On Sun, Apr 07, 2019 at 06:55:20AM -0700, Dongli Zhang wrote: > [PATCH 1/1] blk-mq: do not splice ctx->rq_lists[type] to hctx->dispatch if ctx > is not mapped to hctx > > When a cpu is offline, blk_mq_hctx_notify_dead() is called once for each > hctx for the offline cpu. > > While blk_mq_hctx_notify_dead() is used to splice all ctx->rq_lists[type] > to hctx->dispatch, it never checks whether the ctx is already mapped to the > hctx. > > For example, on a VM (with nvme) of 4 cpu, to offline cpu 2 out of the > 4 cpu (0-3), blk_mq_hctx_notify_dead() is called once for each io queue > hctx: > > 1st: blk_mq_ctx->cpu = 2 for blk_mq_hw_ctx->queue_num = 3 > 2nd: blk_mq_ctx->cpu = 2 for blk_mq_hw_ctx->queue_num = 2 > 3rd: blk_mq_ctx->cpu = 2 for blk_mq_hw_ctx->queue_num = 1 > 4th: blk_mq_ctx->cpu = 2 for blk_mq_hw_ctx->queue_num = 0 > > Although blk_mq_ctx->cpu = 2 is only mapped to blk_mq_hw_ctx->queue_num = 2 > in this case, its ctx->rq_lists[type] will however be moved to > blk_mq_hw_ctx->queue_num = 3 during the 1st call of > blk_mq_hctx_notify_dead(). > > This patch would return and go ahead to next call of > blk_mq_hctx_notify_dead() if ctx is not mapped to hctx. Ha, I think you're right. It would be a bit more work, but it might be best if we could avoid calling the notify for each hctx that doesn't apply to the CPU. We might get that by registering a single callback for the request_queue and loop only the affected hctx's. But this patch looks good to me too. Reviewed-by: Keith Busch <keith.busch@xxxxxxxxx> > Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx> > --- > block/blk-mq.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/block/blk-mq.c b/block/blk-mq.c > index 3ff3d7b..b8ef489 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -2212,6 +2212,10 @@ static int blk_mq_hctx_notify_dead(unsigned int cpu, > struct hlist_node *node) > enum hctx_type type; > > hctx = hlist_entry_safe(node, struct blk_mq_hw_ctx, cpuhp_dead); > + > + if (!cpumask_test_cpu(cpu, hctx->cpumask)) > + return 0; > + > ctx = __blk_mq_get_ctx(hctx->queue, cpu); > type = hctx->type; > > -- > 2.7.4
