On Wed, Oct 31, 2018 at 03:57:21PM -0700, Andy Lutomirski wrote:

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On Oct 31, 2018, at 2:00 PM, Peter Zijlstra [off-list ref] wrote:

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On Wed, Oct 31, 2018 at 01:36:48PM -0700, Andy Lutomirski wrote:

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This stuff is called *rare* write for a reason. Do we really want to
allow atomics beyond just store-release?  Taking a big lock and then
writing in the right order should cover everything, no?

Ah, so no. That naming is very misleading.

We modify page-tables a _lot_. The point is that only a few sanctioned
sites are allowed writing to it, not everybody.

I _think_ the use-case for atomics is updating the reference counts of
objects that are in this write-rare domain. But I'm not entirely clear
on that myself either. I just really want to avoid duplicating that
stuff.

Sounds nuts. Doing a rare-write is many hundreds of cycles at best.

Yes, which is why I'm somewhat sceptical of the whole endeavour.