Messages in this thread | | | Subject | Re: [PATCH] nvme: Acknowledge completion queue on each iteration | From | Sinan Kaya <> | Date | Wed, 19 Jul 2017 06:37:22 -0400 |
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On 7/19/2017 5:20 AM, Sagi Grimberg wrote: >> Code is moving the completion queue doorbell after processing all completed >> events and sending callbacks to the block layer on each iteration. >> >> This is causing a performance drop when a lot of jobs are queued towards >> the HW. Move the completion queue doorbell on each loop instead and allow new >> jobs to be queued by the HW. >> >> Signed-off-by: Sinan Kaya <okaya@codeaurora.org> >> --- >> drivers/nvme/host/pci.c | 5 ++--- >> 1 file changed, 2 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c >> index d10d2f2..33d9b5b 100644 >> --- a/drivers/nvme/host/pci.c >> +++ b/drivers/nvme/host/pci.c >> @@ -810,13 +810,12 @@ static void nvme_process_cq(struct nvme_queue *nvmeq) >> while (nvme_read_cqe(nvmeq, &cqe)) { >> nvme_handle_cqe(nvmeq, &cqe); >> + nvme_ring_cq_doorbell(nvmeq); >> consumed++; >> } >> - if (consumed) { >> - nvme_ring_cq_doorbell(nvmeq); >> + if (consumed) >> nvmeq->cqe_seen = 1; >> - } >> } > > Agree with Keith that this is definitely not the way to go, it > adds mmio operations in the hot path with very little gain (if > at all). >
Understood, different architectures might have different latency accessing the HW registers. It might be expansive on some platform like you indicated and this change would make it worse.
I'm doing a self NACK as well.
-- Sinan Kaya Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc. Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
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