From 301bc6085046756e7ae0b5c2d4a95fa8cc88be0d Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= Date: Tue, 10 Jun 2025 13:36:46 +0100 Subject: [PATCH 16/43] hw/audio/cs4231a: 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: [8/31] 8633c398b929f3c4e0c1d7d5874b2fead4496a7d (stefanha/centos-stream-qemu-kvm) The 'cs_write_audio' method has a pair of byte arrays, one 4k in size and one 8k, which are used in converting audio samples. 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 a block of data from the guest. The 'linbuf' array will be fully initialized when converting the audio samples. Signed-off-by: Daniel P. Berrangé Reviewed-by: Stefan Hajnoczi Message-id: 20250610123709.835102-9-berrange@redhat.com Signed-off-by: Stefan Hajnoczi (cherry picked from commit ca2cc0385d97cea66cd54ee42553f385c403d4a6) Signed-off-by: Stefan Hajnoczi --- hw/audio/cs4231a.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/hw/audio/cs4231a.c b/hw/audio/cs4231a.c index 5a9be80ba3..eb916035ec 100644 --- a/hw/audio/cs4231a.c +++ b/hw/audio/cs4231a.c @@ -528,7 +528,7 @@ static int cs_write_audio (CSState *s, int nchan, int dma_pos, int dma_len, int len) { int temp, net; - uint8_t tmpbuf[4096]; + QEMU_UNINITIALIZED uint8_t tmpbuf[4096]; IsaDmaClass *k = ISADMA_GET_CLASS(s->isa_dma); temp = len; @@ -547,7 +547,7 @@ static int cs_write_audio (CSState *s, int nchan, int dma_pos, copied = k->read_memory(s->isa_dma, nchan, tmpbuf, dma_pos, to_copy); if (s->tab) { int i; - int16_t linbuf[4096]; + QEMU_UNINITIALIZED int16_t linbuf[4096]; for (i = 0; i < copied; ++i) linbuf[i] = s->tab[tmpbuf[i]]; -- 2.39.3