On 20/11/2015 09:11, Ming Lin wrote:
> On Thu, 2015-11-19 at 11:37 +0100, Paolo Bonzini wrote:
>>
>> On 18/11/2015 06:47, Ming Lin wrote:
>>> @@ -726,7 +798,11 @@ static void nvme_process_db(NvmeCtrl *n, hwaddr addr, int val)
>>> }
>>>
>>> start_sqs = nvme_cq_full(cq) ? 1 : 0;
>>> - cq->head = new_head;
>>> + /* When the mapped pointer memory area is setup, we don't rely on
>>> + * the MMIO written values to update the head pointer. */
>>> + if (!cq->db_addr) {
>>> + cq->head = new_head;
>>> + }
>>
>> You are still checking
>>
>> if (new_head >= cq->size) {
>> return;
>> }
>>
>> above. I think this is incorrect when the extension is present, and
>> furthermore it's the only case where val is being used.
>>
>> If you're not using val, you could use ioeventfd for the MMIO. An
>> ioeventfd cuts the MMIO cost by at least 55% and up to 70%. Here are
>> quick and dirty measurements from kvm-unit-tests's vmexit.flat
>> benchmark, on two very different machines:
>>
>> Haswell-EP Ivy Bridge i7
>> MMIO memory write 5100 -> 2250 (55%) 7000 -> 3000 (58%)
>> I/O port write 3800 -> 1150 (70%) 4100 -> 1800 (57%)
>>
>> You would need to allocate two eventfds for each qid, one for the sq and
>> one for the cq. Also, processing the queues is now bounced to the QEMU
>> iothread, so you can probably get rid of sq->timer and cq->timer.
>
> Here is a quick try.
> Too late now, I'll test it morning.
>
> Do you see obvious problem?
>
> diff --git a/hw/block/nvme.c b/hw/block/nvme.c
> index 3e1c38d..d28690d 100644
> --- a/hw/block/nvme.c
> +++ b/hw/block/nvme.c
> @@ -543,6 +543,44 @@ static uint16_t nvme_set_feature(NvmeCtrl *n, NvmeCmd *cmd, NvmeRequest *req)
> return NVME_SUCCESS;
> }
>
> +static void nvme_cq_notifier(EventNotifier *e)
> +{
> + NvmeCQueue *cq =
> + container_of(e, NvmeCQueue, notifier);
> +
> + nvme_post_cqes(cq);
> +}
> +
> +static void nvme_init_cq_eventfd(NvmeCQueue *cq)
> +{
> + NvmeCtrl *n = cq->ctrl;
> + uint16_t offset = (cq->cqid*2+1) * NVME_CAP_DSTRD(n->bar.cap);
> +
> + event_notifier_init(&cq->notifier, 0);
> + event_notifier_set_handler(&cq->notifier, nvme_cq_notifier);
> + memory_region_add_eventfd(&n->iomem,
> + 0x1000 + offset, 4, true, cq->cqid*2+1, &cq->notifier);
should be 0x1000 + offset, 4, false, 0, &cq->notifier
> +}
> +
> +static void nvme_sq_notifier(EventNotifier *e)
> +{
> + NvmeSQueue *sq =
> + container_of(e, NvmeSQueue, notifier);
> +
> + nvme_process_sq(sq);
> +}
> +
> +static void nvme_init_sq_eventfd(NvmeSQueue *sq)
> +{
> + NvmeCtrl *n = sq->ctrl;
> + uint16_t offset = sq->sqid * 2 * NVME_CAP_DSTRD(n->bar.cap);
> +
> + event_notifier_init(&sq->notifier, 0);
> + event_notifier_set_handler(&sq->notifier, nvme_sq_notifier);
> + memory_region_add_eventfd(&n->iomem,
> + 0x1000 + offset, 4, true, sq->sqid * 2, &sq->notifier);
likewise should be 0x1000 + offset, 4, false, 0, &sq->notifier
Otherwise looks good!
Paolo
> +}
> +
> static uint16_t nvme_set_db_memory(NvmeCtrl *n, const NvmeCmd *cmd)
> {
> uint64_t db_addr = le64_to_cpu(cmd->prp1);
> @@ -565,6 +603,7 @@ static uint16_t nvme_set_db_memory(NvmeCtrl *n, const NvmeCmd *cmd)
> /* Submission queue tail pointer location, 2 * QID * stride. */
> sq->db_addr = db_addr + 2 * i * 4;
> sq->eventidx_addr = eventidx_addr + 2 * i * 4;
> + nvme_init_sq_eventfd(sq);
> }
>
> if (cq != NULL) {
> @@ -572,6 +611,7 @@ static uint16_t nvme_set_db_memory(NvmeCtrl *n, const NvmeCmd *cmd)
> */
> cq->db_addr = db_addr + (2 * i + 1) * 4;
> cq->eventidx_addr = eventidx_addr + (2 * i + 1) * 4;
> + nvme_init_cq_eventfd(cq);
> }
> }
> return NVME_SUCCESS;
> @@ -793,7 +833,7 @@ static void nvme_process_db(NvmeCtrl *n, hwaddr addr, int val)
> }
>
> cq = n->cq[qid];
> - if (new_head >= cq->size) {
> + if (!cq->db_addr && new_head >= cq->size) {
> return;
> }
>
> diff --git a/hw/block/nvme.h b/hw/block/nvme.h
> index 82aeab4..608f202 100644
> --- a/hw/block/nvme.h
> +++ b/hw/block/nvme.h
> @@ -667,6 +667,7 @@ typedef struct NvmeSQueue {
> * do not go over this value will not result in MMIO writes (but will
> * still write the tail pointer to the "db_addr" location above). */
> uint64_t eventidx_addr;
> + EventNotifier notifier;
> } NvmeSQueue;
>
> typedef struct NvmeCQueue {
> @@ -689,6 +690,7 @@ typedef struct NvmeCQueue {
> * do not go over this value will not result in MMIO writes (but will
> * still write the head pointer to the "db_addr" location above). */
> uint64_t eventidx_addr;
> + EventNotifier notifier;
> } NvmeCQueue;
>
> typedef struct NvmeNamespace {
>
>>
>> Paolo
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