[v3 0/6] dirtylimit: miscellaneous patches

[v3 0/6] dirtylimit: miscellaneous patches

[Hyman Huang]

v3:
- do nothing but rebase on master

v2:
- rebase on master.
- fix the document typo.

v1:
This is a miscellaneous patchset for dirtylimit that contains
the following parts:

1. dirtylimit module: fix for a race situation and
   replace usleep by g_usleep.
2. migration test: add dirtylimit test case.
3. guestperf for migration: add support for dirtylimit migration.
4. docs for migration: add dirtylimit section. 

Please review, thanks.

Regards,

Hyman Huang (6):
  system/dirtylimit: Fix a race situation
  system/dirtylimit: Drop the reduplicative check
  tests: Add migration dirty-limit capability test
  tests/migration: Introduce dirty-ring-size option into guestperf
  tests/migration: Introduce dirty-limit into guestperf
  docs/migration: Add the dirty limit section

 docs/devel/migration.rst                |  71 ++++++++++
 system/dirtylimit.c                     |  24 ++--
 tests/migration/guestperf/comparison.py |  23 ++++
 tests/migration/guestperf/engine.py     |  23 +++-
 tests/migration/guestperf/hardware.py   |   8 +-
 tests/migration/guestperf/progress.py   |  16 ++-
 tests/migration/guestperf/scenario.py   |  11 +-
 tests/migration/guestperf/shell.py      |  24 +++-
 tests/qtest/migration-test.c            | 164 ++++++++++++++++++++++++
 9 files changed, 346 insertions(+), 18 deletions(-)

-- 
2.39.1

[v3 1/6] system/dirtylimit: Fix a race situation

[Hyman Huang]

Fix a race situation for global variable dirtylimit_state.

Also, replace usleep by g_usleep to increase platform
accessibility to the sleep function.

Signed-off-by: Hyman Huang <yong.huang@smartx.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Message-Id: <f25558b3d94083ce6909da5b5cfb922ae5935626.1697815117.git.yong.huang@smartx.com>
---
 system/dirtylimit.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/system/dirtylimit.c b/system/dirtylimit.c
index fa959d7743..3666c4cb7c 100644
--- a/system/dirtylimit.c
+++ b/system/dirtylimit.c
@@ -411,12 +411,20 @@ void dirtylimit_set_all(uint64_t quota,
 
 void dirtylimit_vcpu_execute(CPUState *cpu)
 {
-    if (dirtylimit_in_service() &&
-        dirtylimit_vcpu_get_state(cpu->cpu_index)->enabled &&
-        cpu->throttle_us_per_full) {
-        trace_dirtylimit_vcpu_execute(cpu->cpu_index,
-                cpu->throttle_us_per_full);
-        usleep(cpu->throttle_us_per_full);
+    if (cpu->throttle_us_per_full) {
+        dirtylimit_state_lock();
+
+        if (dirtylimit_in_service() &&
+            dirtylimit_vcpu_get_state(cpu->cpu_index)->enabled) {
+            dirtylimit_state_unlock();
+            trace_dirtylimit_vcpu_execute(cpu->cpu_index,
+                    cpu->throttle_us_per_full);
+
+            g_usleep(cpu->throttle_us_per_full);
+            return;
+        }
+
+        dirtylimit_state_unlock();
     }
 }
 
-- 
2.39.1

Re: [v3 1/6] system/dirtylimit: Fix a race situation

[Juan Quintela]

Hyman Huang <yong.huang@smartx.com> wrote:
> Fix a race situation for global variable dirtylimit_state.
>
> Also, replace usleep by g_usleep to increase platform
> accessibility to the sleep function.
>
> Signed-off-by: Hyman Huang <yong.huang@smartx.com>
> Reviewed-by: Fabiano Rosas <farosas@suse.de>
> Message-Id: <f25558b3d94083ce6909da5b5cfb922ae5935626.1697815117.git.yong.huang@smartx.com>

Reviewed-by: Juan Quintela <quintela@redhat.com>

queued.

[v3 2/6] system/dirtylimit: Drop the reduplicative check

[Hyman Huang]

Checking if dirty limit is in service is done by the
dirtylimit_query_all function, drop the reduplicative
check in the qmp_query_vcpu_dirty_limit function.

