On Tue, Oct 19, 2010 at 03:08:08PM +0200, Jan Kiszka wrote: > Hi Stefan, > > just had a closer look at qemu's new tracing framework. Looks cool, > though it leaves a bit room for improvements. ;) > > One quirk I stumbled over quickly was the "disable" tag in trace-events. > It confused me first as qemu starts without any tracepoint enabled by > default and I thought I had to hack the file. Then I read the doc and > wondered which exiting or future backend would come without sufficiently > fast dynamic tracepoint control. Do you have any in mind? > > Instead of making it a compile-time switch (except for simpletrace), I > would vote for declaring the simpletrace usage as the only one: disable > sets the default state of the dynamic tracepoint. That way we could use > trace-events to define a useful set of standard, moderate-impact > tracepoints that shall be on. Others will still be available once a > backend is configured, but remain off until enabled during runtime. > Anything else looks like overkill to me.
FYI with the DTrace/SystemTAP backend I posted yesterday, the 'disable' keyword is effectively completely ignored. All tracepoints are disabled when QEMU is running normally. Only when a end user runs a dtrace script that references a QEMU tracepoint, is that specific tracepoint enabled. 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 :|
