----- Original Message ----- > On Tue, Mar 17, 2015 at 10:57:50AM -0700, [email protected] wrote: > > On Tue, Mar 17, 2015 at 06:30:35PM +0100, Peter Zijlstra wrote: > > > On Tue, Mar 17, 2015 at 01:22:02PM -0400, Mathieu Desnoyers wrote: > > > > Here is an implementation of a new system call, sys_membarrier(), which > > > > executes a memory barrier on either all running threads of the current > > > > process (MEMBARRIER_PRIVATE) issues a memory barrier on all threads > > > > running on the system (~MEMBARRIER_PRIVATE). Both are currently > > > > implemented by calling synchronize_sched(). > > > > > > Then why bother with the flag? > > > > Semantically, MEMBARRIER_PRIVATE is allowed to avoid issuing a barrier > > on CPUs not running the current process if it can, while > > ~MEMBARRIER_PRIVATE may not. (The latter would be useful for > > applications such as system-wide tracing.) That they're currently both > > implemented the same way doesn't mean they're semantically equivalent. > > Sure; but why bother with pointless fluff like that? We can always > introduce the private flag if and when it starts to make sense having > it.
Without the expedited implementation, the only usefulness of the private flag is to skip synchronize_sched() if called from a single-threaded process. We could easily argue that if a process is using sys_membarrier in the first place, it's very likely that it is multithreaded. So I agree that we can drop the flag for now, and add it later on, e.g. when adding the expedited mode. I am tempted to leave the "flags" argument in place though, along with the "MEMBARRIER_QUERY" flag. Thoughts ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
