On Thu, Dec 13 2007, Mark Lord wrote: > Jens Axboe wrote: > >On Thu, Dec 13 2007, Mark Lord wrote: > >>Mark Lord wrote: > >>>Jens Axboe wrote: > >>>>On Thu, Dec 13 2007, Mark Lord wrote: > >>>>>Matthew Wilcox wrote: > >>>>>>On Thu, Dec 13, 2007 at 01:48:18PM -0500, Mark Lord wrote: > >>>>>>>Problem confirmed. 2.6.23.8 regularly generates segments up to > >>>>>>>64KB for libata, > >>>>>>>but 2.6.24 uses only 4KB segments and a *few* 8KB segments. > >>>>>>Just a suspicion ... could this be slab vs slub? ie check your > >>>>>>configs > >>>>>>are the same / similar between the two kernels. > >>>>>.. > >>>>> > >>>>>Mmmm.. a good thought, that one. > >>>>>But I just rechecked, and both have CONFIG_SLAB=y > >>>>> > >>>>>My guess is that something got changed around when Jens > >>>>>reworked the block layer for 2.6.24. > >>>>>I'm going to dig around in there now. > >>>>I didn't rework the block layer for 2.6.24 :-). The core block layer > >>>>changes since 2.6.23 are: > >>>> > >>>>- Support for empty barriers. Not a likely candidate. > >>>>- Shared tag queue fixes. Totally unlikely. > >>>>- sg chaining support. Not likely. > >>>>- The bio changes from Neil. Of the bunch, the most likely suspects in > >>>> this area, since it changes some of the code involved with merges and > >>>> blk_rq_map_sg(). > >>>>- Lots of simple stuff, again very unlikely. > >>>> > >>>>Anyway, it sounds odd for this to be a block layer problem if you do see > >>>>occasional segments being merged. So it sounds more like the input data > >>>>having changed. > >>>> > >>>>Why not just bisect it? > >>>.. > >>> > >>>Because the early 2.6.24 series failed to boot on this machine > >>>due to bugs in the block layer -- so the code that caused this regression > >>>is probably in the stuff from before the kernels became usable here. > >>.. > >> > >>That sounds more harsh than intended --> the earlier 2.6.24 kernels (up to > >>the first couple of -rc* ones failed here because of incompatibilities > >>between the block/bio changes and libata. > >> > >>That's better, I think! > > > >No worries, I didn't pick it up as harsh just as an odd conclusion :-) > > > >If I were you, I'd just start from the first -rc that booted for you. If > >THAT has the bug, then we'll think of something else. If you don't get > >anywhere, I can run some tests tomorrow and see if I can reproduce it > >here. > .. > > I believe that *anyone* can reproduce it, since it's broken long before > the requests ever get to SCSI or libata. Which also means that *anyone* > who wants to can bisect it, as well. > > I don't do "bisects". It was just a suggestion on how to narrow it down, do as you see fit. > But I will dig a bit more and see if I can find the culprit. Sure, I'll dig around as well. -- 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
