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Date: Thu, 17 Apr 2014 11:21:06 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Christoph Lameter <cl@...ux.com> Cc: linux-kernel@...r.kernel.org, mingo@...nel.org, tj@...nel.org, grygorii.strashko@...com, peterz@...radead.org Subject: Re: How do I increment a per-CPU variable without warning? On Thu, Apr 17, 2014 at 12:53:28PM -0500, Christoph Lameter wrote: > On Thu, 17 Apr 2014, Paul E. McKenney wrote: > > > Fair enough! I resent the patch with your Ack to Tejun. > > Also note that you may want to use > > this_cpu_inc > > instead of raw_cpu_inc. > > this_cpu_inc will not disable preemption or anything on x86 but just > create a single instruction using instruction atomicity to avoid the > preempt on/off sequence. > > > On platforms that cannot emit such an instruction it will fallback to > disable interrupts for the sequence of instructions that increments the > value. > > With such an approach incrementing the counter should be much safer. If > the other arch want to avoid irq on/off sequences then they can override > the fallback to use atomics or whatever the processor architecture permits > to avoid the overhead of interrupt on / off. Fair enough, but in this case I don't need it to be safe. Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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