On Mon, 6 May 2019 16:51:57 -0700 Jakub Kicinski <jakub.kicin...@netronome.com> wrote:
> On Sun, 5 May 2019 13:36:06 +0300, Tariq Toukan wrote: > > Many device drivers use the same prefetch code structure to > > deal with small L1 cacheline size. > > Take this code into a function and call it from the drivers. > > > > Suggested-by: Jakub Kicinski <jakub.kicin...@netronome.com> > > Signed-off-by: Tariq Toukan <tar...@mellanox.com> > > Reviewed-by: Saeed Mahameed <sae...@mellanox.com> > > Cc: Jesper Dangaard Brouer <bro...@redhat.com> > > We could bike shed on the name a little - net_prefetch_headers() ? > but at least a short kdoc explanation for the purpose of this helper > would be good IMHO. I would at least improve the commit message. As Alexander so nicely explained[1], this prefetch purpose: "the 2 prefetches are needed for x86 if you want a full TCP or IPv6 header pulled into the L1 cache for instance." Although, this is not true for a minimum TCP-packet Eth(14)+IP(20)+TCP(20)=54 bytes. An I missing an alignment in my calc? [1] https://lore.kernel.org/netdev/CAKgT0UeEL3W42eDqSt97xnn3tXDtWMf4sdPByAtvbx=z7sx...@mail.gmail.com/ The name net_prefetch_headers() suggested by Jakub makes sense, as this indicate that this should be used for prefetching packet headers. As Alexander also explained, I was wrong in thinking the HW DCU (Data Cache Unit) prefetcher will fetch two cache-lines automatically. As the DCU prefetcher is a streaming prefetcher, and doesn't see our access pattern, which is why we need this. -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer
