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Re: [Qemu-devel] [RFC 15/29] migration: allow fault thread to pause
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [RFC 15/29] migration: allow fault thread to pause |
Date: |
Tue, 1 Aug 2017 11:41:05 +0100 |
User-agent: |
Mutt/1.8.3 (2017-05-23) |
* Peter Xu (address@hidden) wrote:
> Allows the fault thread to stop handling page faults temporarily. When
> network failure happened (and if we expect a recovery afterwards), we
> should not allow the fault thread to continue sending things to source,
> instead, it should halt for a while until the connection is rebuilt.
>
> When the dest main thread noticed the failure, it kicks the fault thread
> to switch to pause state.
>
> Signed-off-by: Peter Xu <address@hidden>
Reviewed-by: Dr. David Alan Gilbert <address@hidden>
> ---
> migration/migration.c | 1 +
> migration/migration.h | 1 +
> migration/postcopy-ram.c | 50
> ++++++++++++++++++++++++++++++++++++++++++++----
> migration/savevm.c | 3 +++
> migration/trace-events | 2 ++
> 5 files changed, 53 insertions(+), 4 deletions(-)
>
> diff --git a/migration/migration.c b/migration/migration.c
> index 9a0b5b0..9d93836 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -147,6 +147,7 @@ MigrationIncomingState
> *migration_incoming_get_current(void)
> qemu_mutex_init(&mis_current.rp_mutex);
> qemu_event_init(&mis_current.main_thread_load_event, false);
> qemu_sem_init(&mis_current.postcopy_pause_sem_dst, 0);
> + qemu_sem_init(&mis_current.postcopy_pause_sem_fault, 0);
> once = true;
> }
> return &mis_current;
> diff --git a/migration/migration.h b/migration/migration.h
> index 047872b..574fedd 100644
> --- a/migration/migration.h
> +++ b/migration/migration.h
> @@ -63,6 +63,7 @@ struct MigrationIncomingState {
>
> /* notify PAUSED postcopy incoming migrations to try to continue */
> QemuSemaphore postcopy_pause_sem_dst;
> + QemuSemaphore postcopy_pause_sem_fault;
> };
>
> MigrationIncomingState *migration_incoming_get_current(void);
> diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> index 9ce391d..ba53155 100644
> --- a/migration/postcopy-ram.c
> +++ b/migration/postcopy-ram.c
> @@ -418,6 +418,17 @@ static int ram_block_enable_notify(const char
> *block_name, void *host_addr,
> return 0;
> }
>
> +static bool postcopy_pause_fault_thread(MigrationIncomingState *mis)
> +{
> + trace_postcopy_pause_fault_thread();
> +
> + qemu_sem_wait(&mis->postcopy_pause_sem_fault);
> +
> + trace_postcopy_pause_fault_thread_continued();
> +
> + return true;
> +}
> +
> /*
> * Handle faults detected by the USERFAULT markings
> */
> @@ -465,6 +476,22 @@ static void *postcopy_ram_fault_thread(void *opaque)
> }
> }
>
> + if (!mis->to_src_file) {
> + /*
> + * Possibly someone tells us that the return path is
> + * broken already using the event. We should hold until
> + * the channel is rebuilt.
> + */
> + if (postcopy_pause_fault_thread(mis)) {
> + last_rb = NULL;
> + /* Continue to read the userfaultfd */
> + } else {
> + error_report("%s: paused but don't allow to continue",
> + __func__);
> + break;
> + }
> + }
> +
> ret = read(mis->userfault_fd, &msg, sizeof(msg));
> if (ret != sizeof(msg)) {
> if (errno == EAGAIN) {
> @@ -504,18 +531,33 @@ static void *postcopy_ram_fault_thread(void *opaque)
> qemu_ram_get_idstr(rb),
> rb_offset);
>
> +retry:
> /*
> * Send the request to the source - we want to request one
> * of our host page sizes (which is >= TPS)
> */
> if (rb != last_rb) {
> last_rb = rb;
> - migrate_send_rp_req_pages(mis, qemu_ram_get_idstr(rb),
> - rb_offset, qemu_ram_pagesize(rb));
> + ret = migrate_send_rp_req_pages(mis, qemu_ram_get_idstr(rb),
> + rb_offset,
> qemu_ram_pagesize(rb));
> } else {
> /* Save some space */
> - migrate_send_rp_req_pages(mis, NULL,
> - rb_offset, qemu_ram_pagesize(rb));
> + ret = migrate_send_rp_req_pages(mis, NULL,
> + rb_offset,
> qemu_ram_pagesize(rb));
> + }
> +
> + if (ret) {
> + /* May be network failure, try to wait for recovery */
> + if (ret == -EIO && postcopy_pause_fault_thread(mis)) {
> + /* We got reconnected somehow, try to continue */
> + last_rb = NULL;
> + goto retry;
> + } else {
> + /* This is a unavoidable fault */
> + error_report("%s: migrate_send_rp_req_pages() get %d",
> + __func__, ret);
> + break;
> + }
> }
> }
> trace_postcopy_ram_fault_thread_exit();
> diff --git a/migration/savevm.c b/migration/savevm.c
> index 1f62268..386788d 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -1974,6 +1974,9 @@ static bool
> postcopy_pause_incoming(MigrationIncomingState *mis)
> mis->to_src_file = NULL;
> qemu_mutex_unlock(&mis->rp_mutex);
>
> + /* Notify the fault thread for the invalidated file handle */
> + postcopy_fault_thread_notify(mis);
> +
> while (mis->state == MIGRATION_STATUS_POSTCOPY_PAUSED) {
> qemu_sem_wait(&mis->postcopy_pause_sem_dst);
> }
> diff --git a/migration/trace-events b/migration/trace-events
> index a269eec..dbb4971 100644
> --- a/migration/trace-events
> +++ b/migration/trace-events
> @@ -100,6 +100,8 @@ open_return_path_on_source_continue(void) ""
> postcopy_start(void) ""
> postcopy_pause_return_path(void) ""
> postcopy_pause_return_path_continued(void) ""
> +postcopy_pause_fault_thread(void) ""
> +postcopy_pause_fault_thread_continued(void) ""
> postcopy_pause_continued(void) ""
> postcopy_pause_incoming(void) ""
> postcopy_pause_incoming_continued(void) ""
> --
> 2.7.4
>
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
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