Signed-off-by: Hyman Huang <yong.huang@smartx.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Message-Id: <31384f768279027560ab952ebc2bbff1ddb62531.1697815117.git.yong.huang@smartx.com>
---
 system/dirtylimit.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/system/dirtylimit.c b/system/dirtylimit.c
index 3666c4cb7c..495c7a7082 100644
--- a/system/dirtylimit.c
+++ b/system/dirtylimit.c
@@ -652,10 +652,6 @@ static struct DirtyLimitInfoList *dirtylimit_query_all(void)
 
 struct DirtyLimitInfoList *qmp_query_vcpu_dirty_limit(Error **errp)
 {
-    if (!dirtylimit_in_service()) {
-        return NULL;
-    }
-
     return dirtylimit_query_all();
 }
 
-- 
2.39.1

Re: [v3 2/6] system/dirtylimit: Drop the reduplicative check

[Juan Quintela]

Hyman Huang <yong.huang@smartx.com> wrote:
> Checking if dirty limit is in service is done by the
> dirtylimit_query_all function, drop the reduplicative
> check in the qmp_query_vcpu_dirty_limit function.
>
> Signed-off-by: Hyman Huang <yong.huang@smartx.com>
> Reviewed-by: Fabiano Rosas <farosas@suse.de>
> Message-Id: <31384f768279027560ab952ebc2bbff1ddb62531.1697815117.git.yong.huang@smartx.com>

Reviewed-by: Juan Quintela <quintela@redhat.com>
queued.

[v3 3/6] tests: Add migration dirty-limit capability test

[Hyman Huang]

Add migration dirty-limit capability test if kernel support
dirty ring.

Migration dirty-limit capability introduce dirty limit
capability, two parameters: x-vcpu-dirty-limit-period and
vcpu-dirty-limit are introduced to implement the live
migration with dirty limit.

The test case does the following things:
1. start src, dst vm and enable dirty-limit capability
2. start migrate and set cancel it to check if dirty limit
   stop working.
3. restart dst vm
4. start migrate and enable dirty-limit capability
5. check if migration satisfy the convergence condition
   during pre-switchover phase.

Note that this test case involves many passes, so it runs
in slow mode only.

Signed-off-by: Hyman Huang <yong.huang@smartx.com>
Acked-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Message-Id: <a05e931ed147696bd5924e0582db67a734547a3f.1697815117.git.yong.huang@smartx.com>
---
 tests/qtest/migration-test.c | 164 +++++++++++++++++++++++++++++++++++
 1 file changed, 164 insertions(+)

diff --git a/tests/qtest/migration-test.c b/tests/qtest/migration-test.c
index bc70a14642..0693078b07 100644
--- a/tests/qtest/migration-test.c
+++ b/tests/qtest/migration-test.c
@@ -2968,6 +2968,166 @@ static void test_vcpu_dirty_limit(void)
     dirtylimit_stop_vm(vm);
 }
 
