Re: [External] Re: [PATCH v7 09/12] migration/multifd: Enable DSA offloading in multifd sender path.

[Fabiano Rosas <farosas@suse.de>]

Yichen Wang <yichen.wang@bytedance.com> writes:

> On Thu, Nov 21, 2024 at 12:52 PM Fabiano Rosas <farosas@suse.de> wrote:
>>
>> Yichen Wang <yichen.wang@bytedance.com> writes:
>>
>> > From: Hao Xiang <hao.xiang@linux.dev>
>> >
>> > Multifd sender path gets an array of pages queued by the migration
>> > thread. It performs zero page checking on every page in the array.
>> > The pages are classfied as either a zero page or a normal page. This
>> > change uses Intel DSA to offload the zero page checking from CPU to
>> > the DSA accelerator. The sender thread submits a batch of pages to DSA
>> > hardware and waits for the DSA completion thread to signal for work
>> > completion.
>> >
>> > Signed-off-by: Hao Xiang <hao.xiang@linux.dev>
>> > Signed-off-by: Yichen Wang <yichen.wang@bytedance.com>
>> > ---
>> >  migration/multifd-zero-page.c | 129 ++++++++++++++++++++++++++++++----
>> >  migration/multifd.c           |  29 +++++++-
>> >  migration/multifd.h           |   5 ++
>> >  3 files changed, 147 insertions(+), 16 deletions(-)
>> >
>> > diff --git a/migration/multifd-zero-page.c b/migration/multifd-zero-page.c
>> > index f1e988a959..639aed9f6b 100644
>> > --- a/migration/multifd-zero-page.c
>> > +++ b/migration/multifd-zero-page.c
>> > @@ -21,7 +21,9 @@
>> >
>> >  static bool multifd_zero_page_enabled(void)
>> >  {
>> > -    return migrate_zero_page_detection() == ZERO_PAGE_DETECTION_MULTIFD;
>> > +    ZeroPageDetection curMethod = migrate_zero_page_detection();
>> > +    return (curMethod == ZERO_PAGE_DETECTION_MULTIFD ||
>> > +            curMethod == ZERO_PAGE_DETECTION_DSA_ACCEL);
>> >  }
>> >
>> >  static void swap_page_offset(ram_addr_t *pages_offset, int a, int b)
>> > @@ -37,26 +39,49 @@ static void swap_page_offset(ram_addr_t *pages_offset, int a, int b)
>> >      pages_offset[b] = temp;
>> >  }
>> >
>> > +#ifdef CONFIG_DSA_OPT
>> > +
>> > +static void swap_result(bool *results, int a, int b)
>> > +{
>> > +    bool temp;
>> > +
>> > +    if (a == b) {
>> > +        return;
>> > +    }
>> > +
>> > +    temp = results[a];
>> > +    results[a] = results[b];
>> > +    results[b] = temp;
>> > +}
>> > +
>> >  /**
>> > - * multifd_send_zero_page_detect: Perform zero page detection on all pages.
>> > + * zero_page_detect_dsa: Perform zero page detection using
>> > + * Intel Data Streaming Accelerator (DSA).
>> >   *
>> > - * Sorts normal pages before zero pages in p->pages->offset and updates
>> > - * p->pages->normal_num.
>> > + * Sorts normal pages before zero pages in pages->offset and updates
>> > + * pages->normal_num.
>> >   *
>> >   * @param p A pointer to the send params.
>> >   */
>> > -void multifd_send_zero_page_detect(MultiFDSendParams *p)
>> > +static void zero_page_detect_dsa(MultiFDSendParams *p)
>> >  {
>> >      MultiFDPages_t *pages = &p->data->u.ram;
>> >      RAMBlock *rb = pages->block;
>> > -    int i = 0;
>> > -    int j = pages->num - 1;
>> > +    bool *results = p->dsa_batch_task->results;
>> >
>> > -    if (!multifd_zero_page_enabled()) {
>> > -        pages->normal_num = pages->num;
>> > -        goto out;
>> > +    for (int i = 0; i < pages->num; i++) {
>> > +        p->dsa_batch_task->addr[i] =
>> > +            (ram_addr_t)(rb->host + pages->offset[i]);
>> >      }
>> >
>> > +    buffer_is_zero_dsa_batch_sync(p->dsa_batch_task,
>> > +                                  (const void **)p->dsa_batch_task->addr,
>> > +                                  pages->num,
>> > +                                  multifd_ram_page_size());
>> > +
>> > +    int i = 0;
>> > +    int j = pages->num - 1;
>> > +
>> >      /*
>> >       * Sort the page offset array by moving all normal pages to
>> >       * the left and all zero pages to the right of the array.
>> > @@ -64,23 +89,39 @@ void multifd_send_zero_page_detect(MultiFDSendParams *p)
>> >      while (i <= j) {
>> >          uint64_t offset = pages->offset[i];
>> >
>> > -        if (!buffer_is_zero(rb->host + offset, multifd_ram_page_size())) {
>> > +        if (!results[i]) {
>> >              i++;
>> >              continue;
>> >          }
>> >
>> > +        swap_result(results, i, j);
>> >          swap_page_offset(pages->offset, i, j);
>> >          ram_release_page(rb->idstr, offset);
>> >          j--;
>> >      }
>> >
>> >      pages->normal_num = i;
>> > +}
>> >
>> > -out:
>> > -    stat64_add(&mig_stats.normal_pages, pages->normal_num);
>> > -    stat64_add(&mig_stats.zero_pages, pages->num - pages->normal_num);
>> > +void multifd_dsa_cleanup(void)
>> > +{
>> > +    qemu_dsa_cleanup();
>> > +}
>> > +
>> > +#else
>> > +
>> > +static void zero_page_detect_dsa(MultiFDSendParams *p)
>> > +{
>> > +    g_assert_not_reached();
>> > +}
>> > +
>> > +void multifd_dsa_cleanup(void)
>> > +{
>> > +    return ;
>> >  }
>> >
