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Migration Pull request (20231103)

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Hi
 
 In this PULL:
 - dirty limit fixes (hyman)
 - coverity issues (juan)
 
 Please apply.
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Merge tag 'migration-20231103-pull-request' of https://gitlab.com/juan.quintela/qemu into staging

Migration Pull request (20231103)

Hi

In this PULL:
- dirty limit fixes (hyman)
- coverity issues (juan)

Please apply.

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# gpg: Signature made Fri 03 Nov 2023 20:04:40 HKT
# gpg:                using RSA key 1899FF8EDEBF58CCEE034B82F487EF185872D723
# gpg: Good signature from "Juan Quintela <quintela@redhat.com>" [full]
# gpg:                 aka "Juan Quintela <quintela@trasno.org>" [full]
# Primary key fingerprint: 1899 FF8E DEBF 58CC EE03  4B82 F487 EF18 5872 D723

* tag 'migration-20231103-pull-request' of https://gitlab.com/juan.quintela/qemu:
  migration: Unlock mutex in error case
  docs/migration: Add the dirty limit section
  tests/migration: Introduce dirty-limit into guestperf
  tests/migration: Introduce dirty-ring-size option into guestperf
  tests: Add migration dirty-limit capability test
  system/dirtylimit: Drop the reduplicative check
  system/dirtylimit: Fix a race situation

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2023-11-06 08:37:22 +08:00
commit f3604191e2
10 changed files with 401 additions and 73 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

71
docs/devel/migration.rst
View File

@ -594,6 +594,77 @@ 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
========

110
migration/ram.c
View File

@ -3030,71 +3030,71 @@ static int ram_save_iterate(QEMUFile *f, void *opaque)
* MAX_WAIT (if curious, further see commit 4508bd9ed8053ce) below, which
* guarantees that we'll at least released it in a regular basis.
*/
qemu_mutex_lock(&rs->bitmap_mutex);
WITH_RCU_READ_LOCK_GUARD() {
if (ram_list.version != rs->last_version) {
ram_state_reset(rs);
}
/* Read version before ram_list.blocks */
smp_rmb();
ret = rdma_registration_start(f, RAM_CONTROL_ROUND);
if (ret < 0) {
qemu_file_set_error(f, ret);
goto out;
}
t0 = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
i = 0;
while ((ret = migration_rate_exceeded(f)) == 0 ||
postcopy_has_request(rs)) {
int pages;
if (qemu_file_get_error(f)) {
break;
WITH_QEMU_LOCK_GUARD(&rs->bitmap_mutex) {
WITH_RCU_READ_LOCK_GUARD() {
if (ram_list.version != rs->last_version) {
ram_state_reset(rs);
}
pages = ram_find_and_save_block(rs);
/* no more pages to sent */
if (pages == 0) {
done = 1;
break;
/* Read version before ram_list.blocks */
smp_rmb();
ret = rdma_registration_start(f, RAM_CONTROL_ROUND);
if (ret < 0) {
qemu_file_set_error(f, ret);
goto out;
}
if (pages < 0) {
qemu_file_set_error(f, pages);
break;
}
t0 = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
i = 0;
while ((ret = migration_rate_exceeded(f)) == 0 ||
postcopy_has_request(rs)) {
int pages;
rs->target_page_count += pages;
/*
* During postcopy, it is necessary to make sure one whole host
* page is sent in one chunk.
*/
if (migrate_postcopy_ram()) {
compress_flush_data();
}
/*
* we want to check in the 1st loop, just in case it was the 1st
* time and we had to sync the dirty bitmap.
* qemu_clock_get_ns() is a bit expensive, so we only check each
* some iterations
*/
if ((i & 63) == 0) {
uint64_t t1 = (qemu_clock_get_ns(QEMU_CLOCK_REALTIME) - t0) /
1000000;
if (t1 > MAX_WAIT) {
trace_ram_save_iterate_big_wait(t1, i);
if (qemu_file_get_error(f)) {
break;
}
pages = ram_find_and_save_block(rs);
/* no more pages to sent */
if (pages == 0) {
done = 1;
break;
}
if (pages < 0) {
qemu_file_set_error(f, pages);
break;
}
rs->target_page_count += pages;
/*
* During postcopy, it is necessary to make sure one whole host
* page is sent in one chunk.
*/
if (migrate_postcopy_ram()) {
compress_flush_data();
}
/*
* we want to check in the 1st loop, just in case it was the 1st
* time and we had to sync the dirty bitmap.
* qemu_clock_get_ns() is a bit expensive, so we only check each
* some iterations
*/
if ((i & 63) == 0) {
uint64_t t1 = (qemu_clock_get_ns(QEMU_CLOCK_REALTIME) - t0) /
1000000;
if (t1 > MAX_WAIT) {
trace_ram_save_iterate_big_wait(t1, i);
break;
}
}
i++;
}
i++;
}
}
qemu_mutex_unlock(&rs->bitmap_mutex);
/*
* Must occur before EOS (or any QEMUFile operation)

24
system/dirtylimit.c
View File

@ -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();
}
}
@ -644,10 +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();
}

23
tests/migration/guestperf/comparison.py
View File

@ -135,4 +135,27 @@ COMPARISONS = [
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),
]),
]

23
tests/migration/guestperf/engine.py
View File

@ -102,6 +102,8 @@ class Engine(object):
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 @@ class Engine(object):
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
@ -325,7 +342,6 @@ class Engine(object):
cmdline = "'" + cmdline + "'"
argv = [
"-accel", "kvm",
"-cpu", "host",
"-kernel", self._kernel,
"-initrd", self._initrd,
@ -333,6 +349,11 @@ class Engine(object):
"-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())

8
tests/migration/guestperf/hardware.py
View File

@ -23,7 +23,8 @@ class Hardware(object):
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 @@ class Hardware(object):
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 @@ class Hardware(object):
"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 @@ class Hardware(object):
data["dst_mem_bind"],
data["prealloc_pages"],
data["huge_pages"],
data["locked_pages"])
data["locked_pages"],
data["dirty_ring_size"])

16
tests/migration/guestperf/progress.py
View File

@ -81,7 +81,9 @@ class Progress(object):
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 @@ class Progress(object):
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 @@ class Progress(object):
"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 @@ class Progress(object):
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"])

11
tests/migration/guestperf/scenario.py
View File

@ -30,7 +30,9 @@ class Scenario(object):
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 @@ class Scenario(object):
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 @@ class Scenario(object):
"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

24
tests/migration/guestperf/shell.py
View File

@ -60,6 +60,8 @@ class BaseShell(object):
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 @@ class BaseShell(object):
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):
@ -127,6 +131,17 @@ class Shell(BaseShell):
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,
@ -150,7 +165,12 @@ class Shell(BaseShell):
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)

164
tests/qtest/migration-test.c
View File

@ -3091,6 +3091,166 @@ 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)
@ -3301,6 +3461,10 @@ 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);