From: Jesper Dangaard Brouer <brouer@redhat.com>
To: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Cc: Saeed Mahameed <saeed@kernel.org>,
Maciej Fijalkowski <maciej.fijalkowski@intel.com>,
Alexander Duyck <alexander.duyck@gmail.com>,
Lorenzo Bianconi <lorenzo@kernel.org>, bpf <bpf@vger.kernel.org>,
Netdev <netdev@vger.kernel.org>,
David Miller <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
shayagr@amazon.com, "Jubran, Samih" <sameehj@amazon.com>,
John Fastabend <john.fastabend@gmail.com>,
dsahern@kernel.org, Eelco Chaudron <echaudro@redhat.com>,
Jason Wang <jasowang@redhat.com>,
brouer@redhat.com
Subject: Re: [PATCH v5 bpf-next 02/14] xdp: initialize xdp_buff mb bit to 0 in all XDP drivers
Date: Tue, 8 Dec 2020 14:29:10 +0100 [thread overview]
Message-ID: <20201208142910.34b7c7e5@carbon> (raw)
In-Reply-To: <20201208103103.GB36228@lore-desk>
On Tue, 8 Dec 2020 11:31:03 +0100
Lorenzo Bianconi <lorenzo.bianconi@redhat.com> wrote:
> > On Mon, 2020-12-07 at 22:37 +0100, Maciej Fijalkowski wrote:
> > > On Mon, Dec 07, 2020 at 01:15:00PM -0800, Alexander Duyck wrote:
> > > > On Mon, Dec 7, 2020 at 8:36 AM Lorenzo Bianconi <lorenzo@kernel.org
> > > > > wrote:
> > > > > Initialize multi-buffer bit (mb) to 0 in all XDP-capable drivers.
> > > > > This is a preliminary patch to enable xdp multi-buffer support.
> > > > >
> > > > > Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
> > > >
> > > > I'm really not a fan of this design. Having to update every driver in
> > > > order to initialize a field that was fragmented is a pain. At a
> > > > minimum it seems like it might be time to consider introducing some
> > > > sort of initializer function for this so that you can update things in
> > > > one central place the next time you have to add a new field instead of
> > > > having to update every individual driver that supports XDP. Otherwise
> > > > this isn't going to scale going forward.
+1
> > > Also, a good example of why this might be bothering for us is a fact that
> > > in the meantime the dpaa driver got XDP support and this patch hasn't been
> > > updated to include mb setting in that driver.
> > >
> > something like
> > init_xdp_buff(hard_start, headroom, len, frame_sz, rxq);
> >
> > would work for most of the drivers.
> >
>
> ack, agree. I will add init_xdp_buff() in v6.
I do like the idea of an initialize helper function.
Remember this is fast-path code and likely need to be inlined.
Further more, remember that drivers can and do optimize the number of
writes they do to xdp_buff. There are a number of fields in xdp_buff
that only need to be initialized once per NAPI. E.g. rxq and frame_sz
(some driver do change frame_sz per packet). Thus, you likely need two
inlined helpers for init.
