Re: [RFC 00/12] locking: Separate lock tracepoints from lockdep/lock_stat (v1)

Namhyung Kim
2022-02-10T02:02:42Z

On Wed, Feb 9, 2022 at 1:09 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Tue, Feb 08, 2022 at 10:41:56AM -0800, Namhyung Kim wrote:
>
> > Eventually I'm mostly interested in the contended locks only and I
> > want to reduce the overhead in the fast path. By moving that, it'd be
> > easy to track contended locks with timing by using two tracepoints.
>
> So why not put in two new tracepoints and call it a day?
>
> Why muck about with all that lockdep stuff just to preserve the name
> (and in the process continue to blow up data structures etc..). This
> leaves distros in a bind, will they enable this config and provide
> tracepoints while bloating the data structures and destroying things
> like lockref (which relies on sizeof(spinlock_t)), or not provide this
> at all.

If it's only lockref, is it possible to change it to use arch_spinlock_t
so that it can remain in 4 bytes? It'd be really nice if we can keep
spin lock size, but it'd be easier to carry the name with it for
analysis IMHO.

Thanks,
Namhyung