From dfe44e34228c242f539f61383c431b6b9acd86f0 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= Date: Tue, 10 Jun 2025 13:36:43 +0100 Subject: [PATCH 13/43] chardev/char-pty: 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: 381: Solve -ftrivial-auto-var-init performance regression with QEMU_UNINITIALIZED RH-Jira: RHEL-95479 RH-Acked-by: Miroslav Rezanina RH-Commit: [5/31] e41c3503091674e90cc7c17f202e5d4ae1f417cd (stefanha/centos-stream-qemu-kvm) The 'pty_chr_read' method has a 4k byte array used for copying data between the PTY and device. Skip the automatic zero-init of this array to eliminate the performance overhead in the I/O hot path. The 'buf' array will be fully initialized when reading data off the PTY. Signed-off-by: Daniel P. Berrangé Reviewed-by: Stefan Hajnoczi Message-id: 20250610123709.835102-6-berrange@redhat.com Signed-off-by: Stefan Hajnoczi (cherry picked from commit 45bb7fb21c8d18294a9f92da99d01ab3c67c7df2) Signed-off-by: Stefan Hajnoczi --- chardev/char-pty.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/chardev/char-pty.c b/chardev/char-pty.c index 6a2c1dc13a..f484aac78d 100644 --- a/chardev/char-pty.c +++ b/chardev/char-pty.c @@ -154,7 +154,7 @@ static gboolean pty_chr_read(QIOChannel *chan, GIOCondition cond, void *opaque) Chardev *chr = CHARDEV(opaque); PtyChardev *s = PTY_CHARDEV(opaque); gsize len; - uint8_t buf[CHR_READ_BUF_LEN]; + QEMU_UNINITIALIZED uint8_t buf[CHR_READ_BUF_LEN]; ssize_t ret; len = sizeof(buf); -- 2.39.3