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Sun, 15 Sep 2024 09:09:14 -0700 (PDT) From: Hyman Huang To: qemu-devel@nongnu.org Cc: Peter Xu , Fabiano Rosas , Eric Blake , Markus Armbruster , David Hildenbrand , =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= , Paolo Bonzini , yong.huang@smartx.com Subject: [PATCH v1 5/7] migration: Support background dirty bitmap sync and throttle Date: Mon, 16 Sep 2024 00:08:48 +0800 Message-Id: X-Mailer: git-send-email 2.39.1 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=2607:f8b0:4864:20::436; envelope-from=yong.huang@smartx.com; helo=mail-pf1-x436.google.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=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: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @smartx-com.20230601.gappssmtp.com) X-ZM-MESSAGEID: 1726416603253116600 Content-Type: text/plain; charset="utf-8" When VM is configured with huge memory, the current throttle logic doesn't look like to scale, because migration_trigger_throttle() is only called for each iteration, so it won't be invoked for a long time if one iteration can take a long time. The background sync and throttle aim to fix the above issue by synchronizing the remote dirty bitmap and triggering the throttle once detect that iteration lasts a long time. This is a trade-off between synchronization overhead and CPU throttle impact. Signed-off-by: Hyman Huang --- migration/migration.c | 12 +++++++++++ tests/qtest/migration-test.c | 39 ++++++++++++++++++++++++++++++++++++ 2 files changed, 51 insertions(+) diff --git a/migration/migration.c b/migration/migration.c index 055d527ff6..af8b22fa15 100644 --- a/migration/migration.c +++ b/migration/migration.c @@ -1416,6 +1416,7 @@ static void migrate_fd_cleanup(MigrationState *s) =20 trace_migrate_fd_cleanup(); bql_unlock(); + migration_background_sync_cleanup(); if (s->migration_thread_running) { qemu_thread_join(&s->thread); s->migration_thread_running =3D false; @@ -3263,6 +3264,7 @@ static MigIterateState migration_iteration_run(Migrat= ionState *s) =20 if ((!pending_size || pending_size < s->threshold_size) && can_switcho= ver) { trace_migration_thread_low_pending(pending_size); + migration_background_sync_cleanup(); migration_completion(s); return MIG_ITERATE_BREAK; } @@ -3508,6 +3510,16 @@ static void *migration_thread(void *opaque) ret =3D qemu_savevm_state_setup(s->to_dst_file, &local_err); bql_unlock(); =20 + if (!migrate_dirty_limit()) { + /* + * Initiate the background sync watcher in order to guarantee + * that the CPU throttling acts appropriately. Dirty Limit + * doesn't use CPU throttle to make guest down, so ignore that + * case. + */ + migration_background_sync_setup(); + } + qemu_savevm_wait_unplug(s, MIGRATION_STATUS_SETUP, MIGRATION_STATUS_ACTIVE); =20 diff --git a/tests/qtest/migration-test.c b/tests/qtest/migration-test.c index b796a90cad..e0e94d26be 100644 --- a/tests/qtest/migration-test.c +++ b/tests/qtest/migration-test.c @@ -281,6 +281,11 @@ static uint64_t get_migration_pass(QTestState *who) return read_ram_property_int(who, "iteration-count"); } =20 +static uint64_t get_dirty_sync_count(QTestState *who) +{ + return read_ram_property_int(who, "dirty-sync-count"); +} + static void read_blocktime(QTestState *who) { QDict *rsp_return; @@ -468,6 +473,12 @@ static void migrate_ensure_converge(QTestState *who) migrate_set_parameter_int(who, "downtime-limit", 30 * 1000); } =20 +static void migrate_ensure_iteration_last_long(QTestState *who) +{ + /* Set 10Byte/s bandwidth limit to make the iteration last long enough= */ + migrate_set_parameter_int(who, "max-bandwidth", 10); +} + /* * Our goal is to ensure that we run a single full migration * iteration, and also dirty memory, ensuring that at least @@ -2791,6 +2802,10 @@ static void test_migrate_auto_converge(void) * so we need to decrease a bandwidth. */ const int64_t init_pct =3D 5, inc_pct =3D 25, max_pct =3D 95; + uint64_t prev_iter_cnt =3D 0, iter_cnt; + uint64_t iter_cnt_changes =3D 0; + uint64_t prev_dirty_sync_cnt =3D 0, dirty_sync_cnt; + uint64_t dirty_sync_cnt_changes =3D 0; =20 if (test_migrate_start(&from, &to, uri, &args)) { return; @@ -2827,6 +2842,30 @@ static void test_migrate_auto_converge(void) } while (true); /* The first percentage of throttling should be at least init_pct */ g_assert_cmpint(percentage, >=3D, init_pct); + + /* Make sure the iteration take a long time enough */ + migrate_ensure_iteration_last_long(from); + + /* + * End the loop when the dirty sync count or iteration count changes. + */ + while (iter_cnt_changes < 2 && dirty_sync_cnt_changes < 2) { + usleep(1000 * 1000); + iter_cnt =3D get_migration_pass(from); + iter_cnt_changes +=3D (iter_cnt !=3D prev_iter_cnt); + prev_iter_cnt =3D iter_cnt; + + dirty_sync_cnt =3D get_dirty_sync_count(from); + dirty_sync_cnt_changes +=3D (dirty_sync_cnt !=3D prev_dirty_sync_c= nt); + prev_dirty_sync_cnt =3D dirty_sync_cnt; + } + + /* + * The dirty sync count must have changed because we are in the same + * iteration. + */ + g_assert_cmpint(iter_cnt_changes , < , dirty_sync_cnt_changes); + /* Now, when we tested that throttling works, let it converge */ migrate_ensure_converge(from); =20 --=20 2.39.1