Re: [Qemu-devel] [PATCH v5 33/45] Page request: Process incoming page request

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, Feb 25, 2015 at 04:51:56PM +0000, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> 
> On receiving MIG_RPCOMM_REQ_PAGES look up the address and
> queue the page.
> 
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> ---
>  arch_init.c                   | 55 +++++++++++++++++++++++++++++++++++++++++++
>  include/exec/cpu-all.h        |  2 --
>  include/migration/migration.h | 21 +++++++++++++++++
>  include/qemu/typedefs.h       |  1 +
>  migration/migration.c         | 33 +++++++++++++++++++++++++-
>  trace-events                  |  3 ++-
>  6 files changed, 111 insertions(+), 4 deletions(-)
> 
> diff --git a/arch_init.c b/arch_init.c
> index d2c4457..9d8fc6b 100644
> --- a/arch_init.c
> +++ b/arch_init.c
> @@ -669,6 +669,61 @@ static int ram_save_page(QEMUFile *f, RAMBlock* block, ram_addr_t offset,
>  }
>  
>  /*
> + * Queue the pages for transmission, e.g. a request from postcopy destination
> + *   ms: MigrationStatus in which the queue is held
> + *   rbname: The RAMBlock the request is for - may be NULL (to mean reuse last)
> + *   start: Offset from the start of the RAMBlock
> + *   len: Length (in bytes) to send
> + *   Return: 0 on success
> + */
> +int ram_save_queue_pages(MigrationState *ms, const char *rbname,
> +                         ram_addr_t start, ram_addr_t len)
> +{
> +    RAMBlock *ramblock;
> +
> +    if (!rbname) {
> +        /* Reuse last RAMBlock */
> +        ramblock = ms->last_req_rb;
> +
> +        if (!ramblock) {
> +            /*
> +             * Shouldn't happen, we can't reuse the last RAMBlock if
> +             * it's the 1st request.
> +             */
> +            error_report("ram_save_queue_pages no previous block");
> +            return -1;
> +        }
> +    } else {
> +        ramblock = ram_find_block(rbname);
> +
> +        if (!ramblock) {
> +            /* We shouldn't be asked for a non-existent RAMBlock */
> +            error_report("ram_save_queue_pages no block '%s'", rbname);
> +            return -1;
> +        }
> +    }
> +    trace_ram_save_queue_pages(ramblock->idstr, start, len);
> +    if (start+len > ramblock->used_length) {
> +        error_report("%s request overrun start=%zx len=%zx blocklen=%zx",
> +                     __func__, start, len, ramblock->used_length);
> +        return -1;
> +    }
> +
> +    struct MigrationSrcPageRequest *new_entry =
> +        g_malloc0(sizeof(struct MigrationSrcPageRequest));
> +    new_entry->rb = ramblock;
> +    new_entry->offset = start;
> +    new_entry->len = len;
> +    ms->last_req_rb = ramblock;
> +
> +    qemu_mutex_lock(&ms->src_page_req_mutex);
> +    QSIMPLEQ_INSERT_TAIL(&ms->src_page_requests, new_entry, next_req);
> +    qemu_mutex_unlock(&ms->src_page_req_mutex);
> +
> +    return 0;
> +}
> +
> +/*
>   * ram_find_and_save_block: Finds a page to send and sends it to f
>   *
>   * Returns:  The number of bytes written.
> diff --git a/include/exec/cpu-all.h b/include/exec/cpu-all.h
> index 2c48286..3088000 100644
> --- a/include/exec/cpu-all.h
> +++ b/include/exec/cpu-all.h
> @@ -265,8 +265,6 @@ CPUArchState *cpu_copy(CPUArchState *env);
>  
>  /* memory API */
>  
> -typedef struct RAMBlock RAMBlock;
> -
>  struct RAMBlock {
>      struct MemoryRegion *mr;
>      uint8_t *host;
> diff --git a/include/migration/migration.h b/include/migration/migration.h
> index 2c15d63..b1c7cad 100644
> --- a/include/migration/migration.h
> +++ b/include/migration/migration.h
> @@ -100,6 +100,18 @@ MigrationIncomingState *migration_incoming_get_current(void);
>  MigrationIncomingState *migration_incoming_state_new(QEMUFile *f);
>  void migration_incoming_state_destroy(void);
>  
> +/*
> + * An outstanding page request, on the source, having been received
> + * and queued
> + */
> +struct MigrationSrcPageRequest {
> +    RAMBlock *rb;
> +    hwaddr    offset;
> +    hwaddr    len;
> +
> +    QSIMPLEQ_ENTRY(MigrationSrcPageRequest) next_req;
> +};
> +
>  struct MigrationState
>  {
>      int64_t bandwidth_limit;
> @@ -142,6 +154,12 @@ struct MigrationState
>       * of the postcopy phase
>       */
>      unsigned long *sentmap;
> +
> +    /* Queue of outstanding page requests from the destination */
> +    QemuMutex src_page_req_mutex;
> +    QSIMPLEQ_HEAD(src_page_requests, MigrationSrcPageRequest) src_page_requests;
> +    /* The RAMBlock used in the last src_page_request */
> +    RAMBlock *last_req_rb;
>  };
>  
>  void process_incoming_migration(QEMUFile *f);
> @@ -276,6 +294,9 @@ size_t ram_control_save_page(QEMUFile *f, ram_addr_t block_offset,
>                               ram_addr_t offset, size_t size,
>                               int *bytes_sent);
>  
> +int ram_save_queue_pages(MigrationState *ms, const char *rbname,
> +                         ram_addr_t start, ram_addr_t len);
> +
>  PostcopyState postcopy_state_get(MigrationIncomingState *mis);
>  
>  /* Set the state and return the old state */
> diff --git a/include/qemu/typedefs.h b/include/qemu/typedefs.h
> index 0651275..396044d 100644
> --- a/include/qemu/typedefs.h
> +++ b/include/qemu/typedefs.h
> @@ -73,6 +73,7 @@ typedef struct QEMUSGList QEMUSGList;
>  typedef struct QEMUSizedBuffer QEMUSizedBuffer;
>  typedef struct QEMUTimerListGroup QEMUTimerListGroup;
>  typedef struct QEMUTimer QEMUTimer;
> +typedef struct RAMBlock RAMBlock;
>  typedef struct Range Range;
>  typedef struct SerialState SerialState;
>  typedef struct SHPCDevice SHPCDevice;
> diff --git a/migration/migration.c b/migration/migration.c
> index 2e9d0dd..939f426 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -26,6 +26,8 @@
>  #include "qemu/thread.h"
>  #include "qmp-commands.h"
>  #include "trace.h"
> +#include "exec/memory.h"
> +#include "exec/address-spaces.h"
>  
>  enum MigrationPhase {
>      MIG_STATE_ERROR = -1,
> @@ -495,6 +497,15 @@ static void migrate_fd_cleanup(void *opaque)
>  
>      migrate_fd_cleanup_src_rp(s);
>  
> +    /* This queue generally should be empty - but in the case of a failed
> +     * migration might have some droppings in.
> +     */
> +    struct MigrationSrcPageRequest *mspr, *next_mspr;
> +    QSIMPLEQ_FOREACH_SAFE(mspr, &s->src_page_requests, next_req, next_mspr) {
> +        QSIMPLEQ_REMOVE_HEAD(&s->src_page_requests, next_req);
> +        g_free(mspr);
> +    }
> +
>      if (s->file) {
>          trace_migrate_fd_cleanup();
>          qemu_mutex_unlock_iothread();
> @@ -613,6 +624,9 @@ MigrationState *migrate_init(const MigrationParams *params)
>      s->state = MIG_STATE_SETUP;
>      trace_migrate_set_state(MIG_STATE_SETUP);
>  
> +    qemu_mutex_init(&s->src_page_req_mutex);
> +    QSIMPLEQ_INIT(&s->src_page_requests);
> +
>      s->total_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
>      return s;
>  }
> @@ -826,7 +840,24 @@ static void source_return_path_bad(MigrationState *s)
>  static void migrate_handle_rp_req_pages(MigrationState *ms, const char* rbname,
>                                         ram_addr_t start, ram_addr_t len)
>  {
> -    trace_migrate_handle_rp_req_pages(start, len);
> +    trace_migrate_handle_rp_req_pages(rbname, start, len);
> +
> +    /* Round everything up to our host page size */
> +    long our_host_ps = getpagesize();
> +    if (start & (our_host_ps-1)) {
> +        long roundings = start & (our_host_ps-1);
> +        start -= roundings;
> +        len += roundings;
> +    }
> +    if (len & (our_host_ps-1)) {
> +        long roundings = len & (our_host_ps-1);
> +        len -= roundings;
> +        len += our_host_ps;
> +    }