Again, remember that C-compiler will generate an expensive operation
(rep stos) for clearing a struct if it is initialized like this, where
all member are not initialized (do NOT do this):
struct xdp_buff xdp = {
.rxq = rxq,
.frame_sz = PAGE_SIZE,
};
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
next prev parent reply other threads:[~2020-12-08 13:31 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-07 16:32 [PATCH v5 bpf-next 00/14] mvneta: introduce XDP multi-buffer support Lorenzo Bianconi
2020-12-07 16:32 ` [PATCH v5 bpf-next 01/14] xdp: introduce mb in xdp_buff/xdp_frame Lorenzo Bianconi
2020-12-07 21:16 ` Alexander Duyck
2020-12-07 23:03 ` Saeed Mahameed
2020-12-08 3:16 ` Alexander Duyck
2020-12-08 6:49 ` Saeed Mahameed
2020-12-08 9:47 ` Jesper Dangaard Brouer
2020-12-07 16:32 ` [PATCH v5 bpf-next 02/14] xdp: initialize xdp_buff mb bit to 0 in all XDP drivers Lorenzo Bianconi
2020-12-07 21:15 ` Alexander Duyck
2020-12-07 21:37 ` Maciej Fijalkowski
2020-12-07 23:20 ` Saeed Mahameed
2020-12-08 10:31 ` Lorenzo Bianconi
2020-12-08 13:29 ` Jesper Dangaard Brouer [this message]
2020-12-07 16:32 ` [PATCH v5 bpf-next 03/14] xdp: add xdp_shared_info data structure Lorenzo Bianconi
2020-12-08 0:22 ` Saeed Mahameed
2020-12-08 11:01 ` Lorenzo Bianconi
2020-12-19 14:53 ` Shay Agroskin
2020-12-19 15:30 ` Jamal Hadi Salim
2020-12-21 9:01 ` Jesper Dangaard Brouer
2020-12-21 13:00 ` Jamal Hadi Salim
2020-12-20 17:52 ` Lorenzo Bianconi
2020-12-21 20:55 ` Shay Agroskin
2020-12-07 16:32 ` [PATCH v5 bpf-next 04/14] net: mvneta: update mb bit before passing the xdp buffer to eBPF layer Lorenzo Bianconi
2020-12-07 16:32 ` [PATCH v5 bpf-next 05/14] xdp: add multi-buff support to xdp_return_{buff/frame} Lorenzo Bianconi
2020-12-07 16:32 ` [PATCH v5 bpf-next 06/14] net: mvneta: add multi buffer support to XDP_TX Lorenzo Bianconi
2020-12-19 15:56 ` Shay Agroskin
2020-12-20 18:06 ` Lorenzo Bianconi
2020-12-07 16:32 ` [PATCH v5 bpf-next 07/14] bpf: move user_size out of bpf_test_init Lorenzo Bianconi
2020-12-07 16:32 ` [PATCH v5 bpf-next 08/14] bpf: introduce multibuff support to bpf_prog_test_run_xdp() Lorenzo Bianconi
2020-12-07 16:32 ` [PATCH v5 bpf-next 09/14] bpf: test_run: add xdp_shared_info pointer in bpf_test_finish signature Lorenzo Bianconi
2020-12-07 16:32 ` [PATCH v5 bpf-next 10/14] net: mvneta: enable jumbo frames for XDP Lorenzo Bianconi
2020-12-07 16:32 ` [PATCH v5 bpf-next 11/14] bpf: cpumap: introduce xdp multi-buff support Lorenzo Bianconi
2020-12-19 17:46 ` Shay Agroskin
2020-12-20 17:56 ` Lorenzo Bianconi
2020-12-07 16:32 ` [PATCH v5 bpf-next 12/14] bpf: add multi-buff support to the bpf_xdp_adjust_tail() API Lorenzo Bianconi
2020-12-07 16:32 ` [PATCH v5 bpf-next 13/14] bpf: add new frame_length field to the XDP ctx Lorenzo Bianconi
2020-12-08 22:17 ` Maciej Fijalkowski
2020-12-09 10:35 ` Eelco Chaudron
2020-12-09 11:10 ` Maciej Fijalkowski
2020-12-09 12:07 ` Eelco Chaudron
2020-12-15 13:28 ` Eelco Chaudron
2020-12-15 18:06 ` Maciej Fijalkowski
2020-12-16 14:08 ` Eelco Chaudron
2021-01-15 16:36 ` Eelco Chaudron
2021-01-18 16:48 ` Maciej Fijalkowski
2021-01-20 13:20 ` Eelco Chaudron
2021-02-01 16:00 ` Eelco Chaudron
2020-12-07 16:32 ` [PATCH v5 bpf-next 14/14] bpf: update xdp_adjust_tail selftest to include multi-buffer Lorenzo Bianconi
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