On 5/7/2019 1:08 PM, Jesper Dangaard Brouer wrote: > 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. >
Thanks all for your comments. I will fix and re-spin once the window re-opens. Tariq
