----- On Oct 5, 2015, at 7:21 PM, Rusty Russell rusty@xxxxxxxxxx wrote: > Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> writes: >> Hi Andrew, >> >> Here is a repost of sys_membarrier, rebased on top of Linus commit >> c4b5fd3fb2058b650447372472ad24e2a989f9f6 without any change since the >> last v19 post other that proceeding to further testing. When merging >> with other system calls, system call number conflicts should be quite >> straightforward to handle, there is nothing special there. > > Hi Mathieu, > > Great to see this go in! One small note: it talks about > threads, but membarrier as currently implemented would cover any shared > memory. If you plan to optimize in future, that might not be the case: > we'd want an address argument for those cases? Hi Rusty, Indeed, the current membarrier implementation only supports the MEMBARRIER_CMD_SHARED flag, which works even with shared memory across processes. If we ever want to optimize that for single-process, multi-threaded cases, we would have to add a new flag (e.g. MEMBARRIER_CMD_PRIVATE). This is quite similar to what already exists in the futex system call. I'm not sure I fully understand where the address argument you are describing would be useful. So far, I see two main use-cases: we either interact with memory that is local to a single process, or with memory shared across processes. We could indeed think about sending a membarrier to all processes using a specific shared memory area (hence the possible need for an address argument). This could eventually be supported by adding a specific flag for this (e.g. MEMBARRIER_CMD_SHM), which would indicate that an extra parameter is provided (an address). Thoughts ? Thanks for the feedback! Mathieu > > Cheers, > Rusty. -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
