[Mono-dev] [PATCH] Mono DTrace provider

[Andreas Färber]

Hello,

Thanks for your comments.

Am 27.05.2008 um 17:24 schrieb Miguel de Icaza:

> I believe that we should
> auto-detect whether dtrace is installed instead of forcing people to
> manually enable it on platforms that support it.

The reason I did this is two-fold:

i) A static probe has a performance impact even when the probe itself  
is not enabled. It's small, somewhere in the order of five nop  
instructions, I read for Solaris 10. On OSX the header file has one  
function call (and there is no postprocessing step to change this).  
Didn't do any benchmarks myself though.
If we later add further static probes on "hot" paths such as JIT  
method compilation, I thought some people would not want to have that  
feature enabled if they know they'd not use it. But you're right, if  
anyone is so worried about performance they could of course explicitly  
use --disable-dtrace.

ii) I consider the build process changes for Solaris somewhat fragile  
and unportable, and therefore didn't want to enable them by default to  
not mess default builds of any upcoming release. We could resort to  
adding DTrace support only for Mac OS X for now if you dislike the  
changes and have no better idea. (I don't know about FreeBSD or QNX,  
it could be that they require similar postprocessing steps as Solaris  
since they all use ELF.)

A third issue for automatically enabling it would be how to correctly  
detect DTrace availability. Some Linux distros were reported to ship a  
dtrace tool which is an ISDN tracer and totally unrelated to Sun's  
DTrace. Checking for the sys/sdt.h header might be a better heuristic,  
but I don't know.

Andreas