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[PATCH v2 3/3] multifd: Send using asynchronous write on nocomp to send


From: Leonardo Bras
Subject: [PATCH v2 3/3] multifd: Send using asynchronous write on nocomp to send RAM pages.
Date: Wed, 22 Sep 2021 02:03:40 -0300

Change multifd nocomp version to use asynchronous write for RAM pages, and
benefit of MSG_ZEROCOPY when it's available.

The asynchronous flush happens on cleanup only, before destroying the 
QIOChannel.

This will work fine on RAM migration because the RAM pages are not usually 
freed,
and there is no problem on changing the pages content between async_send() and
the actual sending of the buffer, because this change will dirty the page and
cause it to be re-sent on a next iteration anyway.

Signed-off-by: Leonardo Bras <leobras@redhat.com>
---
 migration/multifd.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/migration/multifd.c b/migration/multifd.c
index 377da78f5b..d247207a0a 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -105,7 +105,7 @@ static int nocomp_send_prepare(MultiFDSendParams *p, 
uint32_t used,
  */
 static int nocomp_send_write(MultiFDSendParams *p, uint32_t used, Error **errp)
 {
-    return qio_channel_writev_all(p->c, p->pages->iov, used, errp);
+    return qio_channel_async_writev_all(p->c, p->pages->iov, used, errp);
 }
 
 /**
@@ -546,6 +546,7 @@ void multifd_save_cleanup(void)
         MultiFDSendParams *p = &multifd_send_state->params[i];
         Error *local_err = NULL;
 
+        qio_channel_async_flush(p->c, NULL);
         socket_send_channel_destroy(p->c);
         p->c = NULL;
         qemu_mutex_destroy(&p->mutex);
-- 
2.33.0




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