2016-08-08 23:07 GMT+09:00 Vegard Nossum <[email protected]>: > Hi, > > On 08/08/2016 03:54 PM, Akinobu Mita wrote: >> >> 2016-08-04 0:05 GMT+09:00 Vegard Nossum <[email protected]>: >>> >>> 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. >
I prefer run-time tunable like "/sys/kernel/debug/fail*/inject-at-new-callsites" in order to turn on or off this feature for each fault injection type. I think this doesn't add too much complexity if the bitmap can be put into struct fault_attr.
