Messages in this thread | | | Date | Tue, 6 Mar 2012 08:46:01 +0100 | From | Ingo Molnar <> | Subject | Re: [patch 5/8] x86: use this_cpu_xxx to replace percpu_xxx funcs |
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* akpm@linux-foundation.org <akpm@linux-foundation.org> wrote:
> From: Alex Shi <alex.shi@intel.com> > Subject: x86: use this_cpu_xxx to replace percpu_xxx funcs > > Since percpu_xxx() serial functions are duplicate with this_cpu_xxx(). > Removing percpu_xxx() definition and replacing them by this_cpu_xxx() in > code. > > And further more, as Christoph Lameter's requirement, I try to use > __this_cpu_xx to replace this_cpu_xxx if it is in preempt safe scenario. > The preempt safe scenarios include: > 1, in irq/softirq/nmi handler > 2, protected by preempt_disable > 3, protected by spin_lock > 4, if the code context imply that it is preempt safe, like the code is > follows or be followed a preempt safe code. > > BTW, In fact, this_cpu_xxx are same as __this_cpu_xxx since all funcs > implement in a single instruction for x86 machine. But it maybe other > platforms' performance.
but this is an x86 only patch.
> - percpu_write(irq_regs, new_regs); > + __this_cpu_write(irq_regs, new_regs);
So what's the point of all this ugly churn?
Will percpu_write() be removed altogether? If so then the changelog should say *that*, and explain that on x86 this is a simple renaming of the API, not a long explanation about scenarios that don't actually matter.
If percpu_write() is not being removed then I don't see how this patch is an improvement: it's supposed to result in the same instructions being emitted, and __this_cpu_write() et al are distinctly longer to write ...
So what's the plan here?
Thanks,
Ingo
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