Skip automatic zero-init of large arrays / structs in I/O paths

[PATCH 20/31] hw/net/tulip: skip automatic zero-init of large array

Daniel P. Berrangé posted 31 patches 5 months, 1 week ago

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Maintainers: Kevin Wolf <kwolf@redhat.com>, Hanna Reitz <hreitz@redhat.com>, "Marc-André Lureau" <marcandre.lureau@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Gerd Hoffmann <kraxel@redhat.com>, Halil Pasic <pasic@linux.ibm.com>, Christian Borntraeger <borntraeger@linux.ibm.com>, Thomas Huth <thuth@redhat.com>, Dmitry Fleytman <dmitry.fleytman@gmail.com>, Alistair Francis <alistair@alistair23.me>, "Edgar E. Iglesias" <edgar.iglesias@gmail.com>, Peter Maydell <peter.maydell@linaro.org>, "Cédric Le Goater" <clg@kaod.org>, Steven Lee <steven_lee@aspeedtech.com>, Troy Lee <leetroy@gmail.com>, Jamin Lin <jamin_lin@aspeedtech.com>, Andrew Jeffery <andrew@codeconstruct.com.au>, Joel Stanley <joel@jms.id.au>, Jason Wang <jasowang@redhat.com>, Sven Schnelle <svens@stackframe.org>, "Michael S. Tsirkin" <mst@redhat.com>, Rob Herring <robh@kernel.org>, Keith Busch <kbusch@kernel.org>, Klaus Jensen <its@irrelevant.dk>, Jesper Devantier <foss@defmacro.it>, Nicholas Piggin <npiggin@gmail.com>, "Frédéric Barrat" <fbarrat@linux.ibm.com>, Daniel Henrique Barboza <danielhb413@gmail.com>, Harsh Prateek Bora <harshpb@linux.ibm.com>, Fam Zheng <fam@euphon.net>, Hannes Reinecke <hare@suse.com>, Jeuk Kim <jeuk20.kim@samsung.com>

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[PATCH 20/31] hw/net/tulip: skip automatic zero-init of large array

Posted by Daniel P. Berrangé 5 months, 1 week ago

The 'tulip_setup_frame' method has a 4k byte array used for copynig
DMA data from the 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 from the
device.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 hw/net/tulip.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/net/tulip.c b/hw/net/tulip.c
index 63fe513458..319af906c8 100644
--- a/hw/net/tulip.c
+++ b/hw/net/tulip.c
@@ -629,7 +629,7 @@ static void tulip_setup_filter_addr(TULIPState *s, uint8_t *buf, int n)
 static void tulip_setup_frame(TULIPState *s,
         struct tulip_descriptor *desc)
 {
-    uint8_t buf[4096];
+    QEMU_UNINITIALIZED uint8_t buf[4096];
     int len = (desc->control >> TDES1_BUF1_SIZE_SHIFT) & TDES1_BUF1_SIZE_MASK;
     int i;
 
-- 
2.49.0