diff options
author | Jeremy Fitzhardinge <jeremy@goop.org> | 2013-08-09 14:21:49 (GMT) |
---|---|---|
committer | H. Peter Anvin <hpa@linux.intel.com> | 2013-08-09 14:53:05 (GMT) |
commit | 545ac13892ab391049a92108cf59a0d05de7e28c (patch) | |
tree | e993b90bcbedd44b77c895cf7fcee89ee5fe9d51 /arch/x86/xen/spinlock.c | |
parent | c095ba7224d8edc71dcef0d655911399a8bd4a3f (diff) | |
download | linux-545ac13892ab391049a92108cf59a0d05de7e28c.tar.xz |
x86, spinlock: Replace pv spinlocks with pv ticketlocks
Rather than outright replacing the entire spinlock implementation in
order to paravirtualize it, keep the ticket lock implementation but add
a couple of pvops hooks on the slow patch (long spin on lock, unlocking
a contended lock).
Ticket locks have a number of nice properties, but they also have some
surprising behaviours in virtual environments. They enforce a strict
FIFO ordering on cpus trying to take a lock; however, if the hypervisor
scheduler does not schedule the cpus in the correct order, the system can
waste a huge amount of time spinning until the next cpu can take the lock.
(See Thomas Friebel's talk "Prevent Guests from Spinning Around"
http://www.xen.org/files/xensummitboston08/LHP.pdf for more details.)
To address this, we add two hooks:
- __ticket_spin_lock which is called after the cpu has been
spinning on the lock for a significant number of iterations but has
failed to take the lock (presumably because the cpu holding the lock
has been descheduled). The lock_spinning pvop is expected to block
the cpu until it has been kicked by the current lock holder.
- __ticket_spin_unlock, which on releasing a contended lock
(there are more cpus with tail tickets), it looks to see if the next
cpu is blocked and wakes it if so.
When compiled with CONFIG_PARAVIRT_SPINLOCKS disabled, a set of stub
functions causes all the extra code to go away.
Results:
=======
setup: 32 core machine with 32 vcpu KVM guest (HT off) with 8GB RAM
base = 3.11-rc
patched = base + pvspinlock V12
+-----------------+----------------+--------+
dbench (Throughput in MB/sec. Higher is better)
+-----------------+----------------+--------+
| base (stdev %)|patched(stdev%) | %gain |
+-----------------+----------------+--------+
| 15035.3 (0.3) |15150.0 (0.6) | 0.8 |
| 1470.0 (2.2) | 1713.7 (1.9) | 16.6 |
| 848.6 (4.3) | 967.8 (4.3) | 14.0 |
| 652.9 (3.5) | 685.3 (3.7) | 5.0 |
+-----------------+----------------+--------+
pvspinlock shows benefits for overcommit ratio > 1 for PLE enabled cases,
and undercommits results are flat
Signed-off-by: Jeremy Fitzhardinge <jeremy@goop.org>
Link: http://lkml.kernel.org/r/1376058122-8248-2-git-send-email-raghavendra.kt@linux.vnet.ibm.com
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Tested-by: Attilio Rao <attilio.rao@citrix.com>
[ Raghavendra: Changed SPIN_THRESHOLD, fixed redefinition of arch_spinlock_t]
Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Diffstat (limited to 'arch/x86/xen/spinlock.c')
-rw-r--r-- | arch/x86/xen/spinlock.c | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c index cf3caee..d509629 100644 --- a/arch/x86/xen/spinlock.c +++ b/arch/x86/xen/spinlock.c @@ -139,6 +139,9 @@ struct xen_spinlock { xen_spinners_t spinners; /* count of waiting cpus */ }; +static DEFINE_PER_CPU(int, lock_kicker_irq) = -1; + +#if 0 static int xen_spin_is_locked(struct arch_spinlock *lock) { struct xen_spinlock *xl = (struct xen_spinlock *)lock; @@ -167,7 +170,6 @@ static int xen_spin_trylock(struct arch_spinlock *lock) } static DEFINE_PER_CPU(char *, irq_name); -static DEFINE_PER_CPU(int, lock_kicker_irq) = -1; static DEFINE_PER_CPU(struct xen_spinlock *, lock_spinners); /* @@ -354,6 +356,7 @@ static void xen_spin_unlock(struct arch_spinlock *lock) if (unlikely(xl->spinners)) xen_spin_unlock_slow(xl); } +#endif static irqreturn_t dummy_handler(int irq, void *dev_id) { @@ -418,13 +421,14 @@ void __init xen_init_spinlocks(void) return; BUILD_BUG_ON(sizeof(struct xen_spinlock) > sizeof(arch_spinlock_t)); - +#if 0 pv_lock_ops.spin_is_locked = xen_spin_is_locked; pv_lock_ops.spin_is_contended = xen_spin_is_contended; pv_lock_ops.spin_lock = xen_spin_lock; pv_lock_ops.spin_lock_flags = xen_spin_lock_flags; pv_lock_ops.spin_trylock = xen_spin_trylock; pv_lock_ops.spin_unlock = xen_spin_unlock; +#endif } #ifdef CONFIG_XEN_DEBUG_FS |