On Sat, Jun 02 2007, Tejun Heo wrote: > Hello, > > Jens Axboe wrote: > >> Would that be very different from issuing barrier and not waiting for > >> its completion? For ATA and SCSI, we'll have to flush write back cache > >> anyway, so I don't see how we can get performance advantage by > >> implementing separate WRITE_ORDERED. I think zero-length barrier > >> (haven't looked at the code yet, still recovering from jet lag :-) can > >> serve as genuine barrier without the extra write tho. > > > > As always, it depends :-) > > > > If you are doing pure flush barriers, then there's no difference. Unless > > you only guarantee ordering wrt previously submitted requests, in which > > case you can eliminate the post flush. > > > > If you are doing ordered tags, then just setting the ordered bit is > > enough. That is different from the barrier in that we don't need a flush > > of FUA bit set. > > Hmmm... I'm feeling dense. Zero-length barrier also requires only one > flush to separate requests before and after it (haven't looked at the > code yet, will soon). Can you enlighten me? Yeah, that's what the zero-length barrier implementation I posted does. Not sure if you have a question beyond that, if so fire away :-) -- Jens Axboe -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
