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SubjectRe: QUEUE_FLAG_CLUSTER: not working in 2.6.24 ?
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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