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From: Alexander Lobakin <aleksander.lobakin@intel.com>
To: Jesper Dangaard Brouer <jbrouer@redhat.com>,
	Daniel Borkmann <daniel@iogearbox.net>
Cc: brouer@redhat.com, Larysa Zaremba <larysa.zaremba@intel.com>,
	bpf@vger.kernel.org, Stanislav Fomichev <sdf@google.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Andrii Nakryiko <andrii@kernel.org>,
	Jakub Kicinski <kuba@kernel.org>,
	Martin KaFai Lau <martin.lau@linux.dev>,
	Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@kernel.org>, Jiri Olsa <jolsa@kernel.org>,
	Jesse Brandeburg <jesse.brandeburg@intel.com>,
	Tony Nguyen <anthony.l.nguyen@intel.com>,
	Anatoly Burakov <anatoly.burakov@intel.com>,
	Alexander Lobakin <alexandr.lobakin@intel.com>,
	Magnus Karlsson <magnus.karlsson@gmail.com>,
	Maryam Tahhan <mtahhan@redhat.com>,
	xdp-hints@xdp-project.net, netdev@vger.kernel.org,
	intel-wired-lan@lists.osuosl.org, linux-kernel@vger.kernel.org
Subject: [xdp-hints] Re: [PATCH RESEND bpf-next 14/15] net, xdp: allow metadata > 32
Date: Mon, 22 May 2023 17:28:15 +0200	[thread overview]
Message-ID: <d53f0150-d74b-7cf6-8fe7-324131b43982@intel.com> (raw)
In-Reply-To: <fed6ef09-0f5b-8c3d-0484-bb0995d09282@redhat.com>

From: Jesper Dangaard Brouer <jbrouer@redhat.com>
Date: Mon, 22 May 2023 13:41:43 +0200

> 
> 
> On 19/05/2023 18.35, Alexander Lobakin wrote:
>> From: Jesper Dangaard Brouer <jbrouer@redhat.com>
>> Date: Tue, 16 May 2023 17:35:27 +0200

[...]

> Not talking about your changes (in this patch).
> 
> I'm realizing that SKBs using metadata area will have a performance hit
> due to accessing another cacheline (the meta_len in skb_shared_info).
> 
> IIRC Daniel complained about this performance hit (in the past), I guess
> this explains it.  IIRC Cilium changed to use percpu variables/datastore
> to workaround this.

Why should we compare metadata of skbs on GRO anyway? I was disabling it
the old hints series (conditionally, if driver asks), moreover...
...if metadata contains full checksum, GRO will be broken completely due
to this comparison (or any other frame-unique fields. VLAN tags and
hashes are okay).

> 
> 
>> The whole xdp_metalen_invalid() gets expanded into:
>>
>>     return (metalen % 4) || metalen > 255;
>>
>> at compile-time. All those typeof shenanigans are only to not open-code
>> meta_len's type/size/max.
>>
>>>
>>> But only use for SKBs that gets created from xdp with metadata, right?
>>>
> 
> Normal netstack processing actually access this skb_shinfo->meta_len in
> gro_list_prepare().  As the caller dev_gro_receive() later access other
> memory in skb_shared_info, then the GRO code path already takes this hit
> to begin with.

You access skb_shinfo() often even before running XDP program, for
example, when a frame is multi-buffer. Plus HW timestamps are also
there, and so on.

> 
> --Jesper
> 

Thanks,
Olek

  reply	other threads:[~2023-05-22 15:30 UTC|newest]

