From 662b91cbf6bebfa4f38fe2d1b1868d316bfe8838 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= Date: Tue, 10 Jun 2025 13:36:45 +0100 Subject: [PATCH 15/43] hw/audio/ac97: skip automatic zero-init of large arrays 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: [7/31] 5c4f1eea2eab9ef363ac7f0076725fc5767ee51f (stefanha/centos-stream-qemu-kvm) The 'read_audio' & 'write_audio' methods have a 4k byte array used for copying data between the audio backend and device. Skip the automatic zero-init of these arrays to eliminate the performance overhead in the I/O hot path. The 'tmpbuf' array will be fully initialized when reading data from the audio backend and/or device memory. Signed-off-by: Daniel P. Berrangé Reviewed-by: Stefan Hajnoczi Message-id: 20250610123709.835102-8-berrange@redhat.com Signed-off-by: Stefan Hajnoczi (cherry picked from commit 2553d2d26a9d0f46386bf8c37d184567e5cede6c) Signed-off-by: Stefan Hajnoczi --- hw/audio/ac97.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/hw/audio/ac97.c b/hw/audio/ac97.c index 05c573776e..2b290cb2b1 100644 --- a/hw/audio/ac97.c +++ b/hw/audio/ac97.c @@ -886,7 +886,7 @@ static void nabm_writel(void *opaque, uint32_t addr, uint32_t val) static int write_audio(AC97LinkState *s, AC97BusMasterRegs *r, int max, int *stop) { - uint8_t tmpbuf[4096]; + QEMU_UNINITIALIZED uint8_t tmpbuf[4096]; uint32_t addr = r->bd.addr; uint32_t temp = r->picb << 1; uint32_t written = 0; @@ -959,7 +959,7 @@ static void write_bup(AC97LinkState *s, int elapsed) static int read_audio(AC97LinkState *s, AC97BusMasterRegs *r, int max, int *stop) { - uint8_t tmpbuf[4096]; + QEMU_UNINITIALIZED uint8_t tmpbuf[4096]; uint32_t addr = r->bd.addr; uint32_t temp = r->picb << 1; uint32_t nread = 0; -- 2.39.3