Alexander Lobakin <aleksander.lobakin@xxxxxxxxx> writes: > Add a function to get an array of skbs from the NAPI percpu cache. > It's supposed to be a drop-in replacement for > kmem_cache_alloc_bulk(skbuff_head_cache, GFP_ATOMIC) and > xdp_alloc_skb_bulk(GFP_ATOMIC). The difference (apart from the > requirement to call it only from the BH) is that it tries to use > as many NAPI cache entries for skbs as possible, and allocate new > ones only if needed. > > The logic is as follows: > > * there is enough skbs in the cache: decache them and return to the > caller; > * not enough: try refilling the cache first. If there is now enough > skbs, return; > * still not enough: try allocating skbs directly to the output array > with %GFP_ZERO, maybe we'll be able to get some. If there's now > enough, return; > * still not enough: return as many as we were able to obtain. > > Most of times, if called from the NAPI polling loop, the first one will > be true, sometimes (rarely) the second one. The third and the fourth -- > only under heavy memory pressure. > It can save significant amounts of CPU cycles if there are GRO cycles > and/or Tx completion cycles (anything that descends to > napi_skb_cache_put()) happening on this CPU. > > Signed-off-by: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx> > Tested-by: Daniel Xu <dxu@xxxxxxxxx> Neat idea! Reviewed-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