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-05-12 15:25 [xdp-hints] [PATCH RESEND bpf-next 00/15] new kfunc XDP hints and ice implementation Larysa Zaremba
2023-05-12 15:25 ` [xdp-hints] [PATCH RESEND bpf-next 01/15] ice: make RX hash reading code more reusable Larysa Zaremba
2023-05-19 16:46   ` [xdp-hints] " Alexander Lobakin
2023-05-22 15:03     ` Larysa Zaremba
2023-05-22 15:36       ` Alexander Lobakin
2023-05-12 15:25 ` [xdp-hints] [PATCH RESEND bpf-next 02/15] ice: make RX HW timestamp " Larysa Zaremba
2023-05-19 16:52   ` [xdp-hints] " Alexander Lobakin
2023-05-22 15:07     ` Larysa Zaremba
2023-05-12 15:25 ` [xdp-hints] [PATCH RESEND bpf-next 03/15] ice: make RX checksum checking " Larysa Zaremba
2023-05-22 15:51   ` [xdp-hints] " Alexander Lobakin
2023-05-22 16:05     ` Larysa Zaremba
2023-05-12 15:25 ` [xdp-hints] [PATCH RESEND bpf-next 04/15] ice: Make ptype internal to descriptor info processing Larysa Zaremba
2023-05-12 15:25 ` [xdp-hints] [PATCH RESEND bpf-next 05/15] ice: Introduce ice_xdp_buff Larysa Zaremba
2023-05-22 16:46   ` [xdp-hints] " Alexander Lobakin
2023-05-23  8:02     ` Larysa Zaremba
2023-05-25 11:02       ` Alexander Lobakin
2023-05-12 15:25 ` [xdp-hints] [PATCH RESEND bpf-next 06/15] ice: Support HW timestamp hint Larysa Zaremba
2023-05-12 18:19   ` [xdp-hints] " Stanislav Fomichev
2023-05-16 16:17     ` Jesper Dangaard Brouer
2023-05-12 15:25 ` [xdp-hints] [PATCH RESEND bpf-next 07/15] ice: Support RX hash XDP hint Larysa Zaremba
2023-05-12 18:22   ` [xdp-hints] " Stanislav Fomichev
2023-05-15 13:46     ` Larysa Zaremba
2023-05-12 15:26 ` [xdp-hints] [PATCH RESEND bpf-next 08/15] ice: Support XDP hints in AF_XDP ZC mode Larysa Zaremba
2023-05-12 15:26 ` [xdp-hints] [PATCH RESEND bpf-next 09/15] xdp: Add VLAN tag hint Larysa Zaremba
2023-05-12 18:28   ` [xdp-hints] " Stanislav Fomichev
2023-05-15 15:36   ` Jesper Dangaard Brouer
2023-05-15 16:09     ` Larysa Zaremba
2023-05-22  8:37       ` Jesper Dangaard Brouer
2023-05-22 15:48         ` Larysa Zaremba
2023-05-23 10:16           ` Jesper Dangaard Brouer
2023-05-23 17:35             ` Larysa Zaremba
2023-05-12 15:26 ` [xdp-hints] [PATCH RESEND bpf-next 10/15] ice: Implement " Larysa Zaremba
2023-05-12 18:31   ` [xdp-hints] " Stanislav Fomichev
2023-05-15 13:41     ` Larysa Zaremba
2023-05-15 15:07       ` Jesper Dangaard Brouer
2023-05-15 15:45         ` Larysa Zaremba
2023-05-12 15:26 ` [xdp-hints] [PATCH RESEND bpf-next 11/15] xdp: Add checksum level hint Larysa Zaremba
2023-05-12 18:34   ` [xdp-hints] " Stanislav Fomichev
2023-05-15 13:49     ` Larysa Zaremba
2023-05-12 15:26 ` [xdp-hints] [PATCH RESEND bpf-next 12/15] ice: Implement " Larysa Zaremba
2023-05-12 15:26 ` [xdp-hints] [PATCH RESEND bpf-next 13/15] selftests/bpf: Allow VLAN packets in xdp_hw_metadata Larysa Zaremba
2023-05-12 18:33   ` [xdp-hints] " Stanislav Fomichev
2023-05-15 14:05     ` Larysa Zaremba
2023-05-12 15:26 ` [xdp-hints] [PATCH RESEND bpf-next 14/15] net, xdp: allow metadata > 32 Larysa Zaremba
2023-05-15 16:17   ` [xdp-hints] " Jesper Dangaard Brouer
2023-05-15 17:08     ` Larysa Zaremba
2023-05-16 12:37       ` Alexander Lobakin
2023-05-16 15:35         ` Jesper Dangaard Brouer
2023-05-19 16:35           ` Alexander Lobakin
2023-05-22 11:41             ` Jesper Dangaard Brouer
2023-05-22 15:28               ` Alexander Lobakin [this message]
2023-05-22 15:55                 ` Daniel Borkmann
2023-05-12 15:26 ` [xdp-hints] [PATCH RESEND bpf-next 15/15] selftests/bpf: Add flags and new hints to xdp_hw_metadata Larysa Zaremba
2023-05-12 18:37   ` [xdp-hints] " Stanislav Fomichev

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