Re: AF_XDP and dma
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
- Subject: Re: AF_XDP and dma
- From: Magnus Karlsson <magnus.karlsson@xxxxxxxxx>
- Date: Fri, 9 Apr 2021 13:06:17 +0200
- In-reply-to: <CAGZFCEGzm5M=pnuXrA5vXGfntX8BOtyVfVK2hmANVfAn7b79=Q@mail.gmail.com>
- References: <CAGZFCEHR2brK5yoMZt=GsaZtg_0XB+sb-XLz_m5WjZr9xQDP3A@mail.gmail.com> <CAJ8uoz2Kv7aQP1BoxKET+v5k9jgSgQCK38RpNp-xCzwfEKvFRA@mail.gmail.com> <CAGZFCEGDtF1SfBWEbrYG9=Na+71mJ1kk5L+9W3f-UcKjYGjLCw@mail.gmail.com> <CAJ8uoz0O2yXoA09ZNO5iviFOv-ipgaf0ZhYD=ZUb8QG7VP5Edg@mail.gmail.com> <CAGZFCEEG=r1i4PY7bT3KOTEwR1RTMeqyS31fZ+kYp_XyvaH61w@mail.gmail.com> <CAJ8uoz3ipXOE2VeMLh02R0FKysuovLf3vFU_z5nEOffHNps1=g@mail.gmail.com> <CAGZFCEGzm5M=pnuXrA5vXGfntX8BOtyVfVK2hmANVfAn7b79=Q@mail.gmail.com>
On Fri, Apr 9, 2021 at 12:50 PM ratheesh kannoth <ratheesh.ksz@xxxxxxxxx> wrote:
>
> On Fri, Apr 9, 2021 at 3:50 PM Magnus Karlsson
> <magnus.karlsson@xxxxxxxxx> wrote:
> > Then looking at user-space code will not help you :-). Take a look at
> > the code in driver/net/ethernet/intel/i40e/i40e_xsk.c in the Linux
> > kernel for an example on how to DMA map the umem.
>
> Thanks, i could see that it is pinning the pages and mapping.
>
> Using Kernel DMA api, we can map the virtual memory. But how the NIC
> can write/read to the memory if it is not physically contiguous. NIC
> card only understand physical addresses. Correct me.
In XDP/AF_XDP mode, the NIC only uses a single 4K page (on x86-64) per
packet so it will be physically contiguous by definition. Every single
page will be dma mapped separately and can reside anywhere. There is
no scatter-gather in XDP/AF_XDP mode.
> > > > > > /Magnus
[Index of Archives]
[Linux Networking Development]
[Fedora Linux Users]
[Linux SCTP]
[DCCP]
[Gimp]
[Yosemite Campsites]
