On Wed, Feb 21 2007, Tejun Heo wrote: > [cc'ing Ric, Hannes and Dongjun, Hello. Feel free to drag other people in.] > > Robert Hancock wrote: > > Jens Axboe wrote: > >> But we can't really change that, since you need the cache flushed before > >> issuing the FUA write. I've been advocating for an ordered bit for > >> years, so that we could just do: > >> > >> 3. w/FUA+ORDERED > >> > >> normal operation -> barrier issued -> write barrier FUA+ORDERED > >> -> normal operation resumes > >> > >> So we don't have to serialize everything both at the block and device > >> level. I would have made FUA imply this already, but apparently it's not > >> what MS wanted FUA for, so... The current implementations take the FUA > >> bit (or WRITE FUA) as a hint to boost it to head of queue, so you are > >> almost certainly going to jump ahead of already queued writes. Which we > >> of course really do not. > > Yeah, I think if we have tagged write command and flush tagged (or > barrier tagged) things can be pretty efficient. Again, I'm much more > comfortable with separate opcodes for those rather than bits changing > the behavior. ORDERED+FUA NCQ would still be preferable to an NCQ enabled flush command, though. > Another idea Dongjun talked about while drinking in LSF was ranged > flush. Not as flexible/efficient as the previous option but much less > intrusive and should help quite a bit, I think. But that requires extensive tracking, I'm not so sure the implementation of that for barriers would be very clean. It'd probably be good for fsync, though. -- Jens Axboe - To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
