On Mon, Feb 21, 2022 at 06:39:36PM +0000, Dr. David Alan Gilbert wrote:
> * Peter Xu (pet...@redhat.com) wrote:
> > Create a new socket for postcopy to be prepared to send postcopy requested
> > pages via this specific channel, so as to not get blocked by precopy pages.
> >
> > A new thread is also created on dest qemu to receive data from this new
> > channel
> > based on the ram_load_postcopy() routine.
> >
> > The ram_load_postcopy(POSTCOPY) branch and the thread has not started to
> > function, and that'll be done in follow up patches.
> >
> > Cleanup the new sockets on both src/dst QEMUs, meanwhile look after the new
> > thread too to make sure it'll be recycled properly.
> >
> > Signed-off-by: Peter Xu <pet...@redhat.com>
> > ---
> > migration/migration.c | 62 ++++++++++++++++++++++++----
> > migration/migration.h | 8 ++++
> > migration/postcopy-ram.c | 88 ++++++++++++++++++++++++++++++++++++++--
> > migration/postcopy-ram.h | 10 +++++
> > migration/ram.c | 25 ++++++++----
> > migration/ram.h | 4 +-
> > migration/socket.c | 22 +++++++++-
> > migration/socket.h | 1 +
> > migration/trace-events | 3 ++
> > 9 files changed, 203 insertions(+), 20 deletions(-)
> >
> > diff --git a/migration/migration.c b/migration/migration.c
> > index 4c22bad304..3d7f897b72 100644
> > --- a/migration/migration.c
> > +++ b/migration/migration.c
> > @@ -321,6 +321,12 @@ void migration_incoming_state_destroy(void)
> > mis->page_requested = NULL;
> > }
> >
> > + if (mis->postcopy_qemufile_dst) {
> > +
> > migration_ioc_unregister_yank_from_file(mis->postcopy_qemufile_dst);
> > + qemu_fclose(mis->postcopy_qemufile_dst);
> > + mis->postcopy_qemufile_dst = NULL;
> > + }
> > +
> > yank_unregister_instance(MIGRATION_YANK_INSTANCE);
> > }
> >
> > @@ -714,15 +720,21 @@ void migration_fd_process_incoming(QEMUFile *f, Error
> > **errp)
> > migration_incoming_process();
> > }
> >
> > +static bool migration_needs_multiple_sockets(void)
> > +{
> > + return migrate_use_multifd() || migrate_postcopy_preempt();
> > +}
> > +
> > void migration_ioc_process_incoming(QIOChannel *ioc, Error **errp)
> > {
> > MigrationIncomingState *mis = migration_incoming_get_current();
> > Error *local_err = NULL;
> > bool start_migration;
> > + QEMUFile *f;
> >
> > if (!mis->from_src_file) {
> > /* The first connection (multifd may have multiple) */
> > - QEMUFile *f = qemu_fopen_channel_input(ioc);
> > + f = qemu_fopen_channel_input(ioc);
> >
> > if (!migration_incoming_setup(f, errp)) {
> > return;
> > @@ -730,13 +742,18 @@ void migration_ioc_process_incoming(QIOChannel *ioc,
> > Error **errp)
> >
> > /*
> > * Common migration only needs one channel, so we can start
> > - * right now. Multifd needs more than one channel, we wait.
> > + * right now. Some features need more than one channel, we wait.
