* Byungchul Park <[email protected]> wrote:
> On Thu, Oct 19, 2017 at 03:11:12PM +0900, Byungchul Park wrote:
> > On Thu, Oct 19, 2017 at 07:57:30AM +0200, Ingo Molnar wrote:
> > >
> > > * Byungchul Park <[email protected]> wrote:
> > >
> > > > On Wed, Oct 18, 2017 at 12:09:44PM +0200, Ingo Molnar wrote:
> > > > > BTW., have you attempted limiting the depth of the stack traces? I
> > > > > suspect more
> > > > > than 2-4 are rarely required to disambiguate the calling context.
> > > >
> > > > I did it for you. Let me show you the result.
> > > >
> > > > 1. No lockdep: 2.756558155 seconds time
> > > > elapsed ( +- 0.09% )
> > > > 2. Lockdep: 2.968710420 seconds
> > > > time elapsed ( +- 0.12% )
> > > > 3. Lockdep + Crossrelease 5 entries: 3.153839636 seconds
> > > > time elapsed ( +- 0.31% )
> > > > 4. Lockdep + Crossrelease 3 entries: 3.137205534 seconds
> > > > time elapsed ( +- 0.87% )
> > > > 5. Lockdep + Crossrelease + This patch: 2.963669551 seconds time
> > > > elapsed ( +- 0.11% )
> > >
> > > I think the lockdep + crossrelease + full-stack numbers are missing?
> >
> > Ah, the last version of crossrelease merged into vanilla, records 5
> > entries, since I thought it overloads too much if full stack is used,
> > and 5 entries are enough. Don't you think so?
> >
> > > But yeah, looks like single-entry-stacktrace crossrelease only has a
> > > +0.2%
> > > performance cost (with 0.1% noise), while lockdep itself has a +7.7% cost.
> > >
> > > That's very reasonable and we can keep the single-entry cross-release
> > > feature
> > > enabled by default as part of CONFIG_PROVE_LOCKING=y - assuming all the
> > > crashes
> >
> > BTW, is there any crash by cross-release I don't know? Of course, I know
> > cases of false positives, but I don't about crash.
>
> Are you talking about the oops by 'null pointer dereference' by unwinder a
> few weeks ago?
>
> At the time, cross-release was falsely accused. AFAIK, cross-release has
> not crashed system yet.
I'm talking about the crash fixed here:
8b405d5c5d09: locking/lockdep: Fix stacktrace mess
Which was introduced by your patch:
ce07a9415f26: locking/lockdep: Make check_prev_add() able to handle external
stack_trace
... which was a preparatory patch for cross-release. So 'technically' it's not
a
cross-release crash, but was very much related. It even says so in the
changelog:
Actually crossrelease needs to do other than saving a stack_trace.
So pass a stack_trace and callback to handle it, to check_prev_add().
... so let's not pretend it wasn't related, ok?
Thanks,
Ingo
