Messages in this thread | | | Subject | Re: [PATCH 0/3] blk-mq & nvme: introduce .map_changed | From | Jens Axboe <> | Date | Tue, 29 Sep 2015 08:47:06 -0600 |
| |
On 09/29/2015 08:26 AM, Keith Busch wrote: > On Mon, 28 Sep 2015, Ming Lei wrote: >> This patchset introduces .map_changed callback into 'struct blk_mq_ops', >> and use this callback to get NVMe notified about the mapping changed >> event, >> then NVMe can update the irq affinity hint for its queues. > > I think this is going the wrong direction. Shouldn't we provide blk-mq > the vectors in the tag set so that layer can manage the irq hints? > > This could lead to more cpu-queue assignment optimizations from using > that information. For example, two h/w contexts sharing the same vector > shouldn't be assigned to cpus on different NUMA nodes.
I agree, this is moving in the wrong direction. Currently the sw <->hw queue mappings are in blk-mq, and this is the exact same information base we need for IRQ affinity handling. We need to move in the direction of having blk-mq helpers handle that part too, not pass notifications to the lower level driver to update its IRQ mappings.
>> Also the 'cpumask' in 'struct blk_mq_tags' isn't needed any more, so >> remove >> that and related kernel interface. > > It was added to the tags because the cpu mask is an artifact of the > tags rather that duplicating it across all the h/w contexts sharing the > same set. It also doesn't let a h/w context from one namespace overwrite > another's cpu affinity mask when they share the same vector.
So having the mask in the tags is really odd, it should be in some per-device type data instead.
-- Jens Axboe
| |