From: Jesper Dangaard Brouer <jbrouer@redhat.com>
To: Alexander Lobakin <alexandr.lobakin@intel.com>,
Jesper Dangaard Brouer <jbrouer@redhat.com>
Cc: brouer@redhat.com, intel-wired-lan@lists.osuosl.org,
"Jesse Brandeburg" <jesse.brandeburg@intel.com>,
"Tony Nguyen" <anthony.l.nguyen@intel.com>,
"David S. Miller" <davem@davemloft.net>,
"Jakub Kicinski" <kuba@kernel.org>,
"Alexei Starovoitov" <ast@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Jesper Dangaard Brouer" <hawk@kernel.org>,
"John Fastabend" <john.fastabend@gmail.com>,
"Björn Töpel" <bjorn@kernel.org>,
"Maciej Fijalkowski" <maciej.fijalkowski@intel.com>,
"Michal Swiatkowski" <michal.swiatkowski@linux.intel.com>,
"Jithu Joseph" <jithu.joseph@intel.com>,
"Martin KaFai Lau" <kafai@fb.com>,
"Song Liu" <songliubraving@fb.com>,
"KP Singh" <kpsingh@kernel.org>, "Yonghong Song" <yhs@fb.com>,
"Andrii Nakryiko" <andrii@kernel.org>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
bpf@vger.kernel.org
Subject: Re: [PATCH v4 net-next 1/9] i40e: don't reserve excessive XDP_PACKET_HEADROOM on XSK Rx to skb
Date: Fri, 10 Dec 2021 14:31:45 +0100 [thread overview]
Message-ID: <ccd27f5f-31c4-603f-ea36-ad32b16325b9@redhat.com> (raw)
In-Reply-To: <20211209173307.5003-1-alexandr.lobakin@intel.com>
On 09/12/2021 18.33, Alexander Lobakin wrote:
> From: Jesper Dangaard Brouer <jbrouer@redhat.com>
> Date: Thu, 9 Dec 2021 09:19:46 +0100
>
>> On 08/12/2021 15.06, Alexander Lobakin wrote:
>>> {__,}napi_alloc_skb() allocates and reserves additional NET_SKB_PAD
>>> + NET_IP_ALIGN for any skb.
>>> OTOH, i40e_construct_skb_zc() currently allocates and reserves
>>> additional `xdp->data - xdp->data_hard_start`, which is
>>> XDP_PACKET_HEADROOM for XSK frames.
>>> There's no need for that at all as the frame is post-XDP and will
>>> go only to the networking stack core.
>>
>> I disagree with this assumption, that headroom is not needed by netstack.
>> Why "no need for that at all" for netstack?
>
> napi_alloc_skb() in our particular case will reserve 64 bytes, it is
> sufficient for {TCP,UDP,SCTP,...}/IPv{4,6} etc.
My bad, I misunderstood you. I now see (looking at code) that (as you
say) 64 bytes of headroom *is* reserved (in bottom of __napi_alloc_skb).
Thus, the SKB *do* have headroom, so this patch should be fine.
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Do watch out that 64 bytes is not always enough. Notice the define
LL_MAX_HEADER and MAX_HEADER in include/linux/netdevice.h (that tries to
determine worst-case header length) which is above 64 bytes. It is also
affected by HyperV and WiFi configs.
next prev parent reply other threads:[~2021-12-10 13:31 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-08 14:06 [PATCH v4 net-next 0/9] net: intel: napi_alloc_skb() vs metadata Alexander Lobakin
2021-12-08 14:06 ` [PATCH v4 net-next 1/9] i40e: don't reserve excessive XDP_PACKET_HEADROOM on XSK Rx to skb Alexander Lobakin
2021-12-09 8:19 ` Jesper Dangaard Brouer
2021-12-09 17:33 ` Alexander Lobakin
2021-12-10 13:31 ` Jesper Dangaard Brouer [this message]
2022-01-29 8:55 ` [Intel-wired-lan] " Bhandare, KiranX
2021-12-08 14:06 ` [PATCH v4 net-next 2/9] i40e: respect metadata " Alexander Lobakin
2021-12-09 8:27 ` Jesper Dangaard Brouer
2021-12-09 17:38 ` Alexander Lobakin
2021-12-09 18:50 ` Nguyen, Anthony L
2021-12-10 11:08 ` Alexander Lobakin
2022-01-10 11:24 ` [Intel-wired-lan] " Bhandare, KiranX
2021-12-08 14:06 ` [PATCH v4 net-next 3/9] ice: respect metadata in legacy-rx/ice_construct_skb() Alexander Lobakin
2022-01-10 10:16 ` [Intel-wired-lan] " Bhandare, KiranX
2021-12-08 14:06 ` [PATCH v4 net-next 4/9] ice: don't reserve excessive XDP_PACKET_HEADROOM on XSK Rx to skb Alexander Lobakin
2022-01-10 10:13 ` [Intel-wired-lan] " Bhandare, KiranX
2021-12-08 14:06 ` [PATCH v4 net-next 5/9] ice: respect metadata " Alexander Lobakin
2022-01-10 11:37 ` [Intel-wired-lan] " Bhandare, KiranX
2021-12-08 14:06 ` [PATCH v4 net-next 6/9] igc: don't reserve excessive XDP_PACKET_HEADROOM " Alexander Lobakin
2021-12-27 20:34 ` [Intel-wired-lan] " Kraus, NechamaX
2021-12-08 14:07 ` [PATCH v4 net-next 7/9] ixgbe: pass bi->xdp to ixgbe_construct_skb_zc() directly Alexander Lobakin
2022-01-11 7:30 ` [Intel-wired-lan] " Penigalapati, Sandeep
2021-12-08 14:07 ` [PATCH v4 net-next 8/9] ixgbe: don't reserve excessive XDP_PACKET_HEADROOM on XSK Rx to skb Alexander Lobakin
2022-01-11 11:51 ` [Intel-wired-lan] " Penigalapati, Sandeep
2021-12-08 14:07 ` [PATCH v4 net-next 9/9] ixgbe: respect metadata " Alexander Lobakin
2022-01-11 11:52 ` [Intel-wired-lan] " Penigalapati, Sandeep
2022-01-10 10:11 ` [Intel-wired-lan] [PATCH v4 net-next 0/9] net: intel: napi_alloc_skb() vs metadata Bhandare, KiranX
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