+static void migrate_dirty_limit_wait_showup(QTestState *from,
+                                            const int64_t period,
+                                            const int64_t value)
+{
+    /* Enable dirty limit capability */
+    migrate_set_capability(from, "dirty-limit", true);
+
+    /* Set dirty limit parameters */
+    migrate_set_parameter_int(from, "x-vcpu-dirty-limit-period", period);
+    migrate_set_parameter_int(from, "vcpu-dirty-limit", value);
+
+    /* Make sure migrate can't converge */
+    migrate_ensure_non_converge(from);
+
+    /* To check limit rate after precopy */
+    migrate_set_capability(from, "pause-before-switchover", true);
+
+    /* Wait for the serial output from the source */
+    wait_for_serial("src_serial");
+}
+
+/*
+ * This test does:
+ *  source                          destination
+ *  start vm
+ *                                  start incoming vm
+ *  migrate
+ *  wait dirty limit to begin
+ *  cancel migrate
+ *  cancellation check
+ *                                  restart incoming vm
+ *  migrate
+ *  wait dirty limit to begin
+ *  wait pre-switchover event
+ *  convergence condition check
+ *
+ * And see if dirty limit migration works correctly.
+ * This test case involves many passes, so it runs in slow mode only.
+ */
+static void test_migrate_dirty_limit(void)
+{
+    g_autofree char *uri = g_strdup_printf("unix:%s/migsocket", tmpfs);
+    QTestState *from, *to;
+    int64_t remaining;
+    uint64_t throttle_us_per_full;
+    /*
+     * We want the test to be stable and as fast as possible.
+     * E.g., with 1Gb/s bandwith migration may pass without dirty limit,
+     * so we need to decrease a bandwidth.
+     */
+    const int64_t dirtylimit_period = 1000, dirtylimit_value = 50;
+    const int64_t max_bandwidth = 400000000; /* ~400Mb/s */
+    const int64_t downtime_limit = 250; /* 250ms */
+    /*
+     * We migrate through unix-socket (> 500Mb/s).
+     * Thus, expected migration speed ~= bandwidth limit (< 500Mb/s).
+     * So, we can predict expected_threshold
+     */
+    const int64_t expected_threshold = max_bandwidth * downtime_limit / 1000;
+    int max_try_count = 10;
+    MigrateCommon args = {
+        .start = {
+            .hide_stderr = true,
+            .use_dirty_ring = true,
+        },
+        .listen_uri = uri,
+        .connect_uri = uri,
+    };
+
+    /* Start src, dst vm */
+    if (test_migrate_start(&from, &to, args.listen_uri, &args.start)) {
+        return;
+    }
+
+    /* Prepare for dirty limit migration and wait src vm show up */
+    migrate_dirty_limit_wait_showup(from, dirtylimit_period, dirtylimit_value);
+
+    /* Start migrate */
+    migrate_qmp(from, uri, "{}");
+
+    /* Wait for dirty limit throttle begin */
+    throttle_us_per_full = 0;
+    while (throttle_us_per_full == 0) {
+        throttle_us_per_full =
+        read_migrate_property_int(from, "dirty-limit-throttle-time-per-round");
+        usleep(100);
+        g_assert_false(got_src_stop);
+    }
+
+    /* Now cancel migrate and wait for dirty limit throttle switch off */
+    migrate_cancel(from);
+    wait_for_migration_status(from, "cancelled", NULL);
+
+    /* Check if dirty limit throttle switched off, set timeout 1ms */
+    do {
+        throttle_us_per_full =
+        read_migrate_property_int(from, "dirty-limit-throttle-time-per-round");
+        usleep(100);
+        g_assert_false(got_src_stop);
+    } while (throttle_us_per_full != 0 && --max_try_count);
+
+    /* Assert dirty limit is not in service */
+    g_assert_cmpint(throttle_us_per_full, ==, 0);
+
+    args = (MigrateCommon) {
+        .start = {
+            .only_target = true,
+            .use_dirty_ring = true,
+        },
+        .listen_uri = uri,
+        .connect_uri = uri,
+    };
+
+    /* Restart dst vm, src vm already show up so we needn't wait anymore */
+    if (test_migrate_start(&from, &to, args.listen_uri, &args.start)) {
+        return;
+    }
+
+    /* Start migrate */
+    migrate_qmp(from, uri, "{}");
+
+    /* Wait for dirty limit throttle begin */
+    throttle_us_per_full = 0;
+    while (throttle_us_per_full == 0) {
+        throttle_us_per_full =
+        read_migrate_property_int(from, "dirty-limit-throttle-time-per-round");
+        usleep(100);
+        g_assert_false(got_src_stop);
+    }
+
+    /*
+     * The dirty limit rate should equals the return value of
+     * query-vcpu-dirty-limit if dirty limit cap set
+     */
+    g_assert_cmpint(dirtylimit_value, ==, get_limit_rate(from));
+
+    /* Now, we have tested if dirty limit works, let it converge */
+    migrate_set_parameter_int(from, "downtime-limit", downtime_limit);
+    migrate_set_parameter_int(from, "max-bandwidth", max_bandwidth);
+
+    /*
+     * Wait for pre-switchover status to check if migration
+     * satisfy the convergence condition
+     */
+    wait_for_migration_status(from, "pre-switchover", NULL);
+
+    remaining = read_ram_property_int(from, "remaining");
+    g_assert_cmpint(remaining, <,
+                    (expected_threshold + expected_threshold / 100));
+
+    migrate_continue(from, "pre-switchover");
+
+    qtest_qmp_eventwait(to, "RESUME");
+
+    wait_for_serial("dest_serial");
+    wait_for_migration_complete(from);
+
+    test_migrate_end(from, to, true);
+}
+
 static bool kvm_dirty_ring_supported(void)
 {
 #if defined(__linux__) && defined(HOST_X86_64)
@@ -3165,6 +3325,10 @@ int main(int argc, char **argv)
      */
     if (g_test_slow()) {
         qtest_add_func("/migration/auto_converge", test_migrate_auto_converge);
+        if (g_str_equal(arch, "x86_64") &&
+            has_kvm && kvm_dirty_ring_supported()) {
+            qtest_add_func("/migration/dirty_limit", test_migrate_dirty_limit);
+        }
     }
     qtest_add_func("/migration/multifd/tcp/plain/none",
                    test_multifd_tcp_none);
-- 
2.39.1

