Re: the >1Tb block issue

[Michael Tokarev <mjt@tls.msk.ru>]

18.05.2010 22:38, Michael Tokarev пишет:
> 18.05.2010 22:09, Avi Kivity wrote:
>> On 05/18/2010 09:03 PM, Michael Tokarev wrote:
>>> 18.05.2010 21:38, Avi Kivity wrote:
>>>
>>>>> [Qemu-devel] [PATCH +stable] block: don't attempt to merge overlapping
>>>>> requests
>>>>>
>>>>> quick tests shows it works correctly so far.
>>>>> At least it went further than before, not
>>>>> stopping at the "usual" sector 3145727872.
>>>>>
>>>>> Hmm. Ide has no queue, hence no mergeing,
>>>>> that's why it does not occur with ide,
>>>>> right? :)
>>>>
> []
>>>> Yes. Why would Linux post overlapping requests? makes
>>>> 0xffffffff00000000
>>>> sense.
> []
>>> Note also that it's not as on the original bugreport -
>>> there, the sector# is apparently different:
>>> http://sourceforge.net/tracker/?func=detail&aid=2933400&group_id=180599&atid=893831
>>>
>>
>> I don't think it's related to a particular sector number.
>
> I added a debug printf into the place that is touched
> by the patch mentioned above, to print the case where
> the request were merged before that patch but not any
> more with it applied:
>
> if (reqs[i].sector == oldreq_last) {
> merge = 1;
> }
> else if (reqs[i].sector < oldreq_last)
> fprintf(stderr, "NOT mergeing:\n"
> " reqs[i].sector=%Ld oldreq_last=%Ld\n"
> " reqs[outidx].sector=%Ld reqs[outidx].nb_sectors=%d\n"
> , reqs[i].sector, oldreq_last,
> reqs[outidx].sector, reqs[outidx].nb_sectors);
>
> In a few runs it showed different info (and I modified the
> printf line 2 times too):
>
> NOT mergeing: reqs[i].sector=92306456 oldreq_last=3145728000
> NOT mergeing:
> reqs[i].sector=92322056 oldreq_last=3145728000
> reqs[outidx].sector=3145727872
> NOT mergeing:
> reqs[i].sector=0 oldreq_last=3145728000
> reqs[outidx].sector=3145727872 reqs[outidx].nb_sectors=128
> NOT mergeing:
> reqs[i].sector=0 oldreq_last=3145728000
> reqs[outidx].sector=3145727872 reqs[outidx].nb_sectors=128
> NOT mergeing:
> reqs[i].sector=92308152 oldreq_last=3145728000
> reqs[outidx].sector=3145727872 reqs[outidx].nb_sectors=128
> NOT mergeing:
> reqs[i].sector=0 oldreq_last=3145728000
> reqs[outidx].sector=3145727872 reqs[outidx].nb_sectors=128

> So it's definitely timing-related somehow (esp. it changes
> when interrupting mkfs and immediately starting again), and
> shows different values, but for me it's - apparently - always
> reqs[outidx].sector=3145727872 together with some other sector.

And once I hit "Send" it showed another:

NOT mergeing:
  reqs[i].sector=760 oldreq_last=3141599488
  reqs[outidx].sector=3141597896 reqs[outidx].nb_sectors=1592

so it's not the case here ;)

> /mjt