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Re: [Qemu-devel] [PATCH v3 1/2] migration: allow to prioritize save stat
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH v3 1/2] migration: allow to prioritize save state entries |
Date: |
Fri, 6 Jan 2017 13:19:05 +0000 |
User-agent: |
Mutt/1.7.1 (2016-10-04) |
* Peter Xu (address@hidden) wrote:
> During migration, save state entries are saved/loaded without a specific
> order - we just traverse the savevm_state.handlers list and do it one by
> one. This might not be enough.
>
> There are requirements that we need to load specific device's vmstate
> first before others. For example, VT-d IOMMU contains DMA address
> remapping information, which is required by all the PCI devices to do
> address translations. We need to make sure IOMMU's device state is
> loaded before the rest of the PCI devices, so that DMA address
> translation can work properly.
>
> This patch provide a VMStateDescription.priority value to allow specify
> the priority of the saved states. The loadvm operation will be done with
> those devices with higher vmsd priority.
>
> Before this patch, we are possibly achieving the ordering requirement by
> an assumption that the ordering will be the same with the ordering that
> objects are created. A better way is to mark it out explicitly in the
> VMStateDescription table, like what this patch does.
>
> Current ordering logic is still naive and slow, but after all that's not
> a critical path so IMO it's a workable solution for now.
So I think this is quite simple and makes sense; all existing stuff
says in the same order, and things of equal priority get added in the
same order. I suspect if we start doing it to lots of devices
we'll come up with more complex requirements.
> Signed-off-by: Peter Xu <address@hidden>
Reviewed-by: Dr. David Alan Gilbert <address@hidden>
> ---
> include/migration/vmstate.h | 6 ++++++
> migration/savevm.c | 34 ++++++++++++++++++++++++++++++----
> 2 files changed, 36 insertions(+), 4 deletions(-)
>
> diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
> index 1638ee5..1a22887 100644
> --- a/include/migration/vmstate.h
> +++ b/include/migration/vmstate.h
> @@ -186,6 +186,11 @@ enum VMStateFlags {
> VMS_MULTIPLY_ELEMENTS = 0x4000,
> };
>
> +typedef enum {
> + MIG_PRI_DEFAULT = 0,
> + MIG_PRI_MAX,
> +} MigrationPriority;
> +
> typedef struct {
> const char *name;
> size_t offset;
> @@ -207,6 +212,7 @@ struct VMStateDescription {
> int version_id;
> int minimum_version_id;
> int minimum_version_id_old;
> + MigrationPriority priority;
> LoadStateHandler *load_state_old;
> int (*pre_load)(void *opaque);
> int (*post_load)(void *opaque, int version_id);
> diff --git a/migration/savevm.c b/migration/savevm.c
> index 0363372..f9c06e9 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -532,6 +532,34 @@ static int calculate_compat_instance_id(const char
> *idstr)
> return instance_id;
> }
>
> +static inline MigrationPriority save_state_priority(SaveStateEntry *se)
> +{
> + if (se->vmsd) {
> + return se->vmsd->priority;
> + }
> + return MIG_PRI_DEFAULT;
> +}
> +
> +static void savevm_state_handler_insert(SaveStateEntry *nse)
> +{
> + MigrationPriority priority = save_state_priority(nse);
> + SaveStateEntry *se;
> +
> + assert(priority <= MIG_PRI_MAX);
> +
> + QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
> + if (save_state_priority(se) < priority) {
> + break;
> + }
> + }
> +
> + if (se) {
> + QTAILQ_INSERT_BEFORE(se, nse, entry);
> + } else {
> + QTAILQ_INSERT_TAIL(&savevm_state.handlers, nse, entry);
> + }
> +}
> +
> /* TODO: Individual devices generally have very little idea about the rest
> of the system, so instance_id should be removed/replaced.
> Meanwhile pass -1 as instance_id if you do not already have a clearly
> @@ -578,8 +606,7 @@ int register_savevm_live(DeviceState *dev,
> se->instance_id = instance_id;
> }
> assert(!se->compat || se->instance_id == 0);
> - /* add at the end of list */
> - QTAILQ_INSERT_TAIL(&savevm_state.handlers, se, entry);
> + savevm_state_handler_insert(se);
> return 0;
> }
>
> @@ -662,8 +689,7 @@ int vmstate_register_with_alias_id(DeviceState *dev, int
> instance_id,
> se->instance_id = instance_id;
> }
> assert(!se->compat || se->instance_id == 0);
> - /* add at the end of list */
> - QTAILQ_INSERT_TAIL(&savevm_state.handlers, se, entry);
> + savevm_state_handler_insert(se);
> return 0;
> }
>
> --
> 2.7.4
>
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK