On Tue, Oct 19, 2010 at 03:29:51PM +0100, Richard W.M. Jones wrote: > On Tue, Oct 19, 2010 at 03:59:36PM +0200, Jan Kiszka wrote: > > Once we have "-trace events=...", defining the list of active > > tracepoints before starting qemu will be trivial (e.g. via a config > > file). Of course, this requires that all tracepoints are built-in... > > Sorry that I've not been following this very closely, but does this > sort of thing allow tracing reads and writes to block devices? Am I > right in thinking that if a tracepoint existed in the right place, one > could get a log file from that which could be post-processed in > another tool? > > cf: > http://rwmj.wordpress.com/2010/10/05/visualizing-reads-writes-and-alignment/#content
While having a static tracepoint in the right place would be best, it is not strictly neccessary with a tool like DTrace/SystemTAP. With the qemu debuginfo available, those tools can dynamically insert a probe into any QEMU function at any point in the code. So you could easily replace your QEMU patch from that blog post with a simple trace script and get the same info dynamically. The benefit of static markers is that they can provide standard named probe point + args, which are stable long term, even as the code is re-factored/renamed/moved, etc. Regards, Daniel -- |: Red Hat, Engineering, London -o- http://people.redhat.com/berrange/ :| |: http://libvirt.org -o- http://virt-manager.org -o- http://deltacloud.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: GnuPG: 7D3B9505 -o- F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|