| Message ID | 20170713161020.GA10325@bogon.didichuxing.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 07/13/2017 10:10 AM, weiping zhang wrote:
> one hw queue only has one hctx, reduce it's number same as nr_hw_queues.
What happens if a device registers with eg 4 hw queues, then later
calls blk_mq_update_nr_hw_queues()?
On Thu, Jul 13, 2017 at 10:14:31AM -0600, Jens Axboe wrote: > On 07/13/2017 10:10 AM, weiping zhang wrote: > > one hw queue only has one hctx, reduce it's number same as nr_hw_queues. > > What happens if a device registers with eg 4 hw queues, then later > calls blk_mq_update_nr_hw_queues()? > your means, 10 cpu, and device has 10 hw queues, but only register 4, and then update it to 10, no place store new hctx. Am i understanding right ? if yes, could you tell me why driver do that ? thanks. -- weiping
On 07/13/2017 10:30 AM, weiping zhang wrote: > On Thu, Jul 13, 2017 at 10:14:31AM -0600, Jens Axboe wrote: >> On 07/13/2017 10:10 AM, weiping zhang wrote: >>> one hw queue only has one hctx, reduce it's number same as nr_hw_queues. >> >> What happens if a device registers with eg 4 hw queues, then later >> calls blk_mq_update_nr_hw_queues()? >> > > your means, 10 cpu, and device has 10 hw queues, but only register 4, > and then update it to 10, no place store new hctx. Am i understanding > right ? if yes, could you tell me why driver do that ? thanks. It doesn't matter why the driver would do that, the fact is that this is a feature we support and it's a part of the API. NBD uses it, for instance. Your patch breaks it, for saving a bit of memory. So I will not include it.
diff --git a/block/blk-mq.c b/block/blk-mq.c index 05dfa3f..8c98f59 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2320,8 +2320,8 @@ struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set, /* init q->mq_kobj and sw queues' kobjects */ blk_mq_sysfs_init(q); - q->queue_hw_ctx = kzalloc_node(nr_cpu_ids * sizeof(*(q->queue_hw_ctx)), - GFP_KERNEL, set->numa_node); + q->queue_hw_ctx = kzalloc_node(set->nr_hw_queues * + sizeof(*(q->queue_hw_ctx)),GFP_KERNEL, set->numa_node); if (!q->queue_hw_ctx) goto err_percpu;
one hw queue only has one hctx, reduce it's number same as nr_hw_queues. Signed-off-by: weiping zhang <zhangweiping@didichuxing.com> --- block/blk-mq.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)