> > */
> > - start_migration = !migrate_use_multifd();
> > + start_migration = !migration_needs_multiple_sockets();
> > } else {
> > /* Multiple connections */
> > - assert(migrate_use_multifd());
> > - start_migration = multifd_recv_new_channel(ioc, &local_err);
> > + assert(migration_needs_multiple_sockets());
> > + if (migrate_use_multifd()) {
> > + start_migration = multifd_recv_new_channel(ioc, &local_err);
> > + } else if (migrate_postcopy_preempt()) {
> > + f = qemu_fopen_channel_input(ioc);
> > + start_migration = postcopy_preempt_new_channel(mis, f);
> > + }
> > if (local_err) {
> > error_propagate(errp, local_err);
> > return;
> > @@ -761,11 +778,20 @@ void migration_ioc_process_incoming(QIOChannel *ioc,
> > Error **errp)
> > bool migration_has_all_channels(void)
> > {
> > MigrationIncomingState *mis = migration_incoming_get_current();
> > - bool all_channels;
> >
> > - all_channels = multifd_recv_all_channels_created();
> > + if (!mis->from_src_file) {
> > + return false;
> > + }
> > +
> > + if (migrate_use_multifd()) {
> > + return multifd_recv_all_channels_created();
> > + }
> > +
> > + if (migrate_postcopy_preempt()) {
> > + return mis->postcopy_qemufile_dst != NULL;
> > + }
> >
> > - return all_channels && mis->from_src_file != NULL;
> > + return true;
> > }
> >
> > /*
> > @@ -1858,6 +1884,12 @@ static void migrate_fd_cleanup(MigrationState *s)
> > qemu_fclose(tmp);
> > }
> >
> > + if (s->postcopy_qemufile_src) {
> > + migration_ioc_unregister_yank_from_file(s->postcopy_qemufile_src);
> > + qemu_fclose(s->postcopy_qemufile_src);
> > + s->postcopy_qemufile_src = NULL;
> > + }
> > +
> > assert(!migration_is_active(s));
> >
> > if (s->state == MIGRATION_STATUS_CANCELLING) {
> > @@ -3233,6 +3265,11 @@ static void migration_completion(MigrationState *s)
> > qemu_savevm_state_complete_postcopy(s->to_dst_file);
> > qemu_mutex_unlock_iothread();
> >
> > + /* Shutdown the postcopy fast path thread */
> > + if (migrate_postcopy_preempt()) {
> > + postcopy_preempt_shutdown_file(s);
> > + }
> > +
> > trace_migration_completion_postcopy_end_after_complete();
> > } else {
> > goto fail;
> > @@ -4120,6 +4157,15 @@ void migrate_fd_connect(MigrationState *s, Error
> > *error_in)
> > }
> > }
> >
> > + /* This needs to be done before resuming a postcopy */
> > + if (postcopy_preempt_setup(s, &local_err)) {
> > + error_report_err(local_err);
> > + migrate_set_state(&s->state, MIGRATION_STATUS_SETUP,
> > + MIGRATION_STATUS_FAILED);
> > + migrate_fd_cleanup(s);
> > + return;
> > + }
> > +
> > if (resume) {
> > /* Wakeup the main migration thread to do the recovery */
> > migrate_set_state(&s->state, MIGRATION_STATUS_POSTCOPY_PAUSED,
> > diff --git a/migration/migration.h b/migration/migration.h
> > index af4bcb19c2..caa910d956 100644
> > --- a/migration/migration.h
> > +++ b/migration/migration.h
> > @@ -23,6 +23,7 @@
> > #include "io/channel-buffer.h"
> > #include "net/announce.h"
> > #include "qom/object.h"
> > +#include "postcopy-ram.h"
> >
> > struct PostcopyBlocktimeContext;
> >
> > @@ -112,6 +113,11 @@ struct MigrationIncomingState {
> > * enabled.
> > */
> > unsigned int postcopy_channels;
> > + /* QEMUFile for postcopy only; it'll be handled by a separate thread */
> > + QEMUFile *postcopy_qemufile_dst;
> > + /* Postcopy priority thread is used to receive postcopy requested
> > pages */
> > + QemuThread postcopy_prio_thread;
> > + bool postcopy_prio_thread_created;
> > /*
> > * An array of temp host huge pages to be used, one for each postcopy
> > * channel.
