From 5aff60a191e579ae00ae5ca6ce16c13b687bc8a3 Mon Sep 17 00:00:00 2001 From: Pan Xinhui Date: Wed, 2 Nov 2016 05:08:29 -0400 Subject: locking/osq: Break out of spin-wait busy waiting loop for a preempted vCPU in osq_lock() An over-committed guest with more vCPUs than pCPUs has a heavy overload in osq_lock(). This is because if vCPU-A holds the osq lock and yields out, vCPU-B ends up waiting for per_cpu node->locked to be set. IOW, vCPU-B waits for vCPU-A to run and unlock the osq lock. Use the new vcpu_is_preempted(cpu) interface to detect if a vCPU is currently running or not, and break out of the spin-loop if so. 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 Tested-by: Juergen Gross Signed-off-by: Pan Xinhui Signed-off-by: Peter Zijlstra (Intel) Acked-by: Christian Borntraeger Acked-by: Paolo Bonzini Cc: David.Laight@ACULAB.COM Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: benh@kernel.crashing.org Cc: bsingharora@gmail.com Cc: dave@stgolabs.net Cc: kernellwp@gmail.com Cc: konrad.wilk@oracle.com Cc: linuxppc-dev@lists.ozlabs.org Cc: mpe@ellerman.id.au Cc: paulmck@linux.vnet.ibm.com Cc: paulus@samba.org Cc: rkrcmar@redhat.com Cc: virtualization@lists.linux-foundation.org Cc: will.deacon@arm.com Cc: xen-devel-request@lists.xenproject.org Cc: xen-devel@lists.xenproject.org Link: http://lkml.kernel.org/r/1478077718-37424-3-git-send-email-xinhui.pan@linux.vnet.ibm.com [ Translated to English. ] Signed-off-by: Ingo Molnar --- kernel/locking/osq_lock.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) (limited to 'kernel/locking') diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c index 4ea2710b9d6c..a3167941093b 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 +123,10 @@ 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 avoid waiting for a preempted + * lock holder: */ - if (need_resched()) + if (need_resched() || vcpu_is_preempted(node_cpu(node->prev))) goto unqueue; cpu_relax(); -- cgit v1.2.3