| Message ID | 20210120133946.2107897-3-jackmanb@google.com (mailing list archive) |
|---|---|
| State | Accepted |
| Delegated to: | BPF |
| Headers | show |
| Series | BPF docs fixups | expand |
| Context | Check | Description |
|---|---|---|
| netdev/apply | success | Patch already applied to bpf-next |
| netdev/tree_selection | success | Clearly marked for bpf-next |
On Wed, Jan 20, 2021 at 11:57 AM Lukas Bulwahn <lukas.bulwahn@gmail.com> wrote: > > On Wed, Jan 20, 2021 at 2:39 PM Brendan Jackman <jackmanb@google.com> 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@mail.gmail.com/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@mail.gmail.com/ > > which is a bit shorter than the link you provided. I fixed it up while applying. Thanks everyone.
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``,
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@mail.gmail.com/T/#m07264fc18fdc43af02fc1320968afefcc73d96f4 Signed-off-by: Brendan Jackman <jackmanb@google.com> --- Documentation/networking/filter.rst | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)