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SubjectRe: Upstream kernel fails to run on qemu-sparc64 due to commit 889fa31f0 (blk-mq: reduce unnecessary software queue looping)
On 04/17/2015 07:32 AM, Guenter Roeck wrote:
> On Thu, Apr 16, 2015 at 11:32:20PM -0700, Guenter Roeck wrote:
>> Hi,
>> my qemu-sparc64 tests fail to run with kernel v4.0-7245-ga39ef1a7c609.
>> Bisect points to commit 889fa31f00b ("blk-mq: reduce unnecessary software
>> queue looping"). Reverting this commit fixes the problem.
>> I had a look into the commit, but I have no idea what might be wrong.
>> I made the bisect log, images, configuration file, root file system, and directions
>> on how to run the images available at
>> Please let me know if there is any other information I can provide.
> As additional information:
> + * Set the map size to the number of mapped software queues.
> + * This is more accurate and more efficient than looping
> + * over all possibly mapped software queues.
> + */
> + map->map_size = hctx->nr_ctx / map->bits_per_word;
> On my system, hctx->nr_ctx is 1, and map->bits_per_word is 8.
> Thus map->map_size is set to 0, which doesn't make much sense.

> The system comes up if I replace the above code with
> map->map_size = DIV_ROUND_UP(hctx->nr_ctx, map->bits_per_word);
> I have no idea if that is the correct fix, though.

Ugh, yes indeed, looks like the <= was lost from a previous patch. Now I
wonder why it I didn't see any hangs with this... Thanks for reporting,
I'll get a fix in today.

Jens Axboe

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