Messages in this thread | ![/](/images/icornerl.gif) | | Date | Thu, 15 Jan 2015 21:27:14 -0600 (CST) | From | Christoph Lameter <> | Subject | Re: [PATCH v2 1/2] mm/slub: optimize alloc/free fastpath by removing preemption on/off |
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On Thu, 15 Jan 2015, Steven Rostedt wrote:
> profiling function tracing I discovered that accessing preempt_count > was actually quite expensive, even just to read. But it may not be as > bad since Peter Zijlstra converted preempt_count to a per_cpu variable. > Although, IIRC, the perf profiling showed the access to the %gs > register was where the time consuming was happening, which is what > I believe per_cpu variables still use.
The %gs register is not used since the address of the per cpu area is available as one of the first fields in the per cpu areas.
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