> On 04-Jan-2024, at 6:14 AM, Hao Xiang <hao.xi...@bytedance.com> wrote:
>
> From: Juan Quintela <quint...@redhat.com>
>
> This implements the zero page dection and handling.
>
> Signed-off-by: Juan Quintela <quint...@redhat.com>
> ---
> migration/multifd.c | 41 +++++++++++++++++++++++++++++++++++++++--
> migration/multifd.h | 5 +++++
> 2 files changed, 44 insertions(+), 2 deletions(-)
>
> diff --git a/migration/multifd.c b/migration/multifd.c
> index 5a1f50c7e8..756673029d 100644
> --- a/migration/multifd.c
> +++ b/migration/multifd.c
> @@ -11,6 +11,7 @@
> */
>
> #include "qemu/osdep.h"
> +#include "qemu/cutils.h"
> #include "qemu/rcu.h"
> #include "exec/target_page.h"
> #include "sysemu/sysemu.h"
> @@ -279,6 +280,12 @@ static void multifd_send_fill_packet(MultiFDSendParams
> *p)
>
> packet->offset[i] = cpu_to_be64(temp);
> }
> + for (i = 0; i < p->zero_num; i++) {
> + /* there are architectures where ram_addr_t is 32 bit */
> + uint64_t temp = p->zero[i];
> +
> + packet->offset[p->normal_num + i] = cpu_to_be64(temp);
> + }
> }
>
> static int multifd_recv_unfill_packet(MultiFDRecvParams *p, Error **errp)
> @@ -361,6 +368,18 @@ static int multifd_recv_unfill_packet(MultiFDRecvParams
> *p, Error **errp)
> p->normal[i] = offset;
> }
>
> + for (i = 0; i < p->zero_num; i++) {
> + uint64_t offset = be64_to_cpu(packet->offset[p->normal_num + i]);
> +
> + if (offset > (p->block->used_length - p->page_size)) {
> + error_setg(errp, "multifd: offset too long %" PRIu64
> + " (max " RAM_ADDR_FMT ")",
> + offset, p->block->used_length);
> + return -1;
> + }
> + p->zero[i] = offset;
> + }
> +
> return 0;
> }
>
> @@ -664,6 +683,8 @@ static void *multifd_send_thread(void *opaque)
> MultiFDSendParams *p = opaque;
> MigrationThread *thread = NULL;
> Error *local_err = NULL;
> + /* qemu older than 8.2 don't understand zero page on multifd channel */
> + bool use_zero_page = !migrate_use_main_zero_page();
> int ret = 0;
> bool use_zero_copy_send = migrate_zero_copy_send();
>
> @@ -689,6 +710,7 @@ static void *multifd_send_thread(void *opaque)
> qemu_mutex_lock(&p->mutex);
>
> if (p->pending_job) {
> + RAMBlock *rb = p->pages->block;
> uint64_t packet_num = p->packet_num;
> uint32_t flags;
> p->normal_num = 0;
> @@ -701,8 +723,16 @@ static void *multifd_send_thread(void *opaque)
> }
>
> for (int i = 0; i < p->pages->num; i++) {
> - p->normal[p->normal_num] = p->pages->offset[i];
> - p->normal_num++;
> + uint64_t offset = p->pages->offset[i];
> + if (use_zero_page &&
> + buffer_is_zero(rb->host + offset, p->page_size)) {
> + p->zero[p->zero_num] = offset;
> + p->zero_num++;
> + ram_release_page(rb->idstr, offset);
> + } else {
> + p->normal[p->normal_num] = offset;
> + p->normal_num++;
> + }
> }
>
> if (p->normal_num) {
> @@ -1155,6 +1185,13 @@ static void *multifd_recv_thread(void *opaque)
> }
> }
>
> + for (int i = 0; i < p->zero_num; i++) {
> + void *page = p->host + p->zero[i];
> + if (!buffer_is_zero(page, p->page_size)) {
> + memset(page, 0, p->page_size);
> + }
> + }
> +
I am wondering if zeroing the zero page on the destination can also be
offloaded to DSA. Can it help in reducing cpu consumption on the destination in
case of multifd-based migration?
> if (flags & MULTIFD_FLAG_SYNC) {
> qemu_sem_post(&multifd_recv_state->sem_sync);
> qemu_sem_wait(&p->sem_sync);
> diff --git a/migration/multifd.h b/migration/multifd.h
> index d587b0e19c..13762900d4 100644
> --- a/migration/multifd.h
> +++ b/migration/multifd.h
> @@ -53,6 +53,11 @@ typedef struct {
> uint32_t unused32[1]; /* Reserved for future use */
> uint64_t unused64[3]; /* Reserved for future use */
> char ramblock[256];
> + /*
> + * This array contains the pointers to:
> + * - normal pages (initial normal_pages entries)
> + * - zero pages (following zero_pages entries)
> + */
> uint64_t offset[];
> } __attribute__((packed)) MultiFDPacket_t;
>
> --
> 2.30.2
>
>
>
