On Tue, 5 Jul 2022 at 10:25, Jinhao Fan <fanjinhao...@ict.ac.cn> wrote:
>
> Add property "ioeventfd" which is enabled by default. When this is
> enabled, updates on the doorbell registers will cause KVM to signal
> an event to the QEMU main loop to handle the doorbell updates.
> Therefore, instead of letting the vcpu thread run both guest VM and
> IO emulation, we now use the main loop thread to do IO emulation and
> thus the vcpu thread has more cycles for the guest VM.
>
> Since ioeventfd does not tell us the exact value that is written, it is
> only useful when shadow doorbell buffer is enabled, where we check
> for the value in the shadow doorbell buffer when we get the doorbell
> update event.
>
> IOPS comparison on Linux 5.19-rc2: (Unit: KIOPS)
>
> qd 1 4 16 64
> qemu 35 121 176 153
> ioeventfd 41 133 258 313
Nice
>
> Changes since v3:
> - Do not deregister ioeventfd when it was not enabled on a SQ/CQ
>
> Signed-off-by: Jinhao Fan <fanjinhao...@ict.ac.cn>
> ---
> hw/nvme/ctrl.c | 114 ++++++++++++++++++++++++++++++++++++++++++++++++-
> hw/nvme/nvme.h | 5 +++
> 2 files changed, 118 insertions(+), 1 deletion(-)
>
> diff --git a/hw/nvme/ctrl.c b/hw/nvme/ctrl.c
> index c952c34f94..4b75c5f549 100644
> --- a/hw/nvme/ctrl.c
> +++ b/hw/nvme/ctrl.c
> @@ -1374,7 +1374,14 @@ static void nvme_enqueue_req_completion(NvmeCQueue
> *cq, NvmeRequest *req)
>
> QTAILQ_REMOVE(&req->sq->out_req_list, req, entry);
> QTAILQ_INSERT_TAIL(&cq->req_list, req, entry);
> - timer_mod(cq->timer, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + 500);
> +
> + if (req->sq->ioeventfd_enabled) {
> + /* Post CQE directly since we are in main loop thread */
> + nvme_post_cqes(cq);
> + } else {
> + /* Schedule the timer to post CQE later since we are in vcpu thread
> */
> + timer_mod(cq->timer, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + 500);
> + }
This change is somewhat independent of ioeventfd. I wonder how much of
the performance improvement is due to the sq ioeventfd and how much is
due to bypassing the completion timer.
In the qd=1 case I expect the completion timer to increase latency and
hurt performance. In the qd=64 case the timer increases batching,
reduces CPU consumption, and probably improves performance.
It would be nice to measure this in isolation, independently of
ioeventfd/IOThreads.
> }
>
> static void nvme_process_aers(void *opaque)
> @@ -4195,10 +4202,82 @@ static uint16_t nvme_io_cmd(NvmeCtrl *n, NvmeRequest
> *req)
> return NVME_INVALID_OPCODE | NVME_DNR;
> }
>
> +static void nvme_cq_notifier(EventNotifier *e)
> +{
> + NvmeCQueue *cq = container_of(e, NvmeCQueue, notifier);
> + NvmeCtrl *n = cq->ctrl;
> +
> + event_notifier_test_and_clear(&cq->notifier);
> +
> + nvme_update_cq_head(cq);
> +
> + if (cq->tail == cq->head) {
> + if (cq->irq_enabled) {
> + n->cq_pending--;
> + }
> +
> + nvme_irq_deassert(n, cq);
> + }
> +
> + nvme_post_cqes(cq);
> +}
> +
> +static int nvme_init_cq_ioeventfd(NvmeCQueue *cq)
> +{
> + NvmeCtrl *n = cq->ctrl;
> + uint16_t offset = (cq->cqid << 3) + (1 << 2);
Too many...
> + int ret;
> +
> + ret = event_notifier_init(&cq->notifier, 0);
> + if (ret < 0) {
> + return ret;
> + }
> +
> + event_notifier_set_handler(&cq->notifier, nvme_cq_notifier);
> + memory_region_add_eventfd(&n->iomem,
> + 0x1000 + offset, 4, false, 0, &cq->notifier);
...magic numbers. Please use constants so it's clear what << 3, (1 <<
2), 0x1000, etc mean.
