[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Stack calibration
Re: Stack calibration
Sat, 27 Sep 2008 19:20:32 +0100
2008/9/12 Ludovic Courtès <address@hidden>:
> That's the second important thing that should go in 1.8.6 IMO.
>> + /* x1 and x2 are the stack depth values that we get on a Debian
>> + GNU/Linux ia32 system - which we take as our canonical system.
>> + y1 and y2 are the values measured on the system where Guile is
>> + currently running. */
>> + int x1 = 170, x2 = 690, y1, y2;
> These results are dependent on what the loop in `boot-9.scm' does.
> Thus, it'd be nicer if they weren't that far away from it.
Agreed, and I think I've addressed this in my latest version (below).
> It might be worth mentioning the GCC version and optimization level that
> led to this result.
Good idea, will do. (This isn't yet in the attached patch.)
> Also, `x1' and `x2' can be made "static const" or some such.
In the new version, they are #defines.
>> + SCM_VALIDATE_INT_COPY (1, d1, y1);
>> + SCM_VALIDATE_INT_COPY (2, d2, y2);
>> + calibrated_m = ((double) (y2 - y1)) / (x2 - x1);
>> + calibrated_c = ((double) y2) - calibrated_m * x2;
> Shouldn't it be:
> calibrated_c = y1 - x1;
No, don't think so! My model equation is y = mx + c, so c = y - mx.
> Also, the computation of `calibrated_m' needs more casts to `double' I
I don't think so, and this hasn't changed in the new version. Where
and why do you think more casts are needed?
> Could it be moved to a `%print-stack-calibration' function that we'd use
> for troubleshooting?
Yes. In the attached patch, I've left this out completely, but I
think we should add it back in as %get-stack-calibration.
> How about entirely removing the startup overhead by computing the
> calibration factors only once, at installation time?
> This would mean:
> 1. Compile all of Guile with the default calibration factors (m = 1
> and c = 0).
> 2. Run a Scheme script that computes `m' and `c' and produces, say,
> `calibration.h', which is included by `stackchk.c'. Both the
> computation and the reference stack depths (`x1' and `x2' above)
> would live in this script, which is clearer IMO.
Agreed, see new libguile/calibrate.scm file.
> 3. Invoke `make' recursively, which should rebuild libguile with the
> appropriate calibration factor (typically, only `stackchk.lo' would
> need to be recompiled).
I've done this part a bit differently - see the libguile/Makefile.am
changes - because I couldn't see exactly how the recursive make
approach would work. If you think recursive make would be
significantly better, can you describe or propose the detailed changes
that would be needed?
> Also, the on-line and Texi documentation of `eval-options' must be
> updated to specify that the stack depth unit is "abstract" and
> (hopefully) portable across platforms.
I will do this (and also NEWS), but let's agree all the code first.
Many thanks for your detailed review, BTW!
Description: Text Data