Re: [v3 3/6] tests: Add migration dirty-limit capability test

[Juan Quintela]

Hyman Huang <yong.huang@smartx.com> wrote:
> Add migration dirty-limit capability test if kernel support
> dirty ring.
>
> Migration dirty-limit capability introduce dirty limit
> capability, two parameters: x-vcpu-dirty-limit-period and
> vcpu-dirty-limit are introduced to implement the live
> migration with dirty limit.
>
> The test case does the following things:
> 1. start src, dst vm and enable dirty-limit capability
> 2. start migrate and set cancel it to check if dirty limit
>    stop working.
> 3. restart dst vm
> 4. start migrate and enable dirty-limit capability
> 5. check if migration satisfy the convergence condition
>    during pre-switchover phase.
>
> Note that this test case involves many passes, so it runs
> in slow mode only.
>
> Signed-off-by: Hyman Huang <yong.huang@smartx.com>
> Acked-by: Peter Xu <peterx@redhat.com>
> Reviewed-by: Fabiano Rosas <farosas@suse.de>
> Message-Id: <a05e931ed147696bd5924e0582db67a734547a3f.1697815117.git.yong.huang@smartx.com>

Reviewed-by: Juan Quintela <quintela@redhat.com>

[v3 4/6] tests/migration: Introduce dirty-ring-size option into guestperf

[Hyman Huang]

Dirty ring size configuration is not supported by guestperf tool.

Introduce dirty-ring-size (ranges in [1024, 65536]) option so
developers can play with dirty-ring and dirty-limit feature easier.

To set dirty ring size with 4096 during migration test:
$ ./tests/migration/guestperf.py --dirty-ring-size 4096 xxx

Signed-off-by: Hyman Huang <yong.huang@smartx.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Message-Id: <bd9f195883fb5081f67f680bd2972a4b0a5b3520.1697815117.git.yong.huang@smartx.com>
---
 tests/migration/guestperf/engine.py   | 6 +++++-
 tests/migration/guestperf/hardware.py | 8 ++++++--
 tests/migration/guestperf/shell.py    | 6 +++++-
 3 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/tests/migration/guestperf/engine.py b/tests/migration/guestperf/engine.py
index da96ca034a..aabf6de4d9 100644
--- a/tests/migration/guestperf/engine.py
+++ b/tests/migration/guestperf/engine.py
@@ -325,7 +325,6 @@ def _get_common_args(self, hardware, tunnelled=False):
             cmdline = "'" + cmdline + "'"
 
         argv = [
-            "-accel", "kvm",
             "-cpu", "host",
             "-kernel", self._kernel,
             "-initrd", self._initrd,
@@ -333,6 +332,11 @@ def _get_common_args(self, hardware, tunnelled=False):
             "-m", str((hardware._mem * 1024) + 512),
             "-smp", str(hardware._cpus),
         ]
+        if hardware._dirty_ring_size:
+            argv.extend(["-accel", "kvm,dirty-ring-size=%s" %
+                         hardware._dirty_ring_size])
+        else:
+            argv.extend(["-accel", "kvm"])
 
         argv.extend(self._get_qemu_serial_args())
 
