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* xdp generic default option
@ 2020-08-19  9:28 Lorenzo Bianconi
  2020-08-19 14:39 ` Toke Høiland-Jørgensen
                   ` (2 more replies)
  0 siblings, 3 replies; 6+ messages in thread
From: Lorenzo Bianconi @ 2020-08-19  9:28 UTC (permalink / raw)
  To: andriin; +Cc: bpf, netdev, Jesper Dangaard Brouer, David Miller, ast

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Hi Andrii,

working on xdp multi-buff I figured out now xdp generic is the default choice
if not specified by userspace. In particular after commit 7f0a838254bd
("bpf, xdp: Maintain info on attached XDP BPF programs in net_device"), running
the command below, XDP will run in generic mode even if the underlay driver
support XDP in native mode:

$ip link set dev eth0 xdp obj prog.o
$ip link show dev eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdpgeneric qdisc mq state UP mode DEFAULT
   group default qlen 1024
   link/ether f0:ad:4e:09:6b:57 brd ff:ff:ff:ff:ff:ff
   prog/xdp id 1 tag 3b185187f1855c4c jited 

Is it better to use xdpdrv as default choice if not specified by userspace?
doing something like:

diff --git a/net/core/dev.c b/net/core/dev.c
index a00aa737ce29..1f85880ee412 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -8747,9 +8747,9 @@ static enum bpf_xdp_mode dev_xdp_mode(u32 flags)
 {
 	if (flags & XDP_FLAGS_HW_MODE)
 		return XDP_MODE_HW;
-	if (flags & XDP_FLAGS_DRV_MODE)
-		return XDP_MODE_DRV;
-	return XDP_MODE_SKB;
+	if (flags & XDP_FLAGS_SKB_MODE)
+		return XDP_MODE_SKB;
+	return XDP_MODE_DRV;
 }
 
 static bpf_op_t dev_xdp_bpf_op(struct net_device *dev, enum bpf_xdp_mode mode)

Regards,
Lorenzo

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^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: xdp generic default option
  2020-08-19  9:28 xdp generic default option Lorenzo Bianconi
@ 2020-08-19 14:39 ` Toke Høiland-Jørgensen
  2020-08-19 19:07 ` Jakub Kicinski
  2020-08-19 20:57 ` Andrii Nakryiko
  2 siblings, 0 replies; 6+ messages in thread
From: Toke Høiland-Jørgensen @ 2020-08-19 14:39 UTC (permalink / raw)
  To: Lorenzo Bianconi, andriin
  Cc: bpf, netdev, Jesper Dangaard Brouer, David Miller, ast

Lorenzo Bianconi <lorenzo@kernel.org> writes:

> Hi Andrii,
>
> working on xdp multi-buff I figured out now xdp generic is the default choice
> if not specified by userspace. In particular after commit 7f0a838254bd
> ("bpf, xdp: Maintain info on attached XDP BPF programs in net_device"), running
> the command below, XDP will run in generic mode even if the underlay driver
> support XDP in native mode:
>
> $ip link set dev eth0 xdp obj prog.o
> $ip link show dev eth0
> 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdpgeneric qdisc mq state UP mode DEFAULT
>    group default qlen 1024
>    link/ether f0:ad:4e:09:6b:57 brd ff:ff:ff:ff:ff:ff
>    prog/xdp id 1 tag 3b185187f1855c4c jited

Yeah, defaulting to xdpgeneric is not a good idea (and a change in
behaviour; I get native mode on the same command on a 5.8 kernel)...

-Toke


^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: xdp generic default option
  2020-08-19  9:28 xdp generic default option Lorenzo Bianconi
  2020-08-19 14:39 ` Toke Høiland-Jørgensen
@ 2020-08-19 19:07 ` Jakub Kicinski
  2020-08-19 20:57 ` Andrii Nakryiko
  2 siblings, 0 replies; 6+ messages in thread
From: Jakub Kicinski @ 2020-08-19 19:07 UTC (permalink / raw)
  To: Lorenzo Bianconi
  Cc: andriin, bpf, netdev, Jesper Dangaard Brouer, David Miller, ast

