Messages in this thread |  | | | Date | Wed, 13 Jan 2010 11:42:00 -0800 | | From | David Daney <> | | Subject | Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory barrier (v5) |
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Mathieu Desnoyers wrote: > * Nicholas Miell (nmiell@comcast.net) wrote: >> On Wed, 2010-01-13 at 13:24 -0500, Mathieu Desnoyers wrote: >>> * Nicholas Miell (nmiell@comcast.net) wrote: >>> >>>> The whole point of compat and incompat flags is that it allows new >>>> applications to run on old kernels and either work or fail as >>>> appropriate, depending on whether the new features they're using must be >>>> implemented or can be silently ignored. >>> I see. Thanks for the explanation. Then the expedited flag should >>> clearly be part of the mandatory flags. >>> >>> Can you point me to other system calls that are doing this ? >>> >>> Thanks, >>> >>> Mathieu >> Not off the top of my head, but I did steal the idea from the ext2/3/4 >> disk format. > > Sounds a bit over-engineered to me for system calls, but who knows if we > eventually have to extend sys_membarrier(). This involves that, right > now, I'd have to add a header to include/linux to define these flags. > Also, "int expedited" is a bit clearer, but less flexible, than "int > flags". Anyone else have comments about this ? >
It doesn't bother me that you have to do extra work to add the flag definitions to a header file. :-)
As I understand it, the proposal is to have the option to extend the ABI based on as yet undefined flag bits. This doesn't seem like a bad thing.
The runtime overhead of testing a single bit vs. non-zero in the parameter shouldn't be an issue.
David Daney
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