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);
+}
+
+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);
+}
+
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
_______________________________________________
Virtualization mailing list
Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
https://lists.linuxfoundation.org/mailman/listinfo/virtualization
