>>>>> "Stefan" == Stefan Weil <w...@mail.berlios.de> writes:
Stefan> Am 29.09.2011 04:43, schrieb Peter Chubb: >> >> 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.black...@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. Stefan> That's the reason why line buffering is needed today. I Stefan> enable log file output to see what happened last before the Stefan> crash. Thanks for this, I didn't think of this use-case. I don't think I've ever seen a qemu crash that wasn't caused by something really obvious. Stefan> It might be possible to use buffered output with a new Stefan> function qemu_abort() which replaces the existing calls of Stefan> abort(). This function could call flush() for the log output Stefan> before aborting. In addition, SIGSEGV needs to be catched, Stefan> and the signal handler would have to call flush(), too (is Stefan> that possible in signal handlers?). abort() already flushes all open streams. So only signals that cause immediate death are a problem: SIGSEGV is the obvious one. If its handler called abort() then that would flush too. abort() is guaranteed by the POSIX spec to be callable from a signal handler. I'll experiment by adding such a handler and see what happens. Do you have a test case that causes a SEGV? Stefan> Speed is not the primary target when somebody runs qemu -d ... It is if it takes hours to reach the problem that causes the abort(). Speeding up by an order of magnitude is worth it. -- 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
