Messages in this thread | | | Date | Fri, 13 Jun 2014 08:07:29 -0600 | From | Jens Axboe <> | Subject | Re: [PATCH v7] NVMe: conversion to blk-mq |
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On 06/12/2014 06:06 PM, Keith Busch wrote: > When cancelling IOs, we have to check if the hwctx has a valid tags > for some reason. I have 32 cores in my system and as many queues, but
It's because unused queues are torn down, to save memory.
> blk-mq is only using half of those queues and freed the "tags" for the > rest after they'd been initialized without telling the driver. Why is > blk-mq not making utilizing all my queues?
You have 31 + 1 queues, so only 31 mappable queues. blk-mq symmetrically distributes these, so you should have a core + thread sibling on 16 queues. And yes, that leaves 15 idle hardware queues for this specific case. I like the symmetry, it makes it more predictable if things are spread out evenly.
But it is a policy decision that could be changed. The logic is in the 50 lines of code in block/blk-mq-cpumap.c:blk_mq_update_queue_map().
Thanks for the abort and completion fixes, looks a lot better now. It might be cleaner to have blk_mq_tag_busy_iter() just work for !hctx->tags, since this is actually the 2nd time I've run into this now.
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