diff --git a/tests/migration/guestperf/hardware.py b/tests/migration/guestperf/hardware.py
index 3145785ffd..f779cc050b 100644
--- a/tests/migration/guestperf/hardware.py
+++ b/tests/migration/guestperf/hardware.py
@@ -23,7 +23,8 @@ def __init__(self, cpus=1, mem=1,
                  src_cpu_bind=None, src_mem_bind=None,
                  dst_cpu_bind=None, dst_mem_bind=None,
                  prealloc_pages = False,
-                 huge_pages=False, locked_pages=False):
+                 huge_pages=False, locked_pages=False,
+                 dirty_ring_size=0):
         self._cpus = cpus
         self._mem = mem # GiB
         self._src_mem_bind = src_mem_bind # List of NUMA nodes
@@ -33,6 +34,7 @@ def __init__(self, cpus=1, mem=1,
         self._prealloc_pages = prealloc_pages
         self._huge_pages = huge_pages
         self._locked_pages = locked_pages
+        self._dirty_ring_size = dirty_ring_size
 
 
     def serialize(self):
@@ -46,6 +48,7 @@ def serialize(self):
             "prealloc_pages": self._prealloc_pages,
             "huge_pages": self._huge_pages,
             "locked_pages": self._locked_pages,
+            "dirty_ring_size": self._dirty_ring_size,
         }
 
     @classmethod
@@ -59,4 +62,5 @@ def deserialize(cls, data):
             data["dst_mem_bind"],
             data["prealloc_pages"],
             data["huge_pages"],
-            data["locked_pages"])
+            data["locked_pages"],
+            data["dirty_ring_size"])
diff --git a/tests/migration/guestperf/shell.py b/tests/migration/guestperf/shell.py
index 8a809e3dda..7d6b8cd7cf 100644
--- a/tests/migration/guestperf/shell.py
+++ b/tests/migration/guestperf/shell.py
@@ -60,6 +60,8 @@ def __init__(self):
         parser.add_argument("--prealloc-pages", dest="prealloc_pages", default=False)
         parser.add_argument("--huge-pages", dest="huge_pages", default=False)
         parser.add_argument("--locked-pages", dest="locked_pages", default=False)
+        parser.add_argument("--dirty-ring-size", dest="dirty_ring_size",
+                            default=0, type=int)
 
         self._parser = parser
 
@@ -89,7 +91,9 @@ def split_map(value):
 
                         locked_pages=args.locked_pages,
                         huge_pages=args.huge_pages,
-                        prealloc_pages=args.prealloc_pages)
+                        prealloc_pages=args.prealloc_pages,
+
+                        dirty_ring_size=args.dirty_ring_size)
 
 
 class Shell(BaseShell):
-- 
2.39.1

[v3 5/6] tests/migration: Introduce dirty-limit into guestperf

[Hyman Huang]

Currently, guestperf does not cover the dirty-limit
migration, support this feature.

Note that dirty-limit requires 'dirty-ring-size' set.

To enable dirty-limit, setting x-vcpu-dirty-limit-period
as 500ms and x-vcpu-dirty-limit as 10MB/s:
$ ./tests/migration/guestperf.py \
    --dirty-ring-size 4096 \
    --dirty-limit --x-vcpu-dirty-limit-period 500 \
    --vcpu-dirty-limit 10 --output output.json \

To run the entire standardized set of dirty-limit-enabled
comparisons, with unix migration:
$ ./tests/migration/guestperf-batch.py \
    --dirty-ring-size 4096 \
    --dst-host localhost --transport unix \
    --filter compr-dirty-limit* --output outputdir

Signed-off-by: Hyman Huang <yong.huang@smartx.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Message-Id: <516e7a55dfc6e33d33510be37eb24223de5dc072.1697815117.git.yong.huang@smartx.com>
---
 tests/migration/guestperf/comparison.py | 23 +++++++++++++++++++++++
 tests/migration/guestperf/engine.py     | 17 +++++++++++++++++
 tests/migration/guestperf/progress.py   | 16 ++++++++++++++--
 tests/migration/guestperf/scenario.py   | 11 ++++++++++-
 tests/migration/guestperf/shell.py      | 18 +++++++++++++++++-
 5 files changed, 81 insertions(+), 4 deletions(-)

