Migration patches for 2026-02-17

[PULL 19/32] migration/postcopy: Send device states without copying buffer

Fabiano Rosas posted 32 patches 1 month, 3 weeks ago

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Maintainers: Peter Maydell <peter.maydell@linaro.org>, "Michael S. Tsirkin" <mst@redhat.com>, Jason Wang <jasowang@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Fam Zheng <fam@euphon.net>, Peter Xu <peterx@redhat.com>, Fabiano Rosas <farosas@suse.de>, Mark Kanda <mark.kanda@oracle.com>, Ben Chaney <bchaney@akamai.com>, Alex Williamson <alex@shazbot.org>, "Cédric Le Goater" <clg@redhat.com>, Hailiang Zhang <zhanghailiang@xfusion.com>, Markus Armbruster <armbru@redhat.com>, Stefano Garzarella <sgarzare@redhat.com>, Laurent Vivier <lvivier@redhat.com>, "Marc-André Lureau" <marcandre.lureau@redhat.com>

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[PULL 19/32] migration/postcopy: Send device states without copying buffer

Posted by Fabiano Rosas 1 month, 3 weeks ago

From: Peter Xu <peterx@redhat.com>

Put buffer can be async as long as the flush happens before the buffer will
be recycled / reused.  Do it for postcopy package data.  Quick measurement
shows a small VM the time to push / flush the package shrinks from 91us to
38us.

Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Tested-by: Lukas Straub <lukasstraub2@web.de>
Link: https://lore.kernel.org/qemu-devel/20260127185254.3954634-14-peterx@redhat.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
---
 migration/savevm.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/migration/savevm.c b/migration/savevm.c
index 9d2109718a..d41e89228d 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1136,7 +1136,8 @@ int qemu_savevm_send_packaged(QEMUFile *f, const uint8_t *buf, size_t len)
     trace_qemu_savevm_send_packaged();
     qemu_savevm_command_send(f, MIG_CMD_PACKAGED, 4, (uint8_t *)&tmp);
 
-    qemu_put_buffer(f, buf, len);
+    /* We can use async put because the qemufile will be flushed right away */
+    qemu_put_buffer_async(f, buf, len, false);
     qemu_fflush(f);
 
     return 0;
-- 
2.51.0