We've recently added support for direct-io with multifd, which brings
performance benefits, but creates a non-uniform user interface by
coupling direct-io with the multifd capability. This means that users
cannot keep the direct-io flag enabled while disabling multifd.
Libvirt in particular already has support for direct-io and parallel
migration separately from each other, so it would be a regression to
now require both options together. It's relatively simple for QEMU to
add support for direct-io migration without multifd, so let's do this
in order to keep both options decoupled.
We cannot simply enable the O_DIRECT flag, however, because not all IO
performed by the migration thread satisfies the alignment requirements
of O_DIRECT. There are many small read & writes that add headers and
synchronization flags to the stream, which at the moment are required
to always be present.
Fortunately, due to fixed-ram migration there is a discernible moment
where only RAM pages are written to the migration file. Enable
direct-io during that moment.
Signed-off-by: Fabiano Rosas <faro...@suse.de>
---
migration/ram.c | 40 ++++++++++++++++++++++++++++--------
tests/qtest/migration-test.c | 30 +++++++++++++++++++++++++++
2 files changed, 61 insertions(+), 9 deletions(-)
diff --git a/migration/ram.c b/migration/ram.c
index ceea586b06..5183d1f97c 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -3131,6 +3131,7 @@ static int ram_save_iterate(QEMUFile *f, void *opaque)
int i;
int64_t t0;
int done = 0;
+ Error **errp = NULL;
/*
* We'll take this lock a little bit long, but it's okay for two reasons.
@@ -3154,6 +3155,10 @@ static int ram_save_iterate(QEMUFile *f, void *opaque)
goto out;
}
+ if (!migration_direct_io_start(f, errp)) {
+ return -errno;
+ }
+
t0 = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
i = 0;
while ((ret = migration_rate_exceeded(f)) == 0 ||
@@ -3194,6 +3199,9 @@ static int ram_save_iterate(QEMUFile *f, void *opaque)
}
i++;
}
+ if (!migration_direct_io_finish(f, errp)) {
+ return -errno;
+ }
}
}
@@ -3242,7 +3250,8 @@ static int ram_save_complete(QEMUFile *f, void *opaque)
{
RAMState **temp = opaque;
RAMState *rs = *temp;
- int ret = 0;
+ int ret = 0, pages;
+ Error **errp = NULL;
rs->last_stage = !migration_in_colo_state();
@@ -3257,25 +3266,30 @@ static int ram_save_complete(QEMUFile *f, void *opaque)
return ret;
}
+ if (!migration_direct_io_start(f, errp)) {
+ return -errno;
+ }
+
/* try transferring iterative blocks of memory */
/* flush all remaining blocks regardless of rate limiting */
qemu_mutex_lock(&rs->bitmap_mutex);
while (true) {
- int pages;
-
pages = ram_find_and_save_block(rs);
- /* no more blocks to sent */
- if (pages == 0) {
+ if (pages <= 0) {
break;
}
- if (pages < 0) {
- qemu_mutex_unlock(&rs->bitmap_mutex);
- return pages;
- }
}
qemu_mutex_unlock(&rs->bitmap_mutex);
+ if (!migration_direct_io_finish(f, errp)) {
+ return -errno;
+ }
+
+ if (pages < 0) {
+ return pages;
+ }
+
ret = rdma_registration_stop(f, RAM_CONTROL_FINISH);
if (ret < 0) {
qemu_file_set_error(f, ret);
@@ -3920,6 +3934,10 @@ static bool read_ramblock_mapped_ram(QEMUFile *f,
RAMBlock *block,
void *host;
size_t read, unread, size;
+ if (!migration_direct_io_start(f, errp)) {
+ return false;
+ }
+
for (set_bit_idx = find_first_bit(bitmap, num_pages);
set_bit_idx < num_pages;
set_bit_idx = find_next_bit(bitmap, num_pages, clear_bit_idx + 1)) {
@@ -3955,6 +3973,10 @@ static bool read_ramblock_mapped_ram(QEMUFile *f,
RAMBlock *block,
}
}
+ if (!migration_direct_io_finish(f, errp)) {
+ return false;
+ }
+
return true;
err:
diff --git a/tests/qtest/migration-test.c b/tests/qtest/migration-test.c
index 5ced3b90c9..8c6a122c20 100644
--- a/tests/qtest/migration-test.c
+++ b/tests/qtest/migration-test.c
@@ -2245,6 +2245,34 @@ static void test_multifd_file_mapped_ram_dio(void)
test_file_common(&args, true);
}
+static void *mapped_ram_dio_start(QTestState *from, QTestState *to)
+{
+ migrate_mapped_ram_start(from, to);
+
+ migrate_set_parameter_bool(from, "direct-io", true);
+ migrate_set_parameter_bool(to, "direct-io", true);
+
+ return NULL;
+}
+
+static void test_precopy_file_mapped_ram_dio(void)
+{
+ g_autofree char *uri = g_strdup_printf("file:%s/%s", tmpfs,
+ FILE_TEST_FILENAME);
+ MigrateCommon args = {
+ .connect_uri = uri,
+ .listen_uri = "defer",
+ .start_hook = mapped_ram_dio_start,
+ };
+
+ if (!probe_o_direct_support(tmpfs)) {
+ g_test_skip("Filesystem does not support O_DIRECT");
+ return;
+ }
+
+ test_file_common(&args, true);
+}
+
#ifndef _WIN32
static void multifd_mapped_ram_fdset_end(QTestState *from, QTestState *to,
void *opaque)
@@ -3735,6 +3763,8 @@ int main(int argc, char **argv)
migration_test_add("/migration/multifd/file/mapped-ram/dio",
test_multifd_file_mapped_ram_dio);
+ migration_test_add("/migration/precopy/file/mapped-ram/dio",
+ test_precopy_file_mapped_ram_dio);
#ifndef _WIN32
qtest_add_func("/migration/multifd/file/mapped-ram/fdset",
--
2.35.3