diff --git a/tests/migration/guestperf/comparison.py b/tests/migration/guestperf/comparison.py
index c03b3f6d7e..42cc0372d1 100644
--- a/tests/migration/guestperf/comparison.py
+++ b/tests/migration/guestperf/comparison.py
@@ -135,4 +135,27 @@ def __init__(self, name, scenarios):
         Scenario("compr-multifd-channels-64",
                  multifd=True, multifd_channels=64),
     ]),
+
+    # Looking at effect of dirty-limit with
+    # varying x_vcpu_dirty_limit_period
+    Comparison("compr-dirty-limit-period", scenarios = [
+        Scenario("compr-dirty-limit-period-500",
+                 dirty_limit=True, x_vcpu_dirty_limit_period=500),
+        Scenario("compr-dirty-limit-period-800",
+                 dirty_limit=True, x_vcpu_dirty_limit_period=800),
+        Scenario("compr-dirty-limit-period-1000",
+                 dirty_limit=True, x_vcpu_dirty_limit_period=1000),
+    ]),
+
+
+    # Looking at effect of dirty-limit with
+    # varying vcpu_dirty_limit
+    Comparison("compr-dirty-limit", scenarios = [
+        Scenario("compr-dirty-limit-10MB",
+                 dirty_limit=True, vcpu_dirty_limit=10),
+        Scenario("compr-dirty-limit-20MB",
+                 dirty_limit=True, vcpu_dirty_limit=20),
+        Scenario("compr-dirty-limit-50MB",
+                 dirty_limit=True, vcpu_dirty_limit=50),
+    ]),
 ]
diff --git a/tests/migration/guestperf/engine.py b/tests/migration/guestperf/engine.py
index aabf6de4d9..608d7270f6 100644
--- a/tests/migration/guestperf/engine.py
+++ b/tests/migration/guestperf/engine.py
@@ -102,6 +102,8 @@ def _migrate_progress(self, vm):
             info.get("expected-downtime", 0),
             info.get("setup-time", 0),
             info.get("cpu-throttle-percentage", 0),
+            info.get("dirty-limit-throttle-time-per-round", 0),
+            info.get("dirty-limit-ring-full-time", 0),
         )
 
     def _migrate(self, hardware, scenario, src, dst, connect_uri):
@@ -203,6 +205,21 @@ def _migrate(self, hardware, scenario, src, dst, connect_uri):
             resp = dst.cmd("migrate-set-parameters",
                            multifd_channels=scenario._multifd_channels)
 
+        if scenario._dirty_limit:
+            if not hardware._dirty_ring_size:
+                raise Exception("dirty ring size must be configured when "
+                                "testing dirty limit migration")
+
+            resp = src.cmd("migrate-set-capabilities",
+                           capabilities = [
+                               { "capability": "dirty-limit",
+                                 "state": True }
+                           ])
+            resp = src.cmd("migrate-set-parameters",
+                x_vcpu_dirty_limit_period=scenario._x_vcpu_dirty_limit_period)
+            resp = src.cmd("migrate-set-parameters",
+                           vcpu_dirty_limit=scenario._vcpu_dirty_limit)
+
         resp = src.cmd("migrate", uri=connect_uri)
 
         post_copy = False
diff --git a/tests/migration/guestperf/progress.py b/tests/migration/guestperf/progress.py
index ab1ee57273..d490584217 100644
--- a/tests/migration/guestperf/progress.py
+++ b/tests/migration/guestperf/progress.py
@@ -81,7 +81,9 @@ def __init__(self,
                  downtime,
                  downtime_expected,
                  setup_time,
-                 throttle_pcent):
+                 throttle_pcent,
+                 dirty_limit_throttle_time_per_round,
+                 dirty_limit_ring_full_time):
 
         self._status = status
         self._ram = ram
@@ -91,6 +93,10 @@ def __init__(self,
         self._downtime_expected = downtime_expected
         self._setup_time = setup_time
         self._throttle_pcent = throttle_pcent
+        self._dirty_limit_throttle_time_per_round = \
+            dirty_limit_throttle_time_per_round
+        self._dirty_limit_ring_full_time = \
+            dirty_limit_ring_full_time
 
     def serialize(self):
         return {
@@ -102,6 +108,10 @@ def serialize(self):
             "downtime_expected": self._downtime_expected,
             "setup_time": self._setup_time,
             "throttle_pcent": self._throttle_pcent,
+            "dirty_limit_throttle_time_per_round":
+                self._dirty_limit_throttle_time_per_round,
+            "dirty_limit_ring_full_time":
+                self._dirty_limit_ring_full_time,
         }
 