> +
> + return 0;
> +}
> +
> +static void nvme_sq_notifier(EventNotifier *e)
> +{
> + NvmeSQueue *sq = container_of(e, NvmeSQueue, notifier);
> +
> + event_notifier_test_and_clear(&sq->notifier);
> +
> + nvme_process_sq(sq);
> +}
> +
> +static int nvme_init_sq_ioeventfd(NvmeSQueue *sq)
> +{
> + NvmeCtrl *n = sq->ctrl;
> + uint16_t offset = sq->sqid << 3;
> + int ret;
> +
> + ret = event_notifier_init(&sq->notifier, 0);
> + if (ret < 0) {
> + return ret;
> + }
> +
> + event_notifier_set_handler(&sq->notifier, nvme_sq_notifier);
> + memory_region_add_eventfd(&n->iomem,
> + 0x1000 + offset, 4, false, 0, &sq->notifier);
> +
> + return 0;
> +}
> +
> static void nvme_free_sq(NvmeSQueue *sq, NvmeCtrl *n)
> {
> + uint16_t offset = sq->sqid << 3;
> +
> n->sq[sq->sqid] = NULL;
> timer_free(sq->timer);
> + if (sq->ioeventfd_enabled) {
> + memory_region_del_eventfd(&n->iomem,
> + 0x1000 + offset, 4, false, 0,
> &sq->notifier);
> + event_notifier_cleanup(&sq->notifier);
> + }
> g_free(sq->io_req);
> if (sq->sqid) {
> g_free(sq);
> @@ -4271,6 +4350,12 @@ static void nvme_init_sq(NvmeSQueue *sq, NvmeCtrl *n,
> uint64_t dma_addr,
> if (n->dbbuf_enabled) {
> sq->db_addr = n->dbbuf_dbs + (sqid << 3);
> sq->ei_addr = n->dbbuf_eis + (sqid << 3);
> +
> + if (n->params.ioeventfd && sq->sqid != 0) {
> + if (!nvme_init_sq_ioeventfd(sq)) {
> + sq->ioeventfd_enabled = true;
> + }
> + }
> }
>
> assert(n->cq[cqid]);
> @@ -4575,8 +4660,15 @@ static uint16_t nvme_get_log(NvmeCtrl *n, NvmeRequest
> *req)
>
> static void nvme_free_cq(NvmeCQueue *cq, NvmeCtrl *n)
> {
> + uint16_t offset = (cq->cqid << 3) + (1 << 2);
> +
> n->cq[cq->cqid] = NULL;
> timer_free(cq->timer);
> + if (cq->ioeventfd_enabled) {
> + memory_region_del_eventfd(&n->iomem,
> + 0x1000 + offset, 4, false, 0,
> &cq->notifier);
> + event_notifier_cleanup(&cq->notifier);
> + }
> if (msix_enabled(&n->parent_obj)) {
> msix_vector_unuse(&n->parent_obj, cq->vector);
> }
> @@ -4635,6 +4727,12 @@ static void nvme_init_cq(NvmeCQueue *cq, NvmeCtrl *n,
> uint64_t dma_addr,
> if (n->dbbuf_enabled) {
> cq->db_addr = n->dbbuf_dbs + (cqid << 3) + (1 << 2);
> cq->ei_addr = n->dbbuf_eis + (cqid << 3) + (1 << 2);
> +
> + if (n->params.ioeventfd && cqid != 0) {
> + if (!nvme_init_cq_ioeventfd(cq)) {
> + cq->ioeventfd_enabled = true;
> + }
> + }
> }
> n->cq[cqid] = cq;
> cq->timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, nvme_post_cqes, cq);
> @@ -5793,6 +5891,7 @@ static uint16_t nvme_dbbuf_config(NvmeCtrl *n, const
> NvmeRequest *req)
> uint64_t dbs_addr = le64_to_cpu(req->cmd.dptr.prp1);
> uint64_t eis_addr = le64_to_cpu(req->cmd.dptr.prp2);
> int i;
> + int ret;
>
> /* Address should be page aligned */
> if (dbs_addr & (n->page_size - 1) || eis_addr & (n->page_size - 1)) {
> @@ -5818,6 +5917,12 @@ static uint16_t nvme_dbbuf_config(NvmeCtrl *n, const
> NvmeRequest *req)
> sq->ei_addr = eis_addr + (i << 3);
> pci_dma_write(&n->parent_obj, sq->db_addr, &sq->tail,
> sizeof(sq->tail));
> +
> + if (n->params.ioeventfd && sq->sqid != 0) {
> + if (!nvme_init_sq_ioeventfd(sq)) {
> + sq->ioeventfd_enabled = true;
> + }
> + }
> }
>
> if (cq) {
> @@ -5826,6 +5931,12 @@ static uint16_t nvme_dbbuf_config(NvmeCtrl *n, const
> NvmeRequest *req)
> cq->ei_addr = eis_addr + (i << 3) + (1 << 2);
> pci_dma_write(&n->parent_obj, cq->db_addr, &cq->head,
> sizeof(cq->head));
> +
> + if (n->params.ioeventfd && cq->cqid != 0) {
> + if (!nvme_init_cq_ioeventfd(cq)) {
> + cq->ioeventfd_enabled = true;
> + }
> + }
> }
> }
>
> @@ -7040,6 +7151,7 @@ static Property nvme_props[] = {
> DEFINE_PROP_UINT8("zoned.zasl", NvmeCtrl, params.zasl, 0),
> DEFINE_PROP_BOOL("zoned.auto_transition", NvmeCtrl,
> params.auto_transition_zones, true),
> + DEFINE_PROP_BOOL("ioeventfd", NvmeCtrl, params.ioeventfd, true),
> DEFINE_PROP_END_OF_LIST(),
> };
>
> diff --git a/hw/nvme/nvme.h b/hw/nvme/nvme.h
> index 4452e4b1bf..2a9beea0c8 100644
> --- a/hw/nvme/nvme.h
> +++ b/hw/nvme/nvme.h
> @@ -369,6 +369,8 @@ typedef struct NvmeSQueue {
> uint64_t db_addr;
> uint64_t ei_addr;
> QEMUTimer *timer;
> + EventNotifier notifier;
> + bool ioeventfd_enabled;
> NvmeRequest *io_req;
> QTAILQ_HEAD(, NvmeRequest) req_list;
> QTAILQ_HEAD(, NvmeRequest) out_req_list;
> @@ -388,6 +390,8 @@ typedef struct NvmeCQueue {
> uint64_t db_addr;
> uint64_t ei_addr;
> QEMUTimer *timer;
> + EventNotifier notifier;
> + bool ioeventfd_enabled;
> QTAILQ_HEAD(, NvmeSQueue) sq_list;
> QTAILQ_HEAD(, NvmeRequest) req_list;
> } NvmeCQueue;
> @@ -410,6 +414,7 @@ typedef struct NvmeParams {
> uint8_t zasl;
> bool auto_transition_zones;
> bool legacy_cmb;
> + bool ioeventfd;
> } NvmeParams;
>
> typedef struct NvmeCtrl {
> --
> 2.25.1
>
>