On Wed, 19 Aug 2020 11:28:11 +0200 Lorenzo Bianconi wrote:
> Hi Andrii,
> 
> working on xdp multi-buff I figured out now xdp generic is the default choice
> if not specified by userspace. In particular after commit 7f0a838254bd
> ("bpf, xdp: Maintain info on attached XDP BPF programs in net_device"), running
> the command below, XDP will run in generic mode even if the underlay driver
> support XDP in native mode:

Make me wonder if bpf/test_offload.py was ever run on those changes :/

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: xdp generic default option
  2020-08-19  9:28 xdp generic default option Lorenzo Bianconi
  2020-08-19 14:39 ` Toke Høiland-Jørgensen
  2020-08-19 19:07 ` Jakub Kicinski
@ 2020-08-19 20:57 ` Andrii Nakryiko
  2020-08-20  8:25   ` Jesper Dangaard Brouer
  2 siblings, 1 reply; 6+ messages in thread
From: Andrii Nakryiko @ 2020-08-19 20:57 UTC (permalink / raw)
  To: Lorenzo Bianconi
  Cc: Andrii Nakryiko, bpf, Networking, Jesper Dangaard Brouer,
	David Miller, Alexei Starovoitov

On Wed, Aug 19, 2020 at 2:29 AM Lorenzo Bianconi <lorenzo@kernel.org> wrote:
>
> Hi Andrii,
>
> working on xdp multi-buff I figured out now xdp generic is the default choice
> if not specified by userspace. In particular after commit 7f0a838254bd
> ("bpf, xdp: Maintain info on attached XDP BPF programs in net_device"), running
> the command below, XDP will run in generic mode even if the underlay driver
> support XDP in native mode:
>
> $ip link set dev eth0 xdp obj prog.o
> $ip link show dev eth0
> 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdpgeneric qdisc mq state UP mode DEFAULT
>    group default qlen 1024
>    link/ether f0:ad:4e:09:6b:57 brd ff:ff:ff:ff:ff:ff
>    prog/xdp id 1 tag 3b185187f1855c4c jited
>
> Is it better to use xdpdrv as default choice if not specified by userspace?
> doing something like:
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index a00aa737ce29..1f85880ee412 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -8747,9 +8747,9 @@ static enum bpf_xdp_mode dev_xdp_mode(u32 flags)
>  {
>         if (flags & XDP_FLAGS_HW_MODE)
>                 return XDP_MODE_HW;
> -       if (flags & XDP_FLAGS_DRV_MODE)
> -               return XDP_MODE_DRV;
> -       return XDP_MODE_SKB;
> +       if (flags & XDP_FLAGS_SKB_MODE)
> +               return XDP_MODE_SKB;
> +       return XDP_MODE_DRV;
>  }
>

I think the better way would be to choose XDP_MODE_DRV if ndo_bpf !=
NULL and XDP_MODE_SKB otherwise. That seems to be matching original
behavior, no?

It was not my intent to change the behavior, sorry about that. I'll
post patch a bit later today.


>  static bpf_op_t dev_xdp_bpf_op(struct net_device *dev, enum bpf_xdp_mode mode)
>
> Regards,
> Lorenzo

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: xdp generic default option
  2020-08-19 20:57 ` Andrii Nakryiko
@ 2020-08-20  8:25   ` Jesper Dangaard Brouer
  2020-08-20 14:00     ` David Ahern
  0 siblings, 1 reply; 6+ messages in thread
From: Jesper Dangaard Brouer @ 2020-08-20  8:25 UTC (permalink / raw)
  To: Andrii Nakryiko
  Cc: Lorenzo Bianconi, Andrii Nakryiko, bpf, Networking, David Miller,
	Alexei Starovoitov, brouer, David Ahern,
	Toke Høiland-Jørgensen

On Wed, 19 Aug 2020 13:57:51 -0700
Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:

