Re: [PATCH v2] locking/rwsem: Add __always_inline annotation to __down_read_common()

[John Stultz]

On Mon, Apr 17, 2023 at 1:19 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> On Wed, Apr 12, 2023 at 03:59:05AM +0000, John Stultz wrote:
> > Apparently despite it being marked inline, the compiler
> > may not inline __down_read_common() which makes it difficult
> > to identify the cause of lock contention, as the blocked
> > function will always be listed as __down_read_common().
> >
> > So this patch adds __always_inline annotation to the
> > function to force it to be inlines so the calling function
> > will be listed.
>
> I'm a wee bit confused; what are you looking at? Wchan?

Apologies! Yes, traceevent data via wchan, sorry I didn't make that clear.

> What is stopping
> the compiler from now handing you
> __down_read{,_interruptible,_killable}() instead? Is that fine?

No, we want to make the blocked calling function, rather than the
locking functions, visible in the tracepoints captured. That said, the
other __down_read* functions seem to be properly inlined in practice
(Waiman's theory as to why sounds convincing to me).

If you'd like I can add those as well to be always_inline, as well so
it's more consistent?

thanks
-john