Messages in this thread Patch in this message | | | Date | Fri, 24 May 2019 13:52:31 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 00/18] locking/atomic: atomic64 type cleanup |
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On Fri, May 24, 2019 at 12:42:20PM +0100, Will Deacon wrote:
> > diff --git a/Documentation/atomic_t.txt b/Documentation/atomic_t.txt > > index dca3fb0554db..125c95ddbbc0 100644 > > --- a/Documentation/atomic_t.txt > > +++ b/Documentation/atomic_t.txt > > @@ -83,6 +83,9 @@ The non-RMW ops are (typically) regular LOADs and STOREs and are canonically > > implemented using READ_ONCE(), WRITE_ONCE(), smp_load_acquire() and > > smp_store_release() respectively. > > > > Not sure you need a new paragraph here. > > > +Therefore, if you find yourself only using the Non-RMW operations of atomic_t, > > +you do not in fact need atomic_t at all and are doing it wrong. > > + > > That makes sense to me, although I now find that the sentence below is a bit > confusing because it sounds like it's a caveat relating to only using > Non-RMW ops. > > > The one detail to this is that atomic_set{}() should be observable to the RMW > > ops. That is: > > How about changing this to be: > > "A subtle detail of atomic_set{}() is that it should be observable..."
Done, find below.
--- Subject: Documentation/atomic_t.txt: Clarify pure non-rmw usage
Clarify that pure non-RMW usage of atomic_t is pointless, there is nothing 'magical' about atomic_set() / atomic_read().
This is something that seems to confuse people, because I happen upon it semi-regularly.
Acked-by: Will Deacon <will.deacon@arm.com> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- Documentation/atomic_t.txt | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/Documentation/atomic_t.txt b/Documentation/atomic_t.txt index dca3fb0554db..89eae7f6b360 100644 --- a/Documentation/atomic_t.txt +++ b/Documentation/atomic_t.txt @@ -81,9 +81,11 @@ SEMANTICS The non-RMW ops are (typically) regular LOADs and STOREs and are canonically implemented using READ_ONCE(), WRITE_ONCE(), smp_load_acquire() and -smp_store_release() respectively. +smp_store_release() respectively. Therefore, if you find yourself only using +the Non-RMW operations of atomic_t, you do not in fact need atomic_t at all +and are doing it wrong. -The one detail to this is that atomic_set{}() should be observable to the RMW +A subtle detail of atomic_set{}() is that it should be observable to the RMW ops. That is: C atomic-set
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