From cc173deaaa4d9dc6ad9188e0b03f46b7e64f26b2 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= Date: Tue, 10 Jun 2025 13:36:57 +0100 Subject: [PATCH 45/57] hw/net/rtl8139: 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: 382: Solve -ftrivial-auto-var-init performance regression with QEMU_UNINITIALIZED RH-Jira: RHEL-99888 RH-Acked-by: Miroslav Rezanina RH-Commit: [19/30] 344c720aef2feb35f84fd4b21f2b1b31e5572286 (stefanha/centos-stream-qemu-kvm) The 'rtl8139_transmit_one' method has a 8k byte array used for copying data between guest and host. Skip the automatic zero-init of this array to eliminate the performance overhead in the I/O hot path. The 'txbuffer' will be fully initialized when reading PCI DMA buffers. Signed-off-by: Daniel P. Berrangé Reviewed-by: Stefan Hajnoczi Message-id: 20250610123709.835102-20-berrange@redhat.com Signed-off-by: Stefan Hajnoczi (cherry picked from commit 3ccc6489dd4925ddd1f3066bd3751389169cd7aa) Signed-off-by: Stefan Hajnoczi --- hw/net/rtl8139.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/hw/net/rtl8139.c b/hw/net/rtl8139.c index f2fe057535..a2732bf1c1 100644 --- a/hw/net/rtl8139.c +++ b/hw/net/rtl8139.c @@ -1818,7 +1818,7 @@ static int rtl8139_transmit_one(RTL8139State *s, int descriptor) PCIDevice *d = PCI_DEVICE(s); int txsize = s->TxStatus[descriptor] & 0x1fff; - uint8_t txbuffer[0x2000]; + QEMU_UNINITIALIZED uint8_t txbuffer[0x2000]; DPRINTF("+++ transmit reading %d bytes from host memory at 0x%08x\n", txsize, s->TxAddr[descriptor]); -- 2.39.3