On Wed, 10 Feb 2021 16:30:23 +0000 Alexander Lobakin <aloba...@pm.me> wrote:
> Instead of just bulk-flushing skbuff_heads queued up through > napi_consume_skb() or __kfree_skb_defer(), try to reuse them > on allocation path. Maybe you are already aware of this dynamics, but high speed NICs will usually run the TX "cleanup" (opportunistic DMA-completion) in the napi poll function call, and often before processing RX packets. Like ixgbe_poll[1] calls ixgbe_clean_tx_irq() before ixgbe_clean_rx_irq(). If traffic is symmetric (or is routed-back same interface) then this SKB recycle scheme will be highly efficient. (I had this part of my initial patchset and tested it on ixgbe). [1] https://elixir.bootlin.com/linux/v5.11-rc7/source/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c#L3149 > If the cache is empty on allocation, bulk-allocate the first > 16 elements, which is more efficient than per-skb allocation. > If the cache is full on freeing, bulk-wipe the second half of > the cache (32 elements). > This also includes custom KASAN poisoning/unpoisoning to be > double sure there are no use-after-free cases. > > To not change current behaviour, introduce a new function, > napi_build_skb(), to optionally use a new approach later > in drivers. > > Note on selected bulk size, 16: > - this equals to XDP_BULK_QUEUE_SIZE, DEV_MAP_BULK_SIZE > and especially VETH_XDP_BATCH, which is also used to > bulk-allocate skbuff_heads and was tested on powerful > setups; > - this also showed the best performance in the actual > test series (from the array of {8, 16, 32}). > > Suggested-by: Edward Cree <ecree.xil...@gmail.com> # Divide on two halves > Suggested-by: Eric Dumazet <eduma...@google.com> # KASAN poisoning > Cc: Dmitry Vyukov <dvyu...@google.com> # Help with KASAN > Cc: Paolo Abeni <pab...@redhat.com> # Reduced batch size > Signed-off-by: Alexander Lobakin <aloba...@pm.me> > --- > include/linux/skbuff.h | 2 + > net/core/skbuff.c | 94 ++++++++++++++++++++++++++++++++++++------ > 2 files changed, 83 insertions(+), 13 deletions(-) > > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h > index 0e0707296098..906122eac82a 100644 > --- a/include/linux/skbuff.h > +++ b/include/linux/skbuff.h > @@ -1087,6 +1087,8 @@ struct sk_buff *build_skb(void *data, unsigned int > frag_size); > struct sk_buff *build_skb_around(struct sk_buff *skb, > void *data, unsigned int frag_size); > > +struct sk_buff *napi_build_skb(void *data, unsigned int frag_size); > + > /** > * alloc_skb - allocate a network buffer > * @size: size to allocate > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > index 860a9d4f752f..9e1a8ded4acc 100644 > --- a/net/core/skbuff.c > +++ b/net/core/skbuff.c > @@ -120,6 +120,8 @@ static void skb_under_panic(struct sk_buff *skb, unsigned > int sz, void *addr) > } > > #define NAPI_SKB_CACHE_SIZE 64 > +#define NAPI_SKB_CACHE_BULK 16 > +#define NAPI_SKB_CACHE_HALF (NAPI_SKB_CACHE_SIZE / 2) > -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer
