Re: [PATCH for 4.16 04/10] membarrier: provide SHARED_EXPEDITED command (v2)

On Tue, 16 Jan 2018, Mathieu Desnoyers wrote:

----- On Jan 16, 2018, at 1:20 PM, Thomas Gleixner tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org wrote:

quoted

And I really have to ask whether this should be named _GLOBAL_ instead of
_SHARED_.

Hmm?

I agree with you that this behavior fits better a "global" definition
than a "shared" one, especially given that it does not target a specific
shared memory mapping. The main issue I have is due to the pre-existing
MEMBARRIER_CMD_SHARED introduced in Linux 4.3. That one should also have
been called "MEMBARRIER_CMD_GLOBAL" based on the current line of thoughts.

Do you envision a way to transition forward to a new "MEMBARRIER_CMD_GLOBAL" for
the currently existing MEMBARRIER_CMD_SHARED ?

Perhaps with a duplicated enum entry ?

enum membarrier_cmd {
        MEMBARRIER_CMD_QUERY                                    = 0,
        MEMBARRIER_CMD_SHARED                                   = (1 << 0), /* use MEMBARRIER_CMD_GLOBAL instead */
        MEMBARRIER_CMD_GLOBAL                                   = (1 << 0),

That should work. Though I doubt that you ever can get rid of CMD_SHARED,
but at least the code is clearer that way.

Thanks,

	tglx