> On Wed, Aug 19, 2020 at 2:29 AM Lorenzo Bianconi <lorenzo@kernel.org> wrote:
> >
> > Hi Andrii,
> >
> > working on xdp multi-buff I figured out now xdp generic is the default choice
> > if not specified by userspace. In particular after commit 7f0a838254bd
> > ("bpf, xdp: Maintain info on attached XDP BPF programs in net_device"), running
> > the command below, XDP will run in generic mode even if the underlay driver
> > support XDP in native mode:
> >
> > $ip link set dev eth0 xdp obj prog.o
> > $ip link show dev eth0
> > 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdpgeneric qdisc mq state UP mode DEFAULT
> >    group default qlen 1024
> >    link/ether f0:ad:4e:09:6b:57 brd ff:ff:ff:ff:ff:ff
> >    prog/xdp id 1 tag 3b185187f1855c4c jited
> >
> > Is it better to use xdpdrv as default choice if not specified by userspace?
> > doing something like:
> >
> > diff --git a/net/core/dev.c b/net/core/dev.c
> > index a00aa737ce29..1f85880ee412 100644
> > --- a/net/core/dev.c
> > +++ b/net/core/dev.c
> > @@ -8747,9 +8747,9 @@ static enum bpf_xdp_mode dev_xdp_mode(u32 flags)
> >  {
> >         if (flags & XDP_FLAGS_HW_MODE)
> >                 return XDP_MODE_HW;
> > -       if (flags & XDP_FLAGS_DRV_MODE)
> > -               return XDP_MODE_DRV;
> > -       return XDP_MODE_SKB;
> > +       if (flags & XDP_FLAGS_SKB_MODE)
> > +               return XDP_MODE_SKB;
> > +       return XDP_MODE_DRV;
> >  }
> >  
> 
> I think the better way would be to choose XDP_MODE_DRV if ndo_bpf !=
> NULL and XDP_MODE_SKB otherwise. That seems to be matching original
> behavior, no?

Yes, but this silent fallback to XDP_MODE_SKB (generic-XDP) have
cause a lot of support issues in the past.  I wish we could change it.
We already changed all the samples/bpf/ to ask for XDP_FLAGS_DRV_MODE,
so they behave this way.

d50ecc46d18f ("samples/bpf: Attach XDP programs in driver mode by default")
 https://git.kernel.org/torvalds/c/d50ecc46d18fa

> It was not my intent to change the behavior, sorry about that. I'll
> post patch a bit later today.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer


^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: xdp generic default option
  2020-08-20  8:25   ` Jesper Dangaard Brouer
@ 2020-08-20 14:00     ` David Ahern
  0 siblings, 0 replies; 6+ messages in thread
From: David Ahern @ 2020-08-20 14:00 UTC (permalink / raw)
  To: Jesper Dangaard Brouer, Andrii Nakryiko
  Cc: Lorenzo Bianconi, Andrii Nakryiko, bpf, Networking, David Miller,
	Alexei Starovoitov, Toke Høiland-Jørgensen

On 8/20/20 2:25 AM, Jesper Dangaard Brouer wrote:
>>> diff --git a/net/core/dev.c b/net/core/dev.c
>>> index a00aa737ce29..1f85880ee412 100644
>>> --- a/net/core/dev.c
>>> +++ b/net/core/dev.c
>>> @@ -8747,9 +8747,9 @@ static enum bpf_xdp_mode dev_xdp_mode(u32 flags)
>>>  {
>>>         if (flags & XDP_FLAGS_HW_MODE)
>>>                 return XDP_MODE_HW;
>>> -       if (flags & XDP_FLAGS_DRV_MODE)
>>> -               return XDP_MODE_DRV;
>>> -       return XDP_MODE_SKB;
>>> +       if (flags & XDP_FLAGS_SKB_MODE)
>>> +               return XDP_MODE_SKB;
>>> +       return XDP_MODE_DRV;
>>>  }
>>>  
>>
>> I think the better way would be to choose XDP_MODE_DRV if ndo_bpf !=
>> NULL and XDP_MODE_SKB otherwise. That seems to be matching original
>> behavior, no?
> 
> Yes, but this silent fallback to XDP_MODE_SKB (generic-XDP) have
> cause a lot of support issues in the past.  I wish we could change it.
> We already changed all the samples/bpf/ to ask for XDP_FLAGS_DRV_MODE,
> so they behave this way.
> 

I would prefer the flags check in Lorenzo's proposed patch which is an
explicit opt in to the SKB mode.

^ permalink raw reply	[flat|nested] 6+ messages in thread

end of thread, other threads:[~2020-08-20 14:06 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-08-19  9:28 xdp generic default option Lorenzo Bianconi
2020-08-19 14:39 ` Toke Høiland-Jørgensen
2020-08-19 19:07 ` Jakub Kicinski
2020-08-19 20:57 ` Andrii Nakryiko
2020-08-20  8:25   ` Jesper Dangaard Brouer
2020-08-20 14:00     ` David Ahern

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