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Message-ID: <20180502170424-mutt-send-email-mst@kernel.org>
Date: Wed, 2 May 2018 17:17:11 +0300
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Vlad Yasevich <vyasevic@...hat.com>
Cc: Vladislav Yasevich <vyasevich@...il.com>, netdev@...r.kernel.org,
linux-sctp@...r.kernel.org,
virtualization@...ts.linux-foundation.org,
virtio-dev@...ts.oasis-open.org, jasowang@...hat.com,
nhorman@...driver.com, marcelo.leitner@...il.com
Subject: Re: [PATCH V2 net-next 5/6] macvlan/macvtap: Add support for SCTP
checksum offload.
On Wed, May 02, 2018 at 10:00:14AM -0400, Vlad Yasevich wrote:
> On 05/02/2018 09:46 AM, Michael S. Tsirkin wrote:
> > On Wed, May 02, 2018 at 09:27:00AM -0400, Vlad Yasevich wrote:
> >> On 05/01/2018 11:24 PM, Michael S. Tsirkin wrote:
> >>> On Tue, May 01, 2018 at 10:07:38PM -0400, Vladislav Yasevich wrote:
> >>>> Since we now have support for software CRC32c offload, turn it on
> >>>> for macvlan and macvtap devices so that guests can take advantage
> >>>> of offload SCTP checksums to the host or host hardware.
> >>>>
> >>>> Signed-off-by: Vladislav Yasevich <vyasevic@...hat.com>
> >>>> ---
> >>>> drivers/net/macvlan.c | 5 +++--
> >>>> drivers/net/tap.c | 8 +++++---
> >>>> 2 files changed, 8 insertions(+), 5 deletions(-)
> >>>>
> >>>> diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c
> >>>> index 725f4b4..646b730 100644
> >>>> --- a/drivers/net/macvlan.c
> >>>> +++ b/drivers/net/macvlan.c
> >>>> @@ -834,7 +834,7 @@ static struct lock_class_key macvlan_netdev_addr_lock_key;
> >>>>
> >>>> #define ALWAYS_ON_OFFLOADS \
> >>>> (NETIF_F_SG | NETIF_F_HW_CSUM | NETIF_F_GSO_SOFTWARE | \
> >>>> - NETIF_F_GSO_ROBUST | NETIF_F_GSO_ENCAP_ALL)
> >>>> + NETIF_F_GSO_ROBUST | NETIF_F_GSO_ENCAP_ALL | NETIF_F_SCTP_CRC)
> >>>>
> >>>> #define ALWAYS_ON_FEATURES (ALWAYS_ON_OFFLOADS | NETIF_F_LLTX)
> >>>>
> >>>> @@ -842,7 +842,8 @@ static struct lock_class_key macvlan_netdev_addr_lock_key;
> >>>> (NETIF_F_SG | NETIF_F_HW_CSUM | NETIF_F_HIGHDMA | NETIF_F_FRAGLIST | \
> >>>> NETIF_F_GSO | NETIF_F_TSO | NETIF_F_LRO | \
> >>>> NETIF_F_TSO_ECN | NETIF_F_TSO6 | NETIF_F_GRO | NETIF_F_RXCSUM | \
> >>>> - NETIF_F_HW_VLAN_CTAG_FILTER | NETIF_F_HW_VLAN_STAG_FILTER)
> >>>> + NETIF_F_HW_VLAN_CTAG_FILTER | NETIF_F_HW_VLAN_STAG_FILTER | \
> >>>> + NETIF_F_SCTP_CRC)
> >>>>
> >>>> #define MACVLAN_STATE_MASK \
> >>>> ((1<<__LINK_STATE_NOCARRIER) | (1<<__LINK_STATE_DORMANT))
> >>>> diff --git a/drivers/net/tap.c b/drivers/net/tap.c
> >>>> index 9b6cb78..2c8512b 100644
> >>>> --- a/drivers/net/tap.c
> >>>> +++ b/drivers/net/tap.c
> >>>> @@ -369,8 +369,7 @@ rx_handler_result_t tap_handle_frame(struct sk_buff **pskb)
> >>>> * check, we either support them all or none.
