On Wed, Jan 20, 2021 at 2:39 PM Brendan Jackman <jackmanb@xxxxxxxxxx> wrote: > > Alexei pointed out [1] that this wording is pretty confusing. Here's > an attempt to be more explicit and clear. > > [1] https://lore.kernel.org/bpf/CAADnVQJVvwoZsE1K+6qRxzF7+6CvZNzygnoBW9tZNWJELk5c=Q@xxxxxxxxxxxxxx/T/#m07264fc18fdc43af02fc1320968afefcc73d96f4 > It is common practice to use "Link: URL" to refer to other mail threads; and to use the "permalink": https://lore.kernel.org/bpf/CAADnVQJVvwoZsE1K+6qRxzF7+6CvZNzygnoBW9tZNWJELk5c=Q@xxxxxxxxxxxxxx/ which is a bit shorter than the link you provided. If you follow that convention with "Link: URL", checkpatch.pl will not complain about this long line :) Lukas > Signed-off-by: Brendan Jackman <jackmanb@xxxxxxxxxx> > --- > Documentation/networking/filter.rst | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/Documentation/networking/filter.rst b/Documentation/networking/filter.rst > index 4c2bb4c6364d..b3f457802836 100644 > --- a/Documentation/networking/filter.rst > +++ b/Documentation/networking/filter.rst > @@ -1081,9 +1081,10 @@ before is loaded back to ``R0``. > > Note that 1 and 2 byte atomic operations are not supported. > > -Except ``BPF_ADD`` *without* ``BPF_FETCH`` (for legacy reasons), all 4 byte > -atomic operations require alu32 mode. Clang enables this mode by default in > -architecture v3 (``-mcpu=v3``). For older versions it can be enabled with > +Clang can generate atomic instructions by default when ``-mcpu=v3`` is > +enabled. If a lower version for ``-mcpu`` is set, the only atomic instruction > +Clang can generate is ``BPF_ADD`` *without* ``BPF_FETCH``. If you need to enable > +the atomics features, while keeping a lower ``-mcpu`` version, you can use > ``-Xclang -target-feature -Xclang +alu32``. > > You may encounter ``BPF_XADD`` - this is a legacy name for ``BPF_ATOMIC``, > -- > 2.30.0.284.gd98b1dd5eaa7-goog >