     @classmethod
@@ -114,4 +124,6 @@ def deserialize(cls, data):
             data["downtime"],
             data["downtime_expected"],
             data["setup_time"],
-            data["throttle_pcent"])
+            data["throttle_pcent"],
+            data["dirty_limit_throttle_time_per_round"],
+            data["dirty_limit_ring_full_time"])
diff --git a/tests/migration/guestperf/scenario.py b/tests/migration/guestperf/scenario.py
index de70d9b2f5..154c4f5d5f 100644
--- a/tests/migration/guestperf/scenario.py
+++ b/tests/migration/guestperf/scenario.py
@@ -30,7 +30,9 @@ def __init__(self, name,
                  auto_converge=False, auto_converge_step=10,
                  compression_mt=False, compression_mt_threads=1,
                  compression_xbzrle=False, compression_xbzrle_cache=10,
-                 multifd=False, multifd_channels=2):
+                 multifd=False, multifd_channels=2,
+                 dirty_limit=False, x_vcpu_dirty_limit_period=500,
+                 vcpu_dirty_limit=1):
 
         self._name = name
 
@@ -60,6 +62,10 @@ def __init__(self, name,
         self._multifd = multifd
         self._multifd_channels = multifd_channels
 
+        self._dirty_limit = dirty_limit
+        self._x_vcpu_dirty_limit_period = x_vcpu_dirty_limit_period
+        self._vcpu_dirty_limit = vcpu_dirty_limit
+
     def serialize(self):
         return {
             "name": self._name,
@@ -79,6 +85,9 @@ def serialize(self):
             "compression_xbzrle_cache": self._compression_xbzrle_cache,
             "multifd": self._multifd,
             "multifd_channels": self._multifd_channels,
+            "dirty_limit": self._dirty_limit,
+            "x_vcpu_dirty_limit_period": self._x_vcpu_dirty_limit_period,
+            "vcpu_dirty_limit": self._vcpu_dirty_limit,
         }
 
     @classmethod
diff --git a/tests/migration/guestperf/shell.py b/tests/migration/guestperf/shell.py
index 7d6b8cd7cf..c85d89efec 100644
--- a/tests/migration/guestperf/shell.py
+++ b/tests/migration/guestperf/shell.py
@@ -131,6 +131,17 @@ def __init__(self):
         parser.add_argument("--multifd-channels", dest="multifd_channels",
                             default=2, type=int)
 
+        parser.add_argument("--dirty-limit", dest="dirty_limit", default=False,
+                            action="store_true")
+
+        parser.add_argument("--x-vcpu-dirty-limit-period",
+                            dest="x_vcpu_dirty_limit_period",
+                            default=500, type=int)
+
+        parser.add_argument("--vcpu-dirty-limit",
+                            dest="vcpu_dirty_limit",
+                            default=1, type=int)
+
     def get_scenario(self, args):
         return Scenario(name="perfreport",
                         downtime=args.downtime,
@@ -154,7 +165,12 @@ def get_scenario(self, args):
                         compression_xbzrle_cache=args.compression_xbzrle_cache,
 
                         multifd=args.multifd,
-                        multifd_channels=args.multifd_channels)
+                        multifd_channels=args.multifd_channels,
+
+                        dirty_limit=args.dirty_limit,
+                        x_vcpu_dirty_limit_period=\
+                            args.x_vcpu_dirty_limit_period,
+                        vcpu_dirty_limit=args.vcpu_dirty_limit)
 
     def run(self, argv):
         args = self._parser.parse_args(argv)
-- 
2.39.1

[v3 6/6] docs/migration: Add the dirty limit section

[Hyman Huang]

The dirty limit feature has been introduced since the 8.1
QEMU release but has not reflected in the document, add a
section for that.

Signed-off-by: Hyman Huang <yong.huang@smartx.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Message-Id: <36194a8a23d937392bf13d9fff8e898030c827a3.1697815117.git.yong.huang@smartx.com>
---
 docs/devel/migration.rst | 71 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 71 insertions(+)

diff --git a/docs/devel/migration.rst b/docs/devel/migration.rst
index be913630c3..12c35f9bc4 100644
--- a/docs/devel/migration.rst
+++ b/docs/devel/migration.rst
@@ -590,6 +590,77 @@ path.
      Return path  - opened by main thread, written by main thread AND postcopy
      thread (protected by rp_mutex)
 
