On Fri, 2009-08-14 at 18:19 -0600, Chris Worley wrote: > On Fri, Aug 14, 2009 at 5:45 PM, Matthew Wilcox<matthew@xxxxxx> wrote: > > On Fri, Aug 14, 2009 at 05:21:32PM -0600, Chris Worley wrote: > >> Sooner is better than waiting to coalesce. The longer an LBA is > >> inactive, the better for any management scheme. If you wait until > >> it's reused, you might as well forgo the advantages of TRIM/UNMAP. If > >> a the controller wants to coalesce, let it coalesce. > > > > I'm sorry, you're wrong. There is a tradeoff point, and it's different > > for each drive model. Sending down a steady stream of tiny TRIMs is > > going to give terrible performance. > > Sounds like you might be using junk for a device? > > For junk, a little coalescing may be warranted... like in the I/O > schedular, but no more than 100usecs wait before posting, or then you > effect high performing devices too. Um, I think you missed the original point in all of this at the beginning of the thread: On ATA TRIM commands cannot be tagged. This means you have to drain the outstanding NCQ commands (stalling the device) before you can send a TRIM. If we do this for every discard, the performance impact will be pretty devastating, hence the need to coalesce. It's nothing really to do with device characteristics, it's an ATA protocol problem. James -- 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
