Re: [PATCH 08/13] nvme-pci: remove the CQ lock for interrupt driven queues
From: Keith Busch <hidden>
Date: 2018-11-29 21:11:37
Also in:
linux-nvme
On Thu, Nov 29, 2018 at 08:13:05PM +0100, Christoph Hellwig wrote:
quoted hunk ↗ jump to hunk
@@ -1050,12 +1051,16 @@ static irqreturn_t nvme_irq(int irq, void *data) irqreturn_t ret = IRQ_NONE; u16 start, end; - spin_lock(&nvmeq->cq_lock); + /* + * The rmb/wmb pair ensures we see all updates from a previous run of + * the irq handler, even if that was on another CPU. + */ + rmb(); if (nvmeq->cq_head != nvmeq->last_cq_head) ret = IRQ_HANDLED; nvme_process_cq(nvmeq, &start, &end, -1); nvmeq->last_cq_head = nvmeq->cq_head; - spin_unlock(&nvmeq->cq_lock); + wmb(); if (start != end) { nvme_complete_cqes(nvmeq, start, end);
We saved the "start, end" only so we could do the real completion without holding a queue lock. Since you're not using a lock anymore, a further optimization can complete the CQE inline with moving the cq head so that we don't go through queue twice. That can be a follow on, though, this patch looks fine. Reviewed-by: Keith Busch <redacted>