[RFC][PATCH] ring-buffer: Replace this_cpu_{read,write} with this_cpu_ptr()

On Tue, 17 Mar 2015 00:56:51 -0500 (CDT)
Christoph Lameter [off-list ref] wrote:

On Mon, 16 Mar 2015, Steven Rostedt wrote:

quoted

It has come to my attention that this_cpu_read/write are horrible on
architectures other than x86. Worse yet, they actually disable
preemption or interrupts! This caused some unexpected tracing results
on ARM.

Well its just been 7 years or so. Took a long time it seems.

The code that I added was not 7 years old. And not all people send me
reports like this.

These would need to be implemented on the architectures to
have comparable performance.

quoted

I may go and remove all this_cpu_read,write() calls from my code
because of this.

You could do that with __this_cpo_* but not this_cpu_*(). Doing
it to this_cpu_* would make the operations no longer per cpu atomic. If
they do not need per cpu atomicity then you could have used __this_cpu_*
instead. And  __this_cpu_* do not disable preemption or interrupts.

I do not need it to be atomic.

So please do not send patches based on gut reactions.

What else would you like me to do? It was an RFC, and it worked.

NAK

For this particular patch, I may override the NAK as I do not see a
downside for it. Why should x86 get an advantage at the expense of ARM?

-- Steve