> >>>> */
> >>>> if (skb->ip_summed == CHECKSUM_PARTIAL &&
> >>>> - !(features & NETIF_F_CSUM_MASK) &&
> >>>> - skb_checksum_help(skb))
> >>>> + skb_csum_hwoffload_help(skb, features))
> >>>> goto drop;
> >>>> if (ptr_ring_produce(&q->ring, skb))
> >>>> goto drop;
> >>>> @@ -945,6 +944,9 @@ static int set_offload(struct tap_queue *q, unsigned long arg)
> >>>> }
> >>>> }
> >>>>
> >>>> + if (arg & TUN_F_SCTP_CSUM)
> >>>> + feature_mask |= NETIF_F_SCTP_CRC;
> >>>> +
> >>>
> >>> so this still affects TX, shouldn't this affect RX instead?
> >>
> >> There is no bit to set on the RX path just like there is no bit to set on the RX patch
> >> for TUN_F_CSUM.
> >>
> >> We only invert TSO offloads, not checksum offloads as the comment below states.
> >> For checksum, macvtap has to compute the checksum itself in tap_handle_frame() above.
> >> It uses tx feature bits to see if needs do to the checksum.
> >>
> >> If you think we need another flag to macvtap to control RXCSUM, that would need to be
> >> separate and cover standard TCP checksum as well.
> >>
> >> -vlad
> >
> > Confused. What is the meaning of TUN_F_SCTP_CSUM? I assume this is
> > a way for userspace to tell tun device: "I can handle
> > packets without SCTP checksum, pls send them my way".
>
> Yes, just as TUN_F_CSUM means that tun device can handle packets with
> partial tcp/udp checksum.
>
> >
> > Now what is the implication for macvtap?
>
> The implication is exactly the same as for TUN_F_CSUM. If the
> flag is set on the macvtap device, the TX checksum feature is
> turned on.
I guess I will have to go back and re-read that code - I do not remember
what does TUN_F_CSUM does by now. Here is a quick question that might
help me:
Let's assume userspace does not set TUN_F_SCTP_CSUM and device
does not calculate the checksums either. I would expect that with
macvtap this then behaves exactly like now with no overhead.
>
> > And why are
> > you setting NETIF_F_SCTP_CRC which is a flag
> > that affects packets sent by guest to host?
>
> Mainly its because we are using just 1 flag to control checksum
> offloading and we need to be able control both tx and rx paths.
Well that's not really the case I think. What we have is controls for tx
offloads for tun. That's TUN_F_CSUM.
there are no rx offloads - userspace can send what it wants.
These are supposed to translate to rx offloads for macvtap.
tx offloads shouldn't be affected at all.
Maybe that's not the case - as I said need to go back and check.
Will try to find the time in the next couple of days.
> What you are suggesting that we either invert what TUN_F_CSUM
> is doing in macvtap case, or have another flag that lets us control
> TX and RX paths separately.
>
> Either case, that would be separate work.
> -vlad
So assuming TUN_F_CSUM affects tx for macvtap do you
agree it's a bug? And should we add to it with
TUN_F_SCTP_CSUM doing the same?
> >
> >
> >>>
> >>>
> >>>> /* tun/tap driver inverts the usage for TSO offloads, where
> >>>> * setting the TSO bit means that the userspace wants to
> >>>> * accept TSO frames and turning it off means that user space
> >>>> @@ -1077,7 +1079,7 @@ static long tap_ioctl(struct file *file, unsigned int cmd,
> >>>> case TUNSETOFFLOAD:
> >>>> /* let the user check for future flags */
> >>>> if (arg & ~(TUN_F_CSUM | TUN_F_TSO4 | TUN_F_TSO6 |
> >>>> - TUN_F_TSO_ECN | TUN_F_UFO))
> >>>> + TUN_F_TSO_ECN | TUN_F_UFO | TUN_F_SCTP_CSUM))
> >>>> return -EINVAL;
> >>>>
> >>>> rtnl_lock();
> >>>> --
> >>>> 2.9.5
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