Re: [PATCH bpf-next] selftests/bpf: add options and frags to xdp_hw_metadata

[Stanislav Fomichev <sdf@google.com>]

On 10/10, Larysa Zaremba wrote:
> On Mon, Oct 09, 2023 at 09:49:54AM -0700, Stanislav Fomichev wrote:
> > On 10/09, Larysa Zaremba wrote:
> > > This is a follow-up to the commit 9b2b86332a9b ("bpf: Allow to use kfunc
> > > XDP hints and frags together").
> > > 
> > > The are some possible implementations problems that may arise when
> > > providing metadata specifically for multi-buffer packets, therefore there
> > > must be a possibility to test such option separately.
> > > 
> > > Add an option to use multi-buffer AF_XDP xdp_hw_metadata and mark used XDP
> > > program as capable to use frags.
> > > 
> > > As for now, xdp_hw_metadata accepts no options, so add simple option
> > > parsing logic and a help message.
> > > 
> > > For quick reference, also add an ingress packet generation command to the
> > > help message. The command comes from [0].
> > > 
> > > Example of output for multi-buffer packet:
> > > 
> > > xsk_ring_cons__peek: 1
> > > 0xead018: rx_desc[15]->addr=10000000000f000 addr=f100 comp_addr=f000
> > > rx_hash: 0x5789FCBB with RSS type:0x29
> > > rx_timestamp:  1696856851535324697 (sec:1696856851.5353)
> > > XDP RX-time:   1696856843158256391 (sec:1696856843.1583)
> > > 	delta sec:-8.3771 (-8377068.306 usec)
> > > AF_XDP time:   1696856843158413078 (sec:1696856843.1584)
> > > 	delta sec:0.0002 (156.687 usec)
> > > 0xead018: complete idx=23 addr=f000
> > > xsk_ring_cons__peek: 1
> > > 0xead018: rx_desc[16]->addr=100000000008000 addr=8100 comp_addr=8000
> > > 0xead018: complete idx=24 addr=8000
> > > xsk_ring_cons__peek: 1
> > > 0xead018: rx_desc[17]->addr=100000000009000 addr=9100 comp_addr=9000 EoP
> > > 0xead018: complete idx=25 addr=9000
> > > 
> > > Metadata is printed for the first packet only.
> > > 
> > > [0] https://lore.kernel.org/all/20230119221536.3349901-18-sdf@google.com/
> > > 
> > > Signed-off-by: Larysa Zaremba <larysa.zaremba@intel.com>
> > > ---
> > >  .../selftests/bpf/progs/xdp_hw_metadata.c     |  2 +-
> > >  tools/testing/selftests/bpf/xdp_hw_metadata.c | 92 ++++++++++++++++---
> > >  2 files changed, 79 insertions(+), 15 deletions(-)
> > > 
> > > diff --git a/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c b/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
> > > index 63d7de6c6bbb..8767d919c881 100644
> > > --- a/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
> > > +++ b/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
> > > @@ -21,7 +21,7 @@ extern int bpf_xdp_metadata_rx_timestamp(const struct xdp_md *ctx,
> > >  extern int bpf_xdp_metadata_rx_hash(const struct xdp_md *ctx, __u32 *hash,
> > >  				    enum xdp_rss_hash_type *rss_type) __ksym;
> > >  
> > > -SEC("xdp")
> > > +SEC("xdp.frags")
> > >  int rx(struct xdp_md *ctx)
> > >  {
> > >  	void *data, *data_meta, *data_end;
> > > diff --git a/tools/testing/selftests/bpf/xdp_hw_metadata.c b/tools/testing/selftests/bpf/xdp_hw_metadata.c
> > > index 17c980138796..25225720346b 100644
> > > --- a/tools/testing/selftests/bpf/xdp_hw_metadata.c
> > > +++ b/tools/testing/selftests/bpf/xdp_hw_metadata.c
> > > @@ -26,6 +26,7 @@
> > >  #include <linux/sockios.h>
> > >  #include <sys/mman.h>
> > >  #include <net/if.h>
> > > +#include <ctype.h>
> > >  #include <poll.h>
> > >  #include <time.h>
> > >  
> > > @@ -49,19 +50,29 @@ struct xsk {
> > >  struct xdp_hw_metadata *bpf_obj;
> > >  struct xsk *rx_xsk;
> > >  const char *ifname;
> > > +bool use_frags;
> > >  int ifindex;
> > >  int rxq;
> > >  
> > >  void test__fail(void) { /* for network_helpers.c */ }
> > >  
> > > -static int open_xsk(int ifindex, struct xsk *xsk, __u32 queue_id)
> > > +static struct xsk_socket_config gen_socket_config(void)
> > >  {
> > > -	int mmap_flags = MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE;
> > > -	const struct xsk_socket_config socket_config = {
> > > +	struct xsk_socket_config socket_config = {
> > >  		.rx_size = XSK_RING_PROD__DEFAULT_NUM_DESCS,
> > >  		.tx_size = XSK_RING_PROD__DEFAULT_NUM_DESCS,
> > >  		.bind_flags = XDP_COPY,
> > >  	};
> > > +
> > > +	if (use_frags)
> > > +		socket_config.bind_flags |= XDP_USE_SG;
> > > +	return socket_config;
> > > +}
> > 
> > nit: why not drop const from socket_config and add this 'if (use_frags)'
> > directly to open_xsk? Not sure separate function really buys us anything?
> >
> 
> Considering there will also be ZC/copy option, I thought it would be good to 
> separate socket config creation. After giving this a sencond thought though, 
> for now options would control bind_flags only. What do you this about removing 
> gen_socket_config(), but introducing get_bind_flags()?

In my pending series [0] I ended up adding bind_flags argument
to open_xsk. Maybe do the same here? This also lets you drop
global use_frags (if you move option parsing directly into main).

Or maybe add global bind_flags if you want to keep separate parsing
routine (read_args)? Doesn't seem like we get anything by storing
separate use_flags/use_copy and then construct bind_flags via extra
get_bind_flags()?
 
0: https://lore.kernel.org/bpf/20231003200522.1914523-10-sdf@google.com/