On Thu, Jan 14, 2016 at 09:15:13PM +0100, Peter Zijlstra wrote:

On Thu, Jan 14, 2016 at 11:42:02AM -0800, Leonid Yegoshin wrote:

quoted

An the only point - please use an appropriate SYNC_* barriers instead of
heavy bold hammer. That stuff was design explicitly to support the
requirements of Documentation/memory-barriers.txt

That's madness. That document changes from version to version as to what
we _think_ the actual hardware does. It is _NOT_ a specification.

There is work in progress on a specification, but please don't hold
your breath.  And I am not as optimistic as I might be about any formal
specification keeping up with the Linux kernel or with the hardware that
it supports.  But it seems worth a good try.

You cannot design hardware from that. Its incomplete and fails to
specify a bunch of things. It not a mathematically sound definition of a
memory model.

Please stop referring to that document for what a particular barrier
_should_ do.  Explain what MIPS does, so we can attempt to integrate
this knowledge with our knowledge of PPC/ARM/Alpha/x86/etc. and improve
upon our understanding of hardware and improve the Linux memory model.

Please!

							Thanx, Paul