From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mark Lord Subject: Re: QUEUE_FLAG_CLUSTER: not working in 2.6.24 ? Date: Thu, 13 Dec 2007 14:59:35 -0500 Message-ID: <47618F27.6020906@rtr.ca> References: <47617B92.6020908@rtr.ca> <47617C07.3020501@rtr.ca> <47617E72.6080504@rtr.ca> <20071213185326.GQ26334@parisc-linux.org> <4761821F.3050602@rtr.ca> <20071213192633.GD10104@kernel.dk> <4761883A.7050908@rtr.ca> <476188C4.9030802@rtr.ca> <20071213193937.GG10104@kernel.dk> <47618B0B.8020203@rtr.ca> <20071213195350.GH10104@kernel.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20071213195350.GH10104@kernel.dk> Sender: linux-scsi-owner@vger.kernel.org To: Jens Axboe Cc: Mark Lord , Matthew Wilcox , IDE/ATA development list , Linux Kernel , linux-scsi List-Id: linux-ide@vger.kernel.org Jens Axboe wrote: > 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. .. I wonder if it's 9dfa52831e96194b8649613e3131baa2c109f7dc: "Merge blk_recount_segments into blk_recalc_rq_segments" ? That particular commit does some rather innocent code-shuffling, but also introduces a couple of new "if (nr_hw_segs == 1" conditions that were not there before. Okay git experts: how do I pull out a kernel at the point of this exact commit ? Thanks!