>> > +#endif
>> > +
>> >  void multifd_recv_zero_page_process(MultiFDRecvParams *p)
>> >  {
>> >      for (int i = 0; i < p->zero_num; i++) {
>> > @@ -92,3 +133,63 @@ void multifd_recv_zero_page_process(MultiFDRecvParams *p)
>> >          }
>> >      }
>> >  }
>> > +
>> > +/**
>> > + * zero_page_detect_cpu: Perform zero page detection using CPU.
>> > + *
>> > + * Sorts normal pages before zero pages in p->pages->offset and updates
>> > + * p->pages->normal_num.
>> > + *
>> > + * @param p A pointer to the send params.
>> > + */
>> > +static void zero_page_detect_cpu(MultiFDSendParams *p)
>> > +{
>> > +    MultiFDPages_t *pages = &p->data->u.ram;
>> > +    RAMBlock *rb = pages->block;
>> > +    int i = 0;
>> > +    int j = pages->num - 1;
>> > +
>> > +    /*
>> > +     * Sort the page offset array by moving all normal pages to
>> > +     * the left and all zero pages to the right of the array.
>> > +     */
>> > +    while (i <= j) {
>> > +        uint64_t offset = pages->offset[i];
>> > +
>> > +        if (!buffer_is_zero(rb->host + offset, multifd_ram_page_size())) {
>> > +            i++;
>> > +            continue;
>> > +        }
>> > +
>> > +        swap_page_offset(pages->offset, i, j);
>> > +        ram_release_page(rb->idstr, offset);
>> > +        j--;
>> > +    }
>> > +
>> > +    pages->normal_num = i;
>> > +}
>> > +
>> > +/**
>> > + * multifd_send_zero_page_detect: Perform zero page detection on all pages.
>> > + *
>> > + * @param p A pointer to the send params.
>> > + */
>> > +void multifd_send_zero_page_detect(MultiFDSendParams *p)
>> > +{
>> > +    MultiFDPages_t *pages = &p->data->u.ram;
>> > +
>> > +    if (!multifd_zero_page_enabled()) {
>> > +        pages->normal_num = pages->num;
>> > +        goto out;
>> > +    }
>> > +
>> > +    if (qemu_dsa_is_running()) {
>> > +        zero_page_detect_dsa(p);
>> > +    } else {
>> > +        zero_page_detect_cpu(p);
>> > +    }
>> > +
>> > +out:
>> > +    stat64_add(&mig_stats.normal_pages, pages->normal_num);
>> > +    stat64_add(&mig_stats.zero_pages, pages->num - pages->normal_num);
>> > +}
>> > diff --git a/migration/multifd.c b/migration/multifd.c
>> > index 4374e14a96..689acceff2 100644
>> > --- a/migration/multifd.c
>> > +++ b/migration/multifd.c
>> > @@ -13,6 +13,7 @@
>> >  #include "qemu/osdep.h"
>> >  #include "qemu/cutils.h"
>> >  #include "qemu/rcu.h"
>> > +#include "qemu/dsa.h"
>> >  #include "exec/target_page.h"
>> >  #include "sysemu/sysemu.h"
>> >  #include "exec/ramblock.h"
>> > @@ -462,6 +463,8 @@ static bool multifd_send_cleanup_channel(MultiFDSendParams *p, Error **errp)
>> >      p->name = NULL;
>> >      g_free(p->data);
>> >      p->data = NULL;
>> > +    buffer_zero_batch_task_destroy(p->dsa_batch_task);
>> > +    p->dsa_batch_task = NULL;
>> >      p->packet_len = 0;
>> >      g_free(p->packet);
>> >      p->packet = NULL;
>> > @@ -493,6 +496,8 @@ void multifd_send_shutdown(void)
>> >
>> >      multifd_send_terminate_threads();
>> >
>> > +    multifd_dsa_cleanup();
>> > +
>> >      for (i = 0; i < migrate_multifd_channels(); i++) {
>> >          MultiFDSendParams *p = &multifd_send_state->params[i];
>> >          Error *local_err = NULL;
>> > @@ -814,11 +819,31 @@ bool multifd_send_setup(void)
>> >      uint32_t page_count = multifd_ram_page_count();
>> >      bool use_packets = multifd_use_packets();
>> >      uint8_t i;
>> > +    Error *local_err = NULL;
>> >
>> >      if (!migrate_multifd()) {
>> >          return true;
>> >      }
>> >
>> > +    if (s &&
>> > +        s->parameters.zero_page_detection == ZERO_PAGE_DETECTION_DSA_ACCEL) {
>> > +        // Populate the dsa device path from accel-path
>>
>> scripts/checkpatch.pl would have rejected this.
>>
>
> Sorry. I will make sure to run checkpatch.pl, unit test (both
> with/without DSA), before the send-email...
>
>> > +        const strList *accel_path = migrate_accel_path();
>> > +        g_autofree strList *dsa_parameter = g_malloc0(sizeof(strList));
>> > +        strList **tail = &dsa_parameter;
>> > +        while (accel_path) {
>> > +            if (strncmp(accel_path->value, "dsa:", 4) == 0) {
>> > +                QAPI_LIST_APPEND(tail, &accel_path->value[4]);
>> > +            }
>> > +            accel_path = accel_path->next;
>> > +        }
>>
>> The parsing of the parameter should be in options.c. In fact, Peter
>> suggested in v4 to make all of this a multifd_dsa_send_setup() or
>> multifd_dsa_init(), I think that's a good idea.
>>
>
> Will fix it in the next version.
>
>> > +        if (qemu_dsa_init(dsa_parameter, &local_err)) {
>> > +            ret = -1;
>>
>> migrate_set_error(s, local_err);
>> goto err;
>
> Will fix it in the next version. But here we can't goto err, because
> the cleanup() function will be called when setup() fails, and it has
> assumptions that a certain data structure is in place. If we exit
> earlier, the cleanup() function will complain and fail.
>

