From c7114f381bfa2663bdaa368b7b0dca764e28a07e Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= Date: Tue, 10 Jun 2025 13:36:42 +0100 Subject: [PATCH 12/43] chardev/char-fd: 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: [4/31] b26dc4c1b9677adb1332c778e6c9ec452952f4c1 (stefanha/centos-stream-qemu-kvm) The 'fd_chr_read' method has a 4k byte array used for copying data between the socket 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 network socket. Signed-off-by: Daniel P. Berrangé Reviewed-by: Stefan Hajnoczi Message-id: 20250610123709.835102-5-berrange@redhat.com Signed-off-by: Stefan Hajnoczi (cherry picked from commit a503bdc22b91869e3bf45522e36b122889465306) Signed-off-by: Stefan Hajnoczi --- chardev/char-fd.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/chardev/char-fd.c b/chardev/char-fd.c index d2c4923359..8dd662c066 100644 --- a/chardev/char-fd.c +++ b/chardev/char-fd.c @@ -50,7 +50,7 @@ static gboolean fd_chr_read(QIOChannel *chan, GIOCondition cond, void *opaque) Chardev *chr = CHARDEV(opaque); FDChardev *s = FD_CHARDEV(opaque); int 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