From:   Jesper Dangaard Brouer <jbrouer@redhat.com>
Message-ID: <73b5076c-335b-c746-b227-0edd40435ef5@redhat.com>
Date:   Thu, 9 Mar 2023 17:43:51 +0100
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Cc:     brouer@redhat.com,
        Maciej Fijalkowski <maciej.fijalkowski@intel.com>,
        Larysa Zaremba <larysa.zaremba@intel.com>,
        =?UTF-8?Q?Toke_H=c3=b8iland-J=c3=b8rgensen?= <toke@redhat.com>,
        Song Liu <song@kernel.org>,
        Jesper Dangaard Brouer <hawk@kernel.org>,
        Menglong Dong <imagedong@tencent.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Eric Dumazet <edumazet@google.com>, bpf@vger.kernel.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH bpf-next v2 0/3] xdp: recycle Page Pool backed skbs built
 from XDP frames
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To:     Alexander Lobakin <aleksander.lobakin@intel.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <martin.lau@linux.dev>
References: <20230303133232.2546004-1-aleksander.lobakin@intel.com>
In-Reply-To: <20230303133232.2546004-1-aleksander.lobakin@intel.com>
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On 03/03/2023 14.32, Alexander Lobakin wrote:
> Yeah, I still remember that "Who needs cpumap nowadays" (c), but anyway.
> 
> __xdp_build_skb_from_frame() missed the moment when the networking stack
> became able to recycle skb pages backed by a page_pool. This was making
> e.g. cpumap redirect even less effective than simple %XDP_PASS. veth was
> also affected in some scenarios.
> A lot of drivers use skb_mark_for_recycle() already, it's been almost
> two years and seems like there are no issues in using it in the generic
> code too. {__,}xdp_release_frame() can be then removed as it losts its
> last user.
> Page Pool becomes then zero-alloc (or almost) in the abovementioned
> cases, too. Other memory type models (who needs them at this point)
> have no changes.
> 
> Some numbers on 1 Xeon Platinum core bombed with 27 Mpps of 64-byte
> IPv6 UDP, iavf w/XDP[0] (CONFIG_PAGE_POOL_STATS is enabled):
> 
> Plain %XDP_PASS on baseline, Page Pool driver:
> 
> src cpu Rx     drops  dst cpu Rx
>    2.1 Mpps       N/A    2.1 Mpps
> 
> cpumap redirect (w/o leaving its node) on baseline:

What does it mean "without leaving its node" ?
I interpret this means BPF program CPU redirect to "same" CPU ?
Or does the "node" reference a NUMA node?

> 
>    6.8 Mpps  5.0 Mpps    1.8 Mpps
> 
> cpumap redirect with skb PP recycling:

Does this test use two CPUs?

> 
>    7.9 Mpps  5.7 Mpps    2.2 Mpps
>                         +22% (from cpumap redir on baseline)
> [0] https://github.com/alobakin/linux/commits/iavf-xdp
> 
> Alexander Lobakin (3):
>    net: page_pool, skbuff: make skb_mark_for_recycle() always available
>    xdp: recycle Page Pool backed skbs built from XDP frames
>    xdp: remove unused {__,}xdp_release_frame()
> 
>   include/linux/skbuff.h |  4 ++--
>   include/net/xdp.h      | 29 -----------------------------
>   net/core/xdp.c         | 19 ++-----------------
>   3 files changed, 4 insertions(+), 48 deletions(-)
> 
> ---
>  From v1[1]:
> * make skb_mark_for_recycle() always available, otherwise there are build
>    failures on non-PP systems (kbuild bot);
> * 'Page Pool' -> 'page_pool' when it's about a page_pool instance, not
>    API (Jesper);
> * expanded test system info a bit in the cover letter (Jesper).
> 
> [1] https://lore.kernel.org/bpf/20230301160315.1022488-1-aleksander.lobakin@intel.com