[Qemu-devel] [PATCH] Remove line buffering from log file

[Peter Chubb <peter.chubb@nicta.com.au>]

This patch was originally written by Bernard Blackham, and modified by
Peter Chubb.

From 0d755af2f5bef22432da71f2fe0a9dce7d2882cd Mon Sep 17 00:00:00 2001
From: Bernard Blackham <bernard.blackham@nicta.com.au>
Date: Fri, 24 Jul 2009 13:38:03 +1000
Subject: Disable line-based log buffering. 

There's no real reason for line-based buffering in log file output.
If block buffering with a decent sized buffer is used, it can speed 
qemu up for -d all or -d exec significantly. 

The only thing you lose is that the last up to 4k of log output may be lost if
qemu crashes.

Signed-off-by: Peter Chubb <peter.chubb@nicta.com.au>
Signed-off-by: Hans Jang <hsjang@ok-labs.com>
Signed-off-by: Bernard Blackham <bernard.blackham@nicta.com.au>
---
 exec.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

Index: qemu-working/exec.c
===================================================================
--- qemu-working.orig/exec.c	2011-09-29 09:03:35.866233828 +1000
+++ qemu-working/exec.c	2011-09-29 12:40:56.668973550 +1000
@@ -1594,29 +1594,28 @@ void cpu_single_step(CPUState *env, int
 /* enable or disable low levels log */
 void cpu_set_log(int log_flags)
 {
     loglevel = log_flags;
     if (loglevel && !logfile) {
         logfile = fopen(logfilename, log_append ? "a" : "w");
         if (!logfile) {
             perror(logfilename);
             _exit(1);
         }
+
+/* Don't use line-based buffering: it hurts -d exec */
 #if !defined(CONFIG_SOFTMMU)
         /* must avoid mmap() usage of glibc by setting a buffer "by hand" */
         {
             static char logfile_buf[4096];
-            setvbuf(logfile, logfile_buf, _IOLBF, sizeof(logfile_buf));
+            setvbuf(logfile, logfile_buf, _IOFBF, sizeof(logfile_buf));
         }
-#elif !defined(_WIN32)
-        /* Win32 doesn't support line-buffering and requires size >= 2 */
-        setvbuf(logfile, NULL, _IOLBF, 0);
 #endif
         log_append = 1;
     }
     if (!loglevel && logfile) {
         fclose(logfile);
         logfile = NULL;
     }
 }
 
 void cpu_set_log_filename(const char *filename)

--
Dr Peter Chubb  http://www.gelato.unsw.edu.au  peterc AT gelato.unsw.edu.au
http://www.ertos.nicta.com.au           ERTOS within National ICT Australia