From 277dbec12b1a109aca6cfe65046f2b4d6b41ee43 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= Date: Tue, 10 Jun 2025 13:36:53 +0100 Subject: [PATCH 23/43] hw/dma/xlnx_csu_dma: 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: [15/31] 8832791cb87b342e3b9882893891a824d31b687a (stefanha/centos-stream-qemu-kvm) The 'xlnx_csu_dma_src_notify' method has a 4k byte array used for copying DMA data. 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 data is copied. Signed-off-by: Daniel P. Berrangé Reviewed-by: Stefan Hajnoczi Message-id: 20250610123709.835102-16-berrange@redhat.com Signed-off-by: Stefan Hajnoczi (cherry picked from commit ce14f24611aa0469b464a9512e192b4fd51dca2b) Signed-off-by: Stefan Hajnoczi --- hw/dma/xlnx_csu_dma.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/hw/dma/xlnx_csu_dma.c b/hw/dma/xlnx_csu_dma.c index 1afaa0bf51..8091a785cc 100644 --- a/hw/dma/xlnx_csu_dma.c +++ b/hw/dma/xlnx_csu_dma.c @@ -287,7 +287,7 @@ static uint32_t xlnx_csu_dma_advance(XlnxCSUDMA *s, uint32_t len) static void xlnx_csu_dma_src_notify(void *opaque) { XlnxCSUDMA *s = XLNX_CSU_DMA(opaque); - unsigned char buf[4 * 1024]; + QEMU_UNINITIALIZED unsigned char buf[4 * 1024]; size_t rlen = 0; ptimer_transaction_begin(s->src_timer); -- 2.39.3