+Dirty limit
+=====================
+The dirty limit, short for dirty page rate upper limit, is a new capability
+introduced in the 8.1 QEMU release that uses a new algorithm based on the KVM
+dirty ring to throttle down the guest during live migration.
+
+The algorithm framework is as follows:
+
+::
+
+  ------------------------------------------------------------------------------
+  main   --------------> throttle thread ------------> PREPARE(1) <--------
+  thread  \                                                |              |
+           \                                               |              |
+            \                                              V              |
+             -\                                        CALCULATE(2)       |
+               \                                           |              |
+                \                                          |              |
+                 \                                         V              |
+                  \                                    SET PENALTY(3) -----
+                   -\                                      |
+                     \                                     |
+                      \                                    V
+                       -> virtual CPU thread -------> ACCEPT PENALTY(4)
+  ------------------------------------------------------------------------------
+
+When the qmp command qmp_set_vcpu_dirty_limit is called for the first time,
+the QEMU main thread starts the throttle thread. The throttle thread, once
+launched, executes the loop, which consists of three steps:
+
+  - PREPARE (1)
+
+     The entire work of PREPARE (1) is preparation for the second stage,
+     CALCULATE(2), as the name implies. It involves preparing the dirty
+     page rate value and the corresponding upper limit of the VM:
+     The dirty page rate is calculated via the KVM dirty ring mechanism,
+     which tells QEMU how many dirty pages a virtual CPU has had since the
+     last KVM_EXIT_DIRTY_RING_FULL exception; The dirty page rate upper
+     limit is specified by caller, therefore fetch it directly.
+
+  - CALCULATE (2)
+
+     Calculate a suitable sleep period for each virtual CPU, which will be
+     used to determine the penalty for the target virtual CPU. The
+     computation must be done carefully in order to reduce the dirty page
+     rate progressively down to the upper limit without oscillation. To
+     achieve this, two strategies are provided: the first is to add or
+     subtract sleep time based on the ratio of the current dirty page rate
+     to the limit, which is used when the current dirty page rate is far
+     from the limit; the second is to add or subtract a fixed time when
+     the current dirty page rate is close to the limit.
+
+  - SET PENALTY (3)
+
+     Set the sleep time for each virtual CPU that should be penalized based
+     on the results of the calculation supplied by step CALCULATE (2).
+
+After completing the three above stages, the throttle thread loops back
+to step PREPARE (1) until the dirty limit is reached.
+
+On the other hand, each virtual CPU thread reads the sleep duration and
+sleeps in the path of the KVM_EXIT_DIRTY_RING_FULL exception handler, that
+is ACCEPT PENALTY (4). Virtual CPUs tied with writing processes will
+obviously exit to the path and get penalized, whereas virtual CPUs involved
+with read processes will not.
+
+In summary, thanks to the KVM dirty ring technology, the dirty limit
+algorithm will restrict virtual CPUs as needed to keep their dirty page
+rate inside the limit. This leads to more steady reading performance during
+live migration and can aid in improving large guest responsiveness.
+
 Postcopy
 ========
 
-- 
2.39.1

Re: [v3 6/6] docs/migration: Add the dirty limit section

[Juan Quintela]

Hyman Huang <yong.huang@smartx.com> wrote:
> The dirty limit feature has been introduced since the 8.1
> QEMU release but has not reflected in the document, add a
> section for that.
>
> Signed-off-by: Hyman Huang <yong.huang@smartx.com>
> Reviewed-by: Fabiano Rosas <farosas@suse.de>
> Message-Id: <36194a8a23d937392bf13d9fff8e898030c827a3.1697815117.git.yong.huang@smartx.com>

Reviewed-by: Juan Quintela <quintela@redhat.com>

I queued the whole series.  I didn't comment about the guestperf script
changes because I am not familiar with that part.


> ---
>  docs/devel/migration.rst | 71 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 71 insertions(+)
>
> diff --git a/docs/devel/migration.rst b/docs/devel/migration.rst
> index be913630c3..12c35f9bc4 100644
> --- a/docs/devel/migration.rst
> +++ b/docs/devel/migration.rst
> @@ -590,6 +590,77 @@ path.
>       Return path  - opened by main thread, written by main thread AND postcopy
>       thread (protected by rp_mutex)
>  
> +Dirty limit
> +=====================

Too long, I fixed it by hand.