From 94310a4168257297e52058d5d6aea4a2d06630c6 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= Date: Tue, 10 Jun 2025 13:37:09 +0100 Subject: [PATCH 56/57] net/stream: skip automatic zero-init of large array MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit RH-Author: Stefan Hajnoczi RH-MergeRequest: 382: Solve -ftrivial-auto-var-init performance regression with QEMU_UNINITIALIZED RH-Jira: RHEL-99888 RH-Acked-by: Miroslav Rezanina RH-Commit: [30/30] 9dfec5c0e6358e3557bf58d66eee8e4ba6e93621 (stefanha/centos-stream-qemu-kvm) The 'net_stream_send' method has a 68k byte array used for copying data between guest and host. Skip the automatic zero-init of this array to eliminate the performance overhead in the I/O hot path. The 'buf1' array will be fully initialized when reading data off the network socket. Signed-off-by: Daniel P. Berrangé Reviewed-by: Stefan Hajnoczi Reviewed-by: Klaus Jensen Reviewed-by: Harsh Prateek Bora Message-id: 20250610123709.835102-32-berrange@redhat.com Signed-off-by: Stefan Hajnoczi (cherry picked from commit 837b87c4c5ba9ac7a255133c6642b8d578272a70) Signed-off-by: Stefan Hajnoczi --- net/stream.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/stream.c b/net/stream.c index 97e6ec6679..12384ffee5 100644 --- a/net/stream.c +++ b/net/stream.c @@ -148,7 +148,7 @@ static gboolean net_stream_send(QIOChannel *ioc, NetStreamState *s = data; int size; int ret; - char buf1[NET_BUFSIZE]; + QEMU_UNINITIALIZED char buf1[NET_BUFSIZE]; const char *buf; size = qio_channel_read(s->ioc, buf1, sizeof(buf1), NULL); -- 2.39.3