lkml.org 
[lkml]   [2022]   [Mar]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 16/19] context_tracking: Convert state to atomic_t
On Sat, Mar 12, 2022 at 11:54:09PM +0100, Peter Zijlstra wrote:
> On Wed, Mar 02, 2022 at 04:48:07PM +0100, Frederic Weisbecker wrote:
> > +static __always_inline int __ct_state(void)
> > +{
> > + return atomic_read(this_cpu_ptr(&context_tracking.state));
> > +}
>
> One arguably horrible thing to do would be to write it like:
>
> return __this_cpu_read(context_tracking.state.counter);
>
> IIRC that will actually DTRT since atomic_read() is basically defined to
> be READ_ONCE() and this_cpu_read() implies the same.
>
> Only PowerPC and s390 implement arch_atomic_read() in asm, but I don't
> think they have a particularly good reason to. The only other weird case
> is Alpha, where READ_ONCE() implies smp_mb() because Alpha. I'm not sure
> we care about that case, hmm?

If we don't care about the dependency ordering, then __READ_ONCE() is the
chappy to use if the types don't get in the way too much.

Will

\
 
 \ /
  Last update: 2022-03-21 14:36    [W:0.839 / U:0.296 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site