[Qemu-devel] [PATCH] migration/postcopy: Update the bandwidth during postcopy

[Qemu-devel] [PATCH] migration/postcopy: Update the bandwidth during postcopy

[Dr. David Alan Gilbert (git)]

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

The recently added max-postcopy-bandwidth parameter is only read
at the transition from precopy->postcopy where as the older
max-bandwidth parameter updates the migration bandwidth when changed
even if the migration is already running.

Fix this discrepency so that:
  a) You can change the bandwidth during postcopy by setting
     max-postcopy-bandwidth

  b) Changing max-bandwidth during postcopy has no effect
     (it currently changes the postcopy bandwidth which isn't
     expected).

Fixes: 7e555c6c
bz: https://bugzilla.redhat.com/show_bug.cgi?id=1686321
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 migration/migration.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/migration/migration.c b/migration/migration.c
index df6fd8e0e5..221f1b9ced 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -1347,7 +1347,7 @@ static void migrate_params_apply(MigrateSetParameters *params, Error **errp)
 
     if (params->has_max_bandwidth) {
         s->parameters.max_bandwidth = params->max_bandwidth;
-        if (s->to_dst_file) {
+        if (s->to_dst_file && !migration_in_postcopy()) {
             qemu_file_set_rate_limit(s->to_dst_file,
                                 s->parameters.max_bandwidth / XFER_LIMIT_RATIO);
         }
@@ -1379,6 +1379,10 @@ static void migrate_params_apply(MigrateSetParameters *params, Error **errp)
     }
     if (params->has_max_postcopy_bandwidth) {
         s->parameters.max_postcopy_bandwidth = params->max_postcopy_bandwidth;
+        if (s->to_dst_file && migration_in_postcopy()) {
+            qemu_file_set_rate_limit(s->to_dst_file,
+                    s->parameters.max_postcopy_bandwidth / XFER_LIMIT_RATIO);
+        }
     }
     if (params->has_max_cpu_throttle) {
         s->parameters.max_cpu_throttle = params->max_cpu_throttle;
-- 
2.20.1

Re: [Qemu-devel] [PATCH] migration/postcopy: Update the bandwidth during postcopy

[Peter Xu]

On Fri, Mar 08, 2019 at 10:12:10AM +0000, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> 
> The recently added max-postcopy-bandwidth parameter is only read
> at the transition from precopy->postcopy where as the older
> max-bandwidth parameter updates the migration bandwidth when changed
> even if the migration is already running.
> 
> Fix this discrepency so that:
>   a) You can change the bandwidth during postcopy by setting
>      max-postcopy-bandwidth
> 
>   b) Changing max-bandwidth during postcopy has no effect
>      (it currently changes the postcopy bandwidth which isn't
>      expected).
> 
> Fixes: 7e555c6c
> bz: https://bugzilla.redhat.com/show_bug.cgi?id=1686321
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

Reviewed-by: Peter Xu <peterx@redhat.com>

Now in qapi/migration.json it's not mentioning precopy in the
max-bandwidth entry which seems to work even for postcopy but it'll
not:

# @max-bandwidth: to set maximum speed for migration. maximum speed in
#                 bytes per second. (Since 2.8)

Should we consider to touch that up too to match everything?

-- 
Peter Xu