From: Kevin O'Connor <kevin@koconnor.net>
Date: Mon, 17 Dec 2018 15:23:49 +0000 (-0500)
Subject: output: Avoid thunking to 16bit mode in printf() if no vgabios
X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=29ba89e67ff39b7673912022bf54c8640ae113cd;p=people%2Fandrewcoop%2Fseabios.git

output: Avoid thunking to 16bit mode in printf() if no vgabios

It is not necessary to call the vgabios if no vgabios has been
installed.  This reduces the amount of hardware accesses on qemu when
the bios is not initializing the display hardware, and it can reduce
the boot time by a couple of milliseconds.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
---

diff --git a/src/output.c b/src/output.c
index ec51f5e..3c335cb 100644
--- a/src/output.c
+++ b/src/output.c
@@ -74,6 +74,9 @@ static struct putcinfo debuginfo = { debug_putc };
 static void
 screenc(char c)
 {
+    if (!MODESEGMENT && GET_IVT(0x10).segoff == FUNC16(entry_10).segoff)
+        // No need to thunk to 16bit mode if vgabios is not present
+        return;
     struct bregs br;
     memset(&br, 0, sizeof(br));
     br.flags = F_IF;