> > @@ -192,6 +198,8 @@ struct MigrationState {
> > QEMUBH *cleanup_bh;
> > /* Protected by qemu_file_lock */
> > QEMUFile *to_dst_file;
> > + /* Postcopy specific transfer channel */
> > + QEMUFile *postcopy_qemufile_src;
> > QIOChannelBuffer *bioc;
> > /*
> > * Protects to_dst_file/from_dst_file pointers. We need to make sure
> > we
> > diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> > index 738cc55fa6..30eddaacd1 100644
> > --- a/migration/postcopy-ram.c
> > +++ b/migration/postcopy-ram.c
> > @@ -32,6 +32,9 @@
> > #include "trace.h"
> > #include "hw/boards.h"
> > #include "exec/ramblock.h"
> > +#include "socket.h"
> > +#include "qemu-file-channel.h"
> > +#include "yank_functions.h"
> >
> > /* Arbitrary limit on size of each discard command,
> > * keeps them around ~200 bytes
> > @@ -566,6 +569,11 @@ int
> > postcopy_ram_incoming_cleanup(MigrationIncomingState *mis)
> > {
> > trace_postcopy_ram_incoming_cleanup_entry();
> >
> > + if (mis->postcopy_prio_thread_created) {
> > + qemu_thread_join(&mis->postcopy_prio_thread);
> > + mis->postcopy_prio_thread_created = false;
> > + }
> > +
> > if (mis->have_fault_thread) {
> > Error *local_err = NULL;
> >
> > @@ -1101,8 +1109,13 @@ static int
> > postcopy_temp_pages_setup(MigrationIncomingState *mis)
> > int err, i, channels;
> > void *temp_page;
> >
> > - /* TODO: will be boosted when enable postcopy preemption */
> > - mis->postcopy_channels = 1;
> > + if (migrate_postcopy_preempt()) {
> > + /* If preemption enabled, need extra channel for urgent requests */
> > + mis->postcopy_channels = RAM_CHANNEL_MAX;
> > + } else {
> > + /* Both precopy/postcopy on the same channel */
> > + mis->postcopy_channels = 1;
> > + }
> >
> > channels = mis->postcopy_channels;
> > mis->postcopy_tmp_pages = g_malloc0_n(sizeof(PostcopyTmpPage),
> > channels);
> > @@ -1169,7 +1182,7 @@ int
> > postcopy_ram_incoming_setup(MigrationIncomingState *mis)
> > return -1;
> > }
> >
> > - postcopy_thread_create(mis, &mis->fault_thread, "postcopy/fault",
> > + postcopy_thread_create(mis, &mis->fault_thread, "qemu/fault-default",
>
> That name is still too long; I'd lose the 'qemu/'
Sure.
>
> > postcopy_ram_fault_thread,
> > QEMU_THREAD_JOINABLE);
> > mis->have_fault_thread = true;
> >
> > @@ -1184,6 +1197,16 @@ int
> > postcopy_ram_incoming_setup(MigrationIncomingState *mis)
> > return -1;
> > }
> >
> > + if (migrate_postcopy_preempt()) {
> > + /*
> > + * This thread needs to be created after the temp pages because
> > it'll fetch
> > + * RAM_CHANNEL_POSTCOPY PostcopyTmpPage immediately.
> > + */
> > + postcopy_thread_create(mis, &mis->postcopy_prio_thread,
> > "qemu/fault-fast",
>
> and that one.
OK.
>
> > + postcopy_preempt_thread,
> > QEMU_THREAD_JOINABLE);
> > + mis->postcopy_prio_thread_created = true;
> > + }
> > +
> > trace_postcopy_ram_enable_notify();
> >
> > return 0;
> > @@ -1513,3 +1536,62 @@ void postcopy_unregister_shared_ufd(struct
> > PostCopyFD *pcfd)
> > }
> > }
> > }
> > +
> > +bool postcopy_preempt_new_channel(MigrationIncomingState *mis, QEMUFile
> > *file)
> > +{
> > + mis->postcopy_qemufile_dst = file;
> > +
> > + trace_postcopy_preempt_new_channel();
> > +
> > + /* Start the migration immediately */
> > + return true;
> > +}
> > +
> > +int postcopy_preempt_setup(MigrationState *s, Error **errp)
> > +{
> > + QIOChannel *ioc;
> > +
> > + if (!migrate_postcopy_preempt()) {
> > + return 0;
> > + }
> > +
> > + if (!migrate_multi_channels_is_allowed()) {
> > + error_setg(errp, "Postcopy preempt is not supported as current "
> > + "migration stream does not support multi-channels.");
> > + return -1;
> > + }
> > +
> > + ioc = socket_send_channel_create_sync(errp);
>
> How do we get away with doing this sync here, but have to use async for
> multifd?
Ah right.. I think both will work? But async (as what multifd is doing)
is definitely more elegant because synced version can block the main thread
for unexpected times.
I'll add a new patch to support async channel creations (assuming that's
better than squashing the change).
--
Peter Xu