Why is it necessary to round out to host page size on the source?  I
understand why the host page size is relevant on the destination, due
to the userfaultfd and atomic populate constraints, but not on the source.

> +    if (ram_save_queue_pages(ms, rbname, start, len)) {
> +        source_return_path_bad(ms);
> +    }
>  }
>  
>  /*
> diff --git a/trace-events b/trace-events
> index 9bedee4..8a0d70d 100644
> --- a/trace-events
> +++ b/trace-events
> @@ -1218,6 +1218,7 @@ migration_bitmap_sync_start(void) ""
>  migration_bitmap_sync_end(uint64_t dirty_pages) "dirty_pages %" PRIu64""
>  migration_throttle(void) ""
>  ram_postcopy_send_discard_bitmap(void) ""
> +ram_save_queue_pages(const char *rbname, size_t start, size_t len) "%s: start: %zx len: %zx"
>  
>  # hw/display/qxl.c
>  disable qxl_interface_set_mm_time(int qid, uint32_t mm_time) "%d %d"
> @@ -1404,7 +1405,7 @@ migrate_fd_error(void) ""
>  migrate_fd_cancel(void) ""
>  migrate_pending(uint64_t size, uint64_t max, uint64_t post, uint64_t nonpost) "pending size %" PRIu64 " max %" PRIu64 " (post=%" PRIu64 " nonpost=%" PRIu64 ")"
>  migrate_send_rp_message(int cmd, uint16_t len) "cmd=%d, len=%d"
> -migrate_handle_rp_req_pages(size_t start, size_t len) "at %zx for len %zx"
> +migrate_handle_rp_req_pages(const char *rbname, size_t start, size_t len) "in %s at %zx len %zx"
>  migration_thread_after_loop(void) ""
>  migration_thread_file_err(void) ""
>  migration_thread_setup_complete(void) ""

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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