On Mon, 2008-11-24 at 18:52 +0000, David Woodhouse wrote: > On Mon, 2008-11-24 at 13:42 -0500, James Bottomley wrote: > > On Mon, 2008-11-24 at 09:03 +0000, David Woodhouse wrote: > > > On Mon, 2008-11-24 at 07:52 +0900, James Bottomley wrote: > > > > On Sun, 2008-11-23 at 13:39 +0000, David Woodhouse wrote: > > > > > > We don't attempt to put non-contiguous ranges into a single TRIM yet. > > > > > > > > > > We don't even merge contiguous ranges -- I still need to fix the > > > > > elevators to stop writes crossing writes, > > > > > > > > I don't think we want to do that ... it's legal if the write isn't a > > > > barrier and it will inhibit merging. That may be just fine for a SSD, > > > > but it's not for spinning media since they get better performance out of > > > > merged writes. > > > > > > No, I just mean writes _to the same sector_. At the moment, we happily > > > let those cross each other in the queue. > ... > > It's not a bug ... but changing it might be feasible ... as long as it > > doesn't affect write performance too much (which I don't think it will), > > since it is in the critical path. > > We could argue about how much sense it makes to let two writes to the > same sector actually happen in reverse order. > > Especially given the fact that we actually _do_ preserve ordering in > some cases; just not in others. (We preserve ordering only if the start > and end of the duplicate writes are _precisely_ matching; if it's just > overlapping (which may well happen in the presence of merges), then this > check doesn't trigger. > > But that's just semantics. Yes, changing it should be feasible. I talked > to Jens about that at the kernel summit, and we agreed that it should > probably be done. > > > > And _then_ we can think about special cases which let us merge > > > non-contiguous discards. > > > > I still think that treating discards as a special command from the > > outset is the better way forwards. > > They're already treated as a special command and you can special-case > them wherever you like, so I'm not entirely sure what you're suggesting. I mean that since it's not a bug, you don't have to do it for every write, just between a write and a discard, thus special casing the overlap checking code. James -- 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
