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 14:27:08 +0200
From:   Björn Töpel <bjorn.topel@...el.com>
To:     Maxim Mikityanskiy <maximmi@...lanox.com>,
        Björn Töpel <bjorn.topel@...il.com>
Cc:     ast@...nel.org, daniel@...earbox.net, davem@...emloft.net,
        kuba@...nel.org, hawk@...nel.org, john.fastabend@...il.com,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        magnus.karlsson@...el.com, jonathan.lemon@...il.com,
        jeffrey.t.kirsher@...el.com, maciej.fijalkowski@...el.com
Subject: Re: [PATCH bpf-next 10/14] mlx5, xsk: migrate to new
 MEM_TYPE_XSK_BUFF_POOL

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?

No, I get correct packet data for AF_XDP zero-copy XDP_REDIRECT,
XDP_PASS, and XDP_TX for Intel.

> 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?


Björn