From: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
To: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
virtualization@lists.linux-foundation.org,
linux-s390@vger.kernel.org,
xen-devel-request@lists.xenproject.org, kvm@vger.kernel.org
Cc: benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au,
mingo@redhat.com, peterz@infradead.org,
paulmck@linux.vnet.ibm.com, will.deacon@arm.com,
kernellwp@gmail.com, jgross@suse.com, pbonzini@redhat.com,
bsingharora@gmail.com, boqun.feng@gmail.com,
borntraeger@de.ibm.com,
Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
Subject: [PATCH v4 2/5] locking/osq: Drop the overload of osq_lock()
Date: Wed, 19 Oct 2016 06:20:13 -0400 [thread overview]
Message-ID: <1476872416-42752-3-git-send-email-xinhui.pan@linux.vnet.ibm.com> (raw)
In-Reply-To: <1476872416-42752-1-git-send-email-xinhui.pan@linux.vnet.ibm.com>
An over-committed guest with more vCPUs than pCPUs has a heavy overload in
osq_lock().
This is because vCPU A hold the osq lock and yield out, vCPU B wait per_cpu
node->locked to be set. IOW, vCPU B wait vCPU A to run and unlock the osq
lock.
Kernel has an interface bool vcpu_is_preempted(int cpu) to see if a vCPU is
currently running or not. So break the spin loops on true condition.
test case:
perf record -a perf bench sched messaging -g 400 -p && perf report
before patch:
18.09% sched-messaging [kernel.vmlinux] [k] osq_lock
12.28% sched-messaging [kernel.vmlinux] [k] rwsem_spin_on_owner
5.27% sched-messaging [kernel.vmlinux] [k] mutex_unlock
3.89% sched-messaging [kernel.vmlinux] [k] wait_consider_task
3.64% sched-messaging [kernel.vmlinux] [k] _raw_write_lock_irq
3.41% sched-messaging [kernel.vmlinux] [k] mutex_spin_on_owner.is
2.49% sched-messaging [kernel.vmlinux] [k] system_call
after patch:
20.68% sched-messaging [kernel.vmlinux] [k] mutex_spin_on_owner
8.45% sched-messaging [kernel.vmlinux] [k] mutex_unlock
4.12% sched-messaging [kernel.vmlinux] [k] system_call
3.01% sched-messaging [kernel.vmlinux] [k] system_call_common
2.83% sched-messaging [kernel.vmlinux] [k] copypage_power7
2.64% sched-messaging [kernel.vmlinux] [k] rwsem_spin_on_owner
2.00% sched-messaging [kernel.vmlinux] [k] osq_lock
Suggested-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
---
kernel/locking/osq_lock.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c
index 05a3785..39d1385 100644
--- a/kernel/locking/osq_lock.c
+++ b/kernel/locking/osq_lock.c
@@ -21,6 +21,11 @@ static inline int encode_cpu(int cpu_nr)
return cpu_nr + 1;
}
+static inline int node_cpu(struct optimistic_spin_node *node)
+{
+ return node->cpu - 1;
+}
+
static inline struct optimistic_spin_node *decode_cpu(int encoded_cpu_val)
{
int cpu_nr = encoded_cpu_val - 1;
@@ -118,8 +123,11 @@ bool osq_lock(struct optimistic_spin_queue *lock)
while (!READ_ONCE(node->locked)) {
/*
* If we need to reschedule bail... so we can block.
+ * Use vcpu_is_preempted to detech lock holder preemption issue
+ * and break. vcpu_is_preempted is a macro defined by false if
+ * arch does not support vcpu preempted check,
*/
- if (need_resched())
+ if (need_resched() || vcpu_is_preempted(node_cpu(node->prev)))
goto unqueue;
cpu_relax_lowlatency();
--
2.4.11
next prev parent reply other threads:[~2016-10-19 6:22 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-19 10:20 [PATCH v4 0/5] implement vcpu preempted check Pan Xinhui
2016-10-19 6:47 ` Christian Borntraeger
2016-10-19 16:57 ` Pan Xinhui
2016-10-19 10:20 ` [PATCH v4 1/5] kernel/sched: introduce vcpu preempted check interface Pan Xinhui
2016-10-19 10:20 ` Pan Xinhui [this message]
2016-10-19 10:20 ` [PATCH v4 3/5] kernel/locking: Drop the overload of {mutex, rwsem}_spin_on_owner Pan Xinhui
2016-10-19 10:20 ` [PATCH v4 4/5] powerpc/spinlock: support vcpu preempted check Pan Xinhui
2016-10-19 10:20 ` [PATCH v4 5/5] x86, kvm: " Pan Xinhui
2016-10-19 17:24 ` Radim Krčmář
2016-10-19 18:45 ` Pan Xinhui
2016-10-24 14:39 ` Paolo Bonzini
2016-10-24 15:14 ` Radim Krčmář
2016-10-24 15:18 ` Paolo Bonzini
2016-10-25 1:25 ` Pan Xinhui
2016-10-19 15:58 ` [PATCH v4 0/5] implement " Juergen Gross
2016-10-19 17:08 ` Pan Xinhui
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