>
[not found] ` <1300727545.2884.513.camel@edumazet-laptop>
[not found] ` <AANLkTinn7OKKKvBYe7KWsrReuYDdma5+8gHJHXdCacDY@mail.gmail.com>
2011-03-21 22:27 ` [RFC] posix-timers: RCU conversion Eric Dumazet
2011-03-22 7:09 ` Eric Dumazet [this message]
2011-03-22 8:59 ` [PATCH] " Ben Nagy
2011-03-22 10:35 ` Avi Kivity
2011-04-04 3:30 ` Ben Nagy
2011-04-04 7:18 ` Avi Kivity
2011-04-05 7:49 ` Peter Zijlstra
2011-04-05 8:16 ` Avi Kivity
2011-04-05 8:48 ` Peter Zijlstra
2011-04-05 8:56 ` Avi Kivity
2011-04-05 9:03 ` Peter Zijlstra
2011-04-05 9:08 ` Avi Kivity
2011-04-05 9:50 ` Ben Nagy
2011-04-05 8:56 ` Mike Galbraith
2011-04-03 16:54 ` Eric Dumazet
2011-04-04 18:08 ` john stultz
2011-04-04 19:47 ` Eric Dumazet
2011-04-05 14:48 ` Oleg Nesterov
2011-04-05 15:18 ` [PATCH v2] " Eric Dumazet
2011-04-05 15:43 ` Oleg Nesterov
2011-05-16 15:10 ` Avi Kivity
2011-05-16 15:30 ` Eric Dumazet
2011-04-08 18:28 ` [PATCH] " Paul E. McKenney
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