----- On Feb 6, 2018, at 9:11 AM, Will Deacon will.deacon@xxxxxxx wrote: > On Tue, Feb 06, 2018 at 02:06:50PM +0000, Mathieu Desnoyers wrote: >> ----- On Feb 6, 2018, at 8:55 AM, Will Deacon will.deacon@xxxxxxx wrote: >> > On Tue, Feb 06, 2018 at 12:52:34PM +0000, Mathieu Desnoyers wrote: >> >> One approach I would consider for this is to duplicate this >> >> comment and add it just above the "eret" instruction within the >> >> macro: >> >> >> >> /* >> >> * ARCH_HAS_MEMBARRIER_SYNC_CORE rely on eret context synchronization >> >> * when returning from IPI handler, and when returning to user-space. >> >> */ >> >> >> >> Or perhaps Will has something else in mind ? >> > >> > To be honest with you, I'd just drop the comment entirely. entry.S is >> > terrifying these days and nobody should have to go in there to understand >> > why we select ARCH_HAS_MEMBARRIER_SYNC_CORE. If you really feel a justification >> > is needed, I'd be happy with a line in the Kconfig file. >> >> My concern is that someone wanting to optimize away a few cycles by changing >> eret to something else in the future will not be looking at Kconfig: that >> person will be staring at entry.S. > > That person will probably also be me, or somebody who sits within punching > distance. I really wouldn't worry about it. There a bunch of other > things that will break if we don't use ERET here and, if it's a real > concern, we're making the *huge* assumption that developers actually > read and pay attention to comments. > >> One alternative presented by PeterZ on irc is to do like ppc: define a >> macro for eret, and stick all appropriate comments near the macro. This >> way, it won't hurt when reading the code, but at least it keeps the >> comments near the instruction being discussed. > > For the sake of avoiding the conflict, can we just drop it for now, please? > Having an "eret" macro isn't obvious, because people won't realise that it's > a macro. Having "exception_return" is cryptic as hell to people familiar > with the ISA. I'd be OK not adding comments in the assembly provided that we document this within the new documentation file as I just posted as RFC: http://lkml.kernel.org/r/1517936413-19675-1-git-send-email-mathieu.desnoyers@xxxxxxxxxxxx Thoughts ? Thanks, Mathieu > > Will -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
