Re: Another (ESP?) scsi blk-mq problem on sparc64

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On 11/24/2014 10:31 AM, Paul E. McKenney wrote:
On Mon, Nov 24, 2014 at 10:16:15AM -0700, Jens Axboe wrote:
On 11/24/2014 09:22 AM, Paul E. McKenney wrote:
On Mon, Nov 24, 2014 at 08:35:46AM -0700, Jens Axboe wrote:
On 11/24/2014 01:21 AM, Christoph Hellwig wrote:
On Fri, Nov 21, 2014 at 02:56:00PM -0500, David Miller wrote:
I would suggest looking into the possibility that we allocate the memory
using the count of valid cpus, rather than the largest cpu number.

That's a common error that runs into problems with discontiguous
cpu numbering like Sparc sometimes has.

Yes, that does look like the case.  Do you have a good trick on how
to allocate a map for the highest possible cpu number without first
iterating the cpu map?  I couldn't find something that looks like a
highest_possible_cpu() helper.

Honestly I think that num_posible_cpus() should return the max of
number of CPUs (weigt), and the highest numbered CPU. It's a pain in
the butt to handle this otherwise.

Hear, hear!!!  That would make my life easier, and would make this sort
of problem much less likely to occur!

How about this one?

Works for me!

Thanks! I'll add an appropriate comment and send it out for review.

(Just for the record, as far as I know, this doesn't matter for RCU,
which already uses nr_cpu_ids.)

Was that done after hitting something like this?

Meelis, can you check if it fixes your issue?


--
Jens Axboe

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