netdev - Re: [PATCH bpf-next 10/14] mlx5, xsk: migrate to new MEM_TYPE_XSK_BUFF

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Date:   Fri, 8 May 2020 15:08:38 +0200
From:   Björn Töpel <bjorn.topel@...il.com>
To:     Maxim Mikityanskiy <maximmi@...lanox.com>
Cc:     Björn Töpel <bjorn.topel@...el.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        "Fijalkowski, Maciej" <maciej.fijalkowski@...el.com>
Subject: Re: [PATCH bpf-next 10/14] mlx5, xsk: migrate to new MEM_TYPE_XSK_BUFF_POOL

On Fri, 8 May 2020 at 15:01, Maxim Mikityanskiy <maximmi@...lanox.com> wrote:
>
> On 2020-05-08 15:27, Björn Töpel wrote:
> > On 2020-05-08 13:55, Maxim Mikityanskiy wrote:
> >> On 2020-05-07 13:42, Björn Töpel wrote:
> >>> From: Björn Töpel <bjorn.topel@...el.com>
> >>>
> >>> Use the new MEM_TYPE_XSK_BUFF_POOL API in lieu of MEM_TYPE_ZERO_COPY in
> >>> mlx5e. It allows to drop a lot of code from the driver (which is now
> >>> common in AF_XDP core and was related to XSK RX frame allocation, DMA
> >>> mapping, etc.) and slightly improve performance.
> >>>
> >>> rfc->v1: Put back the sanity check for XSK params, use XSK API to get
> >>>           the total headroom size. (Maxim)
> >>>
> >>> Signed-off-by: Björn Töpel <bjorn.topel@...el.com>
> >>> Signed-off-by: Maxim Mikityanskiy <maximmi@...lanox.com>
> >>
> >> I did some functional and performance tests.
> >>
> >> Unfortunately, something is wrong with the traffic: I get zeros in
> >> XDP_TX, XDP_PASS and XSK instead of packet data. I set DEBUG_HEXDUMP
> >> in xdpsock, and it shows the packets of the correct length, but all
> >> bytes are 0 after these patches. It might be wrong xdp_buff pointers,
> >> however, I still have to investigate it. Björn, does it also affect
> >> Intel drivers, or is it Mellanox-specific?
> >>
> >
> > Are you getting zeros for TX, PASS *and* in xdpsock (REDIRECT:ed
> > packets), or just TX and PASS?
>
> Yes, in all modes: XDP_TX, XDP_PASS and XDP_REDIRECT to XSK (xdpsock).
>
> > No, I get correct packet data for AF_XDP zero-copy XDP_REDIRECT,
> > XDP_PASS, and XDP_TX for Intel.
>
> Hmm, weird - with the new API I expected the same behavior on all
> drivers. Thanks for the information, I'll know that I need to look in
> mlx5 code to find the issue.
>

All zeros hints that you're probably putting in the wrong DMA address somewhere.

> >> For performance, I got +1.0..+1.2 Mpps on RX. TX performance got
> >> better after Björn inlined the relevant UMEM functions, however, there
> >> is still a slight decrease compared to the old code. I'll try to find
> >> the possible reason, but the good thing is that it's not significant
> >> anymore.
> >>
> >
> > Ok, so for Rx mlx5 it's the same as for i40e. Good! :-)
> >
> > How much decrease on Tx?
>
> ~0.8 Mpps (was 3.1 before you inlined the functions).
>

Thanks. Still a bit much. What does perf say?


Björn