Re: [RFC PATCH v2] ptr_ring: linked list fallback

[Jason Wang]

On 2018年02月28日 12:09, Michael S. Tsirkin wrote:
Or we can add plist to a union:


struct sk_buff {
          union {
                  struct {
                          /* These two members must be first. */
                          struct sk_buff          *next;
                          struct sk_buff          *prev;
                          union {
                                  struct net_device       *dev;
                                  /* Some protocols might use this space to 
store information,
                                   * while device pointer would be NULL.
                                   * UDP receive path is one user.
                                   */
                                  unsigned long           dev_scratch;
                          };
                  };
                  struct rb_node  rbnode; /* used in netem & tcp stack */
+               struct plist plist; /* For use with ptr_ring */
          };

This look ok.

For XDP, we need to embed plist in struct xdp_buff too,
Right - that's pretty straightforward, isn't it?
Yes, it's not clear to me this is really needed for XDP consider the lock
contention it brings.

Thanks
The contention is only when the ring overflows into the list though.


Right, but there's usually a mismatch of speed between producer and 
consumer. In case of a fast producer, we may get this contention very 
frequently.

Thanks