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183 lines
6.7 KiB
183 lines
6.7 KiB
From 7a7e2191f1ac4114380248cbd3c6ab7425250747 Mon Sep 17 00:00:00 2001
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From: Leonardo Bras <leobras@redhat.com>
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Date: Wed, 18 May 2022 02:52:25 -0300
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Subject: [PATCH 23/37] multifd: Implement zero copy write in multifd migration
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(multifd-zero-copy)
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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RH-Author: Leonardo Brás <leobras@redhat.com>
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RH-MergeRequest: 191: MSG_ZEROCOPY + Multifd @ rhel8.7
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RH-Commit: [23/26] 904ce3909cfef62dd84cc7d3c6a3482e7e6f28e9
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RH-Bugzilla: 2072049
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RH-Acked-by: Peter Xu <peterx@redhat.com>
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RH-Acked-by: Daniel P. Berrangé <berrange@redhat.com>
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RH-Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
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Implement zero copy send on nocomp_send_write(), by making use of QIOChannel
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writev + flags & flush interface.
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Change multifd_send_sync_main() so flush_zero_copy() can be called
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after each iteration in order to make sure all dirty pages are sent before
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a new iteration is started. It will also flush at the beginning and at the
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end of migration.
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Also make it return -1 if flush_zero_copy() fails, in order to cancel
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the migration process, and avoid resuming the guest in the target host
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without receiving all current RAM.
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This will work fine on RAM migration because the RAM pages are not usually freed,
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and there is no problem on changing the pages content between writev_zero_copy() and
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the actual sending of the buffer, because this change will dirty the page and
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cause it to be re-sent on a next iteration anyway.
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A lot of locked memory may be needed in order to use multifd migration
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with zero-copy enabled, so disabling the feature should be necessary for
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low-privileged users trying to perform multifd migrations.
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Signed-off-by: Leonardo Bras <leobras@redhat.com>
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Reviewed-by: Peter Xu <peterx@redhat.com>
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Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
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Message-Id: <20220513062836.965425-9-leobras@redhat.com>
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Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
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(cherry picked from commit 5b1d9bab2da4fca3a3caee97c430e5709cb32b7b)
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Signed-off-by: Leonardo Bras <leobras@redhat.com>
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---
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migration/migration.c | 11 ++++++++++-
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migration/multifd.c | 37 +++++++++++++++++++++++++++++++++++--
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migration/multifd.h | 2 ++
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migration/socket.c | 5 +++--
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4 files changed, 50 insertions(+), 5 deletions(-)
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diff --git a/migration/migration.c b/migration/migration.c
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index 8e28f2ee41..5357efd348 100644
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--- a/migration/migration.c
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+++ b/migration/migration.c
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@@ -1471,7 +1471,16 @@ static bool migrate_params_check(MigrationParameters *params, Error **errp)
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error_prepend(errp, "Invalid mapping given for block-bitmap-mapping: ");
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return false;
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}
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-
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+#ifdef CONFIG_LINUX
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+ if (params->zero_copy_send &&
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+ (!migrate_use_multifd() ||
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+ params->multifd_compression != MULTIFD_COMPRESSION_NONE ||
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+ (params->tls_creds && *params->tls_creds))) {
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+ error_setg(errp,
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+ "Zero copy only available for non-compressed non-TLS multifd migration");
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+ return false;
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+ }
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+#endif
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return true;
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}
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diff --git a/migration/multifd.c b/migration/multifd.c
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index 193f70cdba..90ab4c4346 100644
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--- a/migration/multifd.c
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+++ b/migration/multifd.c
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@@ -576,6 +576,7 @@ void multifd_save_cleanup(void)
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int multifd_send_sync_main(QEMUFile *f)
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{
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int i;
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+ bool flush_zero_copy;
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if (!migrate_use_multifd()) {
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return 0;
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@@ -586,6 +587,20 @@ int multifd_send_sync_main(QEMUFile *f)
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return -1;
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}
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}
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+
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+ /*
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+ * When using zero-copy, it's necessary to flush the pages before any of
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+ * the pages can be sent again, so we'll make sure the new version of the
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+ * pages will always arrive _later_ than the old pages.
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+ *
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+ * Currently we achieve this by flushing the zero-page requested writes
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+ * per ram iteration, but in the future we could potentially optimize it
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+ * to be less frequent, e.g. only after we finished one whole scanning of
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+ * all the dirty bitmaps.
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+ */
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+
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+ flush_zero_copy = migrate_use_zero_copy_send();
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+
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for (i = 0; i < migrate_multifd_channels(); i++) {
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MultiFDSendParams *p = &multifd_send_state->params[i];
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@@ -607,6 +622,17 @@ int multifd_send_sync_main(QEMUFile *f)
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ram_counters.transferred += p->packet_len;
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qemu_mutex_unlock(&p->mutex);
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qemu_sem_post(&p->sem);
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+
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+ if (flush_zero_copy && p->c) {
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+ int ret;
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+ Error *err = NULL;
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+
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+ ret = qio_channel_flush(p->c, &err);
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+ if (ret < 0) {
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+ error_report_err(err);
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+ return -1;
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+ }
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+ }
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}
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for (i = 0; i < migrate_multifd_channels(); i++) {
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MultiFDSendParams *p = &multifd_send_state->params[i];
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@@ -691,8 +717,8 @@ static void *multifd_send_thread(void *opaque)
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p->iov[0].iov_base = p->packet;
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}
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- ret = qio_channel_writev_all(p->c, p->iov, p->iovs_num,
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- &local_err);
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+ ret = qio_channel_writev_full_all(p->c, p->iov, p->iovs_num, NULL,
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+ 0, p->write_flags, &local_err);
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if (ret != 0) {
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break;
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}
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@@ -933,6 +959,13 @@ int multifd_save_setup(Error **errp)
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/* We need one extra place for the packet header */
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p->iov = g_new0(struct iovec, page_count + 1);
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p->normal = g_new0(ram_addr_t, page_count);
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+
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+ if (migrate_use_zero_copy_send()) {
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+ p->write_flags = QIO_CHANNEL_WRITE_FLAG_ZERO_COPY;
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+ } else {
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+ p->write_flags = 0;
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+ }
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+
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socket_send_channel_create(multifd_new_send_channel_async, p);
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}
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diff --git a/migration/multifd.h b/migration/multifd.h
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index 92de878155..11d5e273e6 100644
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--- a/migration/multifd.h
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+++ b/migration/multifd.h
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@@ -95,6 +95,8 @@ typedef struct {
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uint32_t packet_len;
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/* pointer to the packet */
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MultiFDPacket_t *packet;
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+ /* multifd flags for sending ram */
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+ int write_flags;
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/* multifd flags for each packet */
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uint32_t flags;
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/* size of the next packet that contains pages */
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diff --git a/migration/socket.c b/migration/socket.c
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index 3754d8f72c..4fd5e85f50 100644
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--- a/migration/socket.c
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+++ b/migration/socket.c
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@@ -79,8 +79,9 @@ static void socket_outgoing_migration(QIOTask *task,
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trace_migration_socket_outgoing_connected(data->hostname);
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- if (migrate_use_zero_copy_send()) {
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- error_setg(&err, "Zero copy send not available in migration");
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+ if (migrate_use_zero_copy_send() &&
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+ !qio_channel_has_feature(sioc, QIO_CHANNEL_FEATURE_WRITE_ZERO_COPY)) {
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+ error_setg(&err, "Zero copy send feature not detected in host kernel");
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}
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out:
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--
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2.35.3
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