[RFT] llquantize for FreeBSD's dtrace

[Pedro Giffuni]

Hello Fabian;

--- Sab 23/6/12, Fabian Keil ha scritto:

> Pedro Giffuni <pfg at FreeBSD.org> wrote:
> 
> > I am not a Dtrace user (yet) but I started to port the
> Log/linear
> > quantizations from Illumos:
> > 
> > http://dtrace.org/blogs/bmc/2011/02/08/llquantize/
> > 
> > Apparently this patch should do it:
> > 
> > http://people.freebsd.org/~pfg/patches/patch-llquantize-complete
> > 
> > Unfortunately when I tried to build current with Dtrace
> > support, my i386 Virtualbox VM got stuck in ctfmerge so
> > this is completely untested.
> > 
> > Testers that know how to use it are welcome :).
> 
> I applied it on 10-CURRENT amd64 from /usr/src with patch
> -p0 without any conflicts, but it doesn't appear to be
> working.
> 
> The example from the blog post above triggers an assertion
> that is still reproducible when reducing the test case:
> 
> fk at r500 /tmp $sudo dtrace -n 'tick-1ms{@ = llquantize(i++,
> 10, 0, 6, 20);}'
> Assertion failed: (!(arg & (UINT16_MAX <<
> args[i].shift))), file
> /usr/src/cddl/lib/libdtrace/../../../cddl/contrib/opensolaris/lib/libdtrace/common/dt_cc.c,
> line 1429.
>

Thanks for testing!

It seems like the syntax has changed from the time the
example from the blog was made. The code says:

/*
 * For log/linear quantizations, we have between one and five
 * arguments in addition to the expression:
 *
 *    arg1 => Factor
 *    arg2 => Low magnitude
 *    arg3 => High magnitude
 *    arg4 => Number of steps per magnitude
 *    arg5 => Quantization increment value (defaults to 1)
 */


My suggestion would be to instead try using the test
scripts in
cddl/contrib/opensolaris/cmd/dtrace/test/tst/common/llquantize/

err.D_LLQUANT_FACTORSMALL.d (for example) has

@ = llquantize(0, 1, 0, 10, 10);

hope that helps!

Pedro.