Messages in this thread Patches in this message | | | Date | Tue, 24 May 2011 14:23:45 -0700 | From | Yinghai Lu <> | Subject | Re: [tip:core/rcu] Revert "rcu: Decrease memory-barrier usage based on semi-formal proof" |
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On 05/23/2011 06:35 PM, Paul E. McKenney wrote: > On Mon, May 23, 2011 at 06:26:23PM -0700, Yinghai Lu wrote: >> On 05/23/2011 06:18 PM, Paul E. McKenney wrote: >> >>> OK, so it looks like I need to get this out of the way in order to track >>> down the delays. Or does reverting PeterZ's patch get you a stable >>> system, but with the longish delays in memory_dev_init()? If the latter, >>> it might be more productive to handle the two problems separately. >>> >>> For whatever it is worth, I do see about 5% increase in grace-period >>> duration when switching to kthreads. This is acceptable -- your >>> 30x increase clearly is completely unacceptable and must be fixed. >>> Other than that, the main thing that affects grace period duration is >>> the setting of CONFIG_HZ -- the smaller the HZ value, the longer the >>> grace-period duration. >> >> for my 1024g system when memory hotadd is enabled in kernel config: >> 1. current linus tree + tip tree: memory_dev_init will take about 100s. >> 2. current linus tree + tip tree + your tree - Peterz patch: >> a. on fedora 14 gcc: will cost about 4s: like old times >> b. on opensuse 11.3 gcc: will cost about 10s. > > So some patch in my tree that is not yet in tip makes things better? > > If so, could you please see which one? Maybe that would give me a hint > that could make things better on opensuse 11.3 as well.
today's tip:
[ 31.795597] cpu_dev_init done [ 40.930202] memory_dev_init done
after
commit e219b351fc90c0f5304e16efbc603b3b78843ea1 Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Date: Mon May 16 02:44:06 2011 -0700
rcu: Remove old memory barriers from rcu_process_callbacks()
Second step of partitioning of commit e59fb3120b.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 3731141..011bf6f 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1460,25 +1460,11 @@ __rcu_process_callbacks(struct rcu_state *rsp, struct rcu_data *rdp) */ static void rcu_process_callbacks(void) { - /* - * Memory references from any prior RCU read-side critical sections - * executed by the interrupted code must be seen before any RCU - * grace-period manipulations below. - */ - smp_mb(); /* See above block comment. */ - __rcu_process_callbacks(&rcu_sched_state, &__get_cpu_var(rcu_sched_data)); __rcu_process_callbacks(&rcu_bh_state, &__get_cpu_var(rcu_bh_data)); rcu_preempt_process_callbacks(); - /* - * Memory references from any later RCU read-side critical sections - * executed by the interrupted code must be seen after any RCU - * grace-period manipulations above. - */ - smp_mb(); /* See above block comment. */ - /* If we are last CPU on way to dyntick-idle mode, accelerate it. */ rcu_needs_cpu_flush(); } cause
[ 32.235103] cpu_dev_init done [ 74.897943] memory_dev_init done
then add
commit d0d642680d4cf5cc2ccf542b74a3c8b7e197306b Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Date: Mon May 16 02:52:04 2011 -0700
rcu: Don't do reschedule unless in irq
Condition the set_need_resched() in rcu_irq_exit() on in_irq(). This should be a no-op, because rcu_irq_exit() should only be called from irq.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 011bf6f..195b3a3 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -421,8 +421,9 @@ void rcu_irq_exit(void) WARN_ON_ONCE(rdtp->dynticks & 0x1); /* If the interrupt queued a callback, get out of dyntick mode. */ - if (__this_cpu_read(rcu_sched_data.nxtlist) || - __this_cpu_read(rcu_bh_data.nxtlist)) + if (in_irq() && + (__this_cpu_read(rcu_sched_data.nxtlist) || + __this_cpu_read(rcu_bh_data.nxtlist))) set_need_resched(); } got: [ 34.384490] cpu_dev_init done [ 86.656322] memory_dev_init done
after
commit fcfc28801f5b3b9c70616fc57e3a2c6f52014e14 Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Date: Mon May 16 14:27:31 2011 -0700
rcu: Make rcu_enter_nohz() pay attention to nesting
The old version of rcu_enter_nohz() forced RCU into nohz mode even if the nesting count was non-zero. This change causes rcu_enter_nohz() to hold off for non-zero nesting counts.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 195b3a3..99c6038 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -324,8 +324,8 @@ void rcu_enter_nohz(void) smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */ local_irq_save(flags); rdtp = &__get_cpu_var(rcu_dynticks); - rdtp->dynticks++; - rdtp->dynticks_nesting--; + if (--rdtp->dynticks_nesting == 0) + rdtp->dynticks++; WARN_ON_ONCE(rdtp->dynticks & 0x1); local_irq_restore(flags); } got:
[ 32.414049] cpu_dev_init done [ 38.237979] memory_dev_init done
after: commit bcd6e68330f893a81b3519ab3c5fc2bebbc9988c Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Date: Tue Sep 7 10:38:22 2010 -0700
rcu: Decrease memory-barrier usage based on semi-formal proof ...
got:
[ 32.447936] cpu_dev_init done [ 111.027066] memory_dev_init done
after
commit fbb753fb9dd62318d27fa070c686423ced139817 Author: Paul E. McKenney <paul.mckenney@linaro.org> Date: Wed May 11 05:33:33 2011 -0700
atomic: Add atomic_or()
An atomic_or() function is needed by TREE_RCU to avoid deadlock, so add a generic version.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/include/linux/atomic.h b/include/linux/atomic.h index 96c038e..ee456c7 100644 --- a/include/linux/atomic.h +++ b/include/linux/atomic.h @@ -34,4 +34,17 @@ static inline int atomic_inc_not_zero_hint(atomic_t *v, int hint) } #endif +#ifndef CONFIG_ARCH_HAS_ATOMIC_OR +static inline void atomic_or(int i, atomic_t *v) +{ + int old; + int new; + + do { + old = atomic_read(v); + new = old | i; + } while (atomic_cmpxchg(v, old, new) != old); +} +#endif /* #ifndef CONFIG_ARCH_HAS_ATOMIC_OR */ + #endif /* _LINUX_ATOMIC_H */ got:
[ 32.803704] cpu_dev_init done [ 99.171292] memory_dev_init done
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