Re: [PATCH 10/10] fault injection: inject faults in new/rare callchains

[Vegard Nossum]

Hi,

On 08/08/2016 03:54 PM, Akinobu Mita wrote:
> 2016-08-04 0:05 GMT+09:00 Vegard Nossum <vegard.nossum@xxxxxxxxxx>:
> > Before this patch, fault injection uses a combination of randomness and
> > frequency to determine where to inject faults. The problem with this is
> > that code paths which are executed very rarely get proportional amounts
> > of faults injected.
> >
> > A better heuristic is to look at the actual callchain leading up to the
> > possible failure point; if we see a callchain that we've never seen up
> > until this point, chances are it's a rare one and we should definitely
> > inject a fault here (since we might not get the chance again later).
> >
> > This uses a probabilistic set structure (similar to a bloom filter) to
> > determine whether we have seen a particular callchain before by hashing
> > the stack trace and atomically testing/setting a bit corresponding to
> > the current callchain.
[...]

> > +config FAULT_INJECTION_AT_NEW_CALLSITES
> > +       bool "Inject fault the first time at a new callsite"
>
> Isn't it better to make a run time configurable option instead of the
> build option?

I prefer a build option personally since it keeps the code simple (you
don't have to dynamically allocate the bitmap of known callchains, for
example). I figured most people using fault injection would enable the
new option while still allowing others to keep the current behaviour
if they really want to.

If you prefer a run-time option I can submit a new version.

Thanks,


Vegard