{"id":2225923,"url":"http://patchwork.ozlabs.org/api/patches/2225923/?format=json","web_url":"http://patchwork.ozlabs.org/project/qemu-devel/patch/20260421202110.306051-11-peterx@redhat.com/","project":{"id":14,"url":"http://patchwork.ozlabs.org/api/projects/14/?format=json","name":"QEMU Development","link_name":"qemu-devel","list_id":"qemu-devel.nongnu.org","list_email":"qemu-devel@nongnu.org","web_url":"","scm_url":"","webscm_url":"","list_archive_url":"","list_archive_url_format":"","commit_url_format":""},"msgid":"<20260421202110.306051-11-peterx@redhat.com>","list_archive_url":null,"date":"2026-04-21T20:21:04","name":"[v2,10/16] migration: Introduce a helper to return switchover bw estimate","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"40910d22baa7354680a125e81bcdbdcb5281a2b6","submitter":{"id":67717,"url":"http://patchwork.ozlabs.org/api/people/67717/?format=json","name":"Peter Xu","email":"peterx@redhat.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/qemu-devel/patch/20260421202110.306051-11-peterx@redhat.com/mbox/","series":[{"id":500889,"url":"http://patchwork.ozlabs.org/api/series/500889/?format=json","web_url":"http://patchwork.ozlabs.org/project/qemu-devel/list/?series=500889","date":"2026-04-21T20:20:55","name":"migration/vfio: Fix a few issues on API misuse or statistic reports","version":2,"mbox":"http://patchwork.ozlabs.org/series/500889/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2225923/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2225923/checks/","tags":{},"related":[],"headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=h6iok2/v;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=google header.b=kNofL9P3;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; 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Szmigiero\" ,\n Juraj Marcin ","Subject":"[PATCH v2 10/16] migration: Introduce a helper to return switchover\n bw estimate","Date":"Tue, 21 Apr 2026 16:21:04 -0400","Message-ID":"<20260421202110.306051-11-peterx@redhat.com>","X-Mailer":"git-send-email 2.53.0","In-Reply-To":"<20260421202110.306051-1-peterx@redhat.com>","References":"<20260421202110.306051-1-peterx@redhat.com>","MIME-Version":"1.0","Content-Transfer-Encoding":"8bit","Received-SPF":"pass client-ip=170.10.129.124; envelope-from=peterx@redhat.com;\n helo=us-smtp-delivery-124.mimecast.com","X-Spam_score_int":"-20","X-Spam_score":"-2.1","X-Spam_bar":"--","X-Spam_report":"(-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001,\n DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1,\n RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001,\n SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no","X-Spam_action":"no action","X-BeenThere":"qemu-devel@nongnu.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"qemu development ","List-Unsubscribe":",\n ","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n ","Errors-To":"qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org","Sender":"qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org"},"content":"Add a helper migration_get_switchover_bw() to return an estimate of\nswitchover bandwidth. Use it to simplify the current code.\n\nThis will be used in later to remove expected_downtime.\n\nWhen at it, remove two qatomic_read() to shrink the lines because atomic\nops are not needed when it's always the same thread who does the updates.\n\nReviewed-by: Juraj Marcin \nSigned-off-by: Peter Xu \n---\n migration/migration.c | 48 +++++++++++++++++++++----------------------\n 1 file changed, 24 insertions(+), 24 deletions(-)","diff":"diff --git a/migration/migration.c b/migration/migration.c\nindex e3f82baaac..caa1d13130 100644\n--- a/migration/migration.c\n+++ b/migration/migration.c\n@@ -984,6 +984,21 @@ void migrate_send_rp_resume_ack(MigrationIncomingState *mis, uint32_t value)\n migrate_send_rp_message(mis, MIG_RP_MSG_RESUME_ACK, sizeof(buf), &buf);\n }\n \n+/*\n+ * Returns the estimated switchover bandwidth (unit: bytes / seconds)\n+ */\n+static double migration_get_switchover_bw(MigrationState *s)\n+{\n+ uint64_t switchover_bw = migrate_avail_switchover_bandwidth();\n+\n+ if (switchover_bw) {\n+ /* If user specified, prioritize this value and don't estimate */\n+ return (double)switchover_bw;\n+ }\n+\n+ return s->mbps / 8 * 1000 * 1000;\n+}\n+\n bool migration_is_running(void)\n {\n MigrationState *s = current_migration;\n@@ -3126,37 +3141,22 @@ static void migration_update_counters(MigrationState *s,\n {\n uint64_t transferred, transferred_pages, time_spent;\n uint64_t current_bytes; /* bytes transferred since the beginning */\n- uint64_t switchover_bw;\n- /* Expected bandwidth when switching over to destination QEMU */\n- double expected_bw_per_ms;\n- double bandwidth;\n+ double switchover_bw_per_ms;\n \n if (current_time < s->iteration_start_time + BUFFER_DELAY) {\n return;\n }\n \n- switchover_bw = migrate_avail_switchover_bandwidth();\n current_bytes = migration_transferred_bytes();\n transferred = current_bytes - s->iteration_initial_bytes;\n time_spent = current_time - s->iteration_start_time;\n- bandwidth = (double)transferred / time_spent;\n-\n- if (switchover_bw) {\n- /*\n- * If the user specified a switchover bandwidth, let's trust the\n- * user so that can be more accurate than what we estimated.\n- */\n- expected_bw_per_ms = (double)switchover_bw / 1000;\n- } else {\n- /* If the user doesn't specify bandwidth, we use the estimated */\n- expected_bw_per_ms = bandwidth;\n- }\n-\n- s->threshold_size = expected_bw_per_ms * migrate_downtime_limit();\n-\n s->mbps = (((double) transferred * 8.0) /\n ((double) time_spent / 1000.0)) / 1000.0 / 1000.0;\n \n+ /* NOTE: only update this after bandwidth (s->mbps) updated */\n+ switchover_bw_per_ms = migration_get_switchover_bw(s) / 1000;\n+ s->threshold_size = switchover_bw_per_ms * migrate_downtime_limit();\n+\n transferred_pages = ram_get_total_transferred_pages() -\n s->iteration_initial_pages;\n s->pages_per_second = (double) transferred_pages /\n@@ -3166,10 +3166,9 @@ static void migration_update_counters(MigrationState *s,\n * if we haven't sent anything, we don't want to\n * recalculate. 10000 is a small enough number for our purposes\n */\n- if (qatomic_read(&mig_stats.dirty_pages_rate) &&\n- transferred > 10000) {\n+ if (mig_stats.dirty_pages_rate && transferred > 10000) {\n s->expected_downtime =\n- qatomic_read(&mig_stats.dirty_bytes_last_sync) / expected_bw_per_ms;\n+ mig_stats.dirty_bytes_last_sync / switchover_bw_per_ms;\n }\n \n migration_rate_reset();\n@@ -3178,7 +3177,8 @@ static void migration_update_counters(MigrationState *s,\n \n trace_migrate_transferred(transferred, time_spent,\n /* Both in unit bytes/ms */\n- bandwidth, switchover_bw / 1000,\n+ (uint64_t)s->mbps,\n+ (uint64_t)switchover_bw_per_ms,\n s->threshold_size);\n }\n \n","prefixes":["v2","10/16"]}