Which data structure? Is that multifd_send_state below? You could move
those before qemu_dsa_init if that's the case.

>>
>> > +        } else {
>> > +            qemu_dsa_start();
>> > +        }
>> > +    }
>> > +
>> >      thread_count = migrate_multifd_channels();
>> >      multifd_send_state = g_malloc0(sizeof(*multifd_send_state));
>> >      multifd_send_state->params = g_new0(MultiFDSendParams, thread_count);
>> > @@ -829,12 +854,12 @@ bool multifd_send_setup(void)
>> >
>> >      for (i = 0; i < thread_count; i++) {
>> >          MultiFDSendParams *p = &multifd_send_state->params[i];
>> > -        Error *local_err = NULL;
>> >
>> >          qemu_sem_init(&p->sem, 0);
>> >          qemu_sem_init(&p->sem_sync, 0);
>> >          p->id = i;
>> >          p->data = multifd_send_data_alloc();
>> > +        p->dsa_batch_task = buffer_zero_batch_task_init(page_count);
>> >
>> >          if (use_packets) {
>> >              p->packet_len = sizeof(MultiFDPacket_t)
>> > @@ -865,7 +890,6 @@ bool multifd_send_setup(void)
>> >
>> >      for (i = 0; i < thread_count; i++) {
>> >          MultiFDSendParams *p = &multifd_send_state->params[i];
>> > -        Error *local_err = NULL;
>> >
>> >          ret = multifd_send_state->ops->send_setup(p, &local_err);
>> >          if (ret) {
>> > @@ -1047,6 +1071,7 @@ void multifd_recv_cleanup(void)
>> >              qemu_thread_join(&p->thread);
>> >          }
>> >      }
>> > +    multifd_dsa_cleanup();
>> >      for (i = 0; i < migrate_multifd_channels(); i++) {
>> >          multifd_recv_cleanup_channel(&multifd_recv_state->params[i]);
>> >      }
>> > diff --git a/migration/multifd.h b/migration/multifd.h
>> > index 50d58c0c9c..e293ddbc1d 100644
>> > --- a/migration/multifd.h
>> > +++ b/migration/multifd.h
>> > @@ -15,6 +15,7 @@
>> >
>> >  #include "exec/target_page.h"
>> >  #include "ram.h"
>> > +#include "qemu/dsa.h"
>> >
>> >  typedef struct MultiFDRecvData MultiFDRecvData;
>> >  typedef struct MultiFDSendData MultiFDSendData;
>> > @@ -155,6 +156,9 @@ typedef struct {
>> >      bool pending_sync;
>> >      MultiFDSendData *data;
>> >
>> > +    /* Zero page checking batch task */
>> > +    QemuDsaBatchTask *dsa_batch_task;
>> > +
>> >      /* thread local variables. No locking required */
>> >
>> >      /* pointer to the packet */
>> > @@ -313,6 +317,7 @@ void multifd_send_fill_packet(MultiFDSendParams *p);
>> >  bool multifd_send_prepare_common(MultiFDSendParams *p);
>> >  void multifd_send_zero_page_detect(MultiFDSendParams *p);
>> >  void multifd_recv_zero_page_process(MultiFDRecvParams *p);
>> > +void multifd_dsa_cleanup(void);
>> >
>> >  static inline void multifd_send_prepare_header(MultiFDSendParams *p)
>> >  {