On Thu, Aug 05, 2010 at 05:11:56PM +0400, Vladislav Bolkhovitin wrote: > Chris Mason, on 08/02/2010 09:39 PM wrote: > >I regret putting the ordering into the original barrier code...it > >definitely did help reiserfs back in the day but it stinks of magic and > >voodoo. > > But if the ordering isn't in the common (block) code, how to > implement the "hardware offload" for ordering, i.e. ORDERED > commands, in an acceptable way? > > I believe, the decision was right, but the flags and magic requests > based interface (and, hence, implementation) was wrong. That's it > which stinks of magic and voodoo. The interface definitely has flaws. We didn't expand it because James popped up with a long list of error handling problems. Basically how do the hardware and the kernel deal with a failed request at the start of the chain. Somehow the easy way of failing them all turned out to be extremely difficult. Even if that part had been refined, I think trusting the ordering down to the lower layers was a doomed idea. The list of ways it could go wrong is much much longer (and harder to debug) than the list of benefits. With all of that said, I did go ahead and benchmark real ordered tags extensively on a scsi drive in the initial implementation. There was very little performance difference. -chris -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
