On Thu, Dec 13 2007, 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 would be the sg chain stuff, I don't think there's any correlation between the two "bugs" (ie I don't get how you jump to the conclusion that this regression is from stuff before that). Just go back as early as you can, you could even just start with a -rc bisect. -- 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
