Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> writes: > ----- 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). That's exactly what I was thinking; eg. it can be optimized in the case where nothing else with the memory mapped is running. Cheers, Rusty. -- 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
