On Wed, Sep 22, 2021 at 09:56:06AM +0200, Magnus Karlsson wrote:

From: Magnus Karlsson <magnus.karlsson@intel.com>

Optimize for the aligned case by precomputing the parameter values of
the xdp_buff_xsk and xdp_buff structures in the heads array. We can do
this as the heads array size is equal to the number of chunks in the
umem for the aligned case. Then every entry in this array will reflect
a certain chunk/frame and can therefore be prepopulated with the
correct values and we can drop the use of the free_heads stack. Note
that it is not possible to allocate more buffers than what has been
allocated in the aligned case since each chunk can only contain a
single buffer.

We can unfortunately not do this in the unaligned case as one chunk
might contain multiple buffers. In this case, we keep the old scheme
of populating a heads entry every time it is used and using
the free_heads stack.

Also move xp_release() and xp_get_handle() to xsk_buff_pool.h. They
were for some reason in xsk.c even though they are buffer pool
operations.

Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>

My apologies if this has already been reported (I have not seen a report
on netdev nor a report from Intel around it) but this patch as
commit 94033cd8e73b ("xsk: Optimize for aligned case") in -next causes
the following build failure with clang + x86_64 allmodconfig:

net/xdp/xsk_buff_pool.c:465:15: error: variable 'xskb' is uninitialized when used here [-Werror,-Wuninitialized]
                        xp_release(xskb);
                                   ^~~~
net/xdp/xsk_buff_pool.c:455:27: note: initialize the variable 'xskb' to silence this warning
        struct xdp_buff_xsk *xskb;
                                 ^
                                  = NULL
1 error generated.

Cheers,
Nathan