Messages in this thread | | | Date | Wed, 23 Feb 2011 11:10:43 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH RFC tip/core/rcu 11/11] rcu: move TREE_RCU from softirq to kthread |
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On Wed, Feb 23, 2011 at 11:34:32AM -0600, Christoph Lameter wrote: > On Wed, 23 Feb 2011, Mathieu Desnoyers wrote: > > > > > > + > > > > > + local_irq_save(flags); > > > > > + cpu = smp_processor_id(); > > Drop this line. > > > > > > + if (per_cpu(rcu_cpu_kthread_task, cpu) == NULL) { > > use this_cpu_read(rcu_cpu_kthread_task) > > > > > > + local_irq_restore(flags); > > > > > + return; > > > > > + } > > > > > + per_cpu(rcu_cpu_has_work, cpu) = 1; > > this_cpu_write(rcu_cpu_has_work, 1);
I have made these changes, thank you!
These do introduce redundant preempt_disable()/preempt_enable() calls, but this is not on a fastpath, so should be OK, and the improved readability is certainly nice. The read and the write do need to happen on the same CPU, FWIW.
> > This is not quite true on x86_64 and s390 anymore. __get_cpu_var() now > > uses a segment selector override to get the local CPU variable on x86. > > See x86's percpu.h for details. > > __get_cpu_var cannot use a segment override since there are places where > the address of the variable is taken. One needs to use this_cpu_ops for > that.
Thanks for the info!
Thanx, Paul
> > > True, but we could also argue that the multiple checks for being preempt > > > can also be an issue. > > > > At least on x86 preemption don't actually need to be disabled: selection > > of the right per-cpu memory location is done atomically with the rest of > > the instruction by the segment selector. > > Right.
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