Messages in this thread | | | Date | Thu, 13 Dec 2007 14:42:03 -0500 | From | Mark Lord <> | Subject | Re: QUEUE_FLAG_CLUSTER: not working in 2.6.24 ? |
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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".
But I will dig a bit more and see if I can find the culprit.
Cheers
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