Re: [PATCH 13/14] net: inline part of skb_csum_hwoffload_help

[Pavel Begunkov]

On 1/12/22 02:41, David Laight wrote:
> From: Pavel Begunkov
> > Sent: 11 January 2022 20:48
> > On 1/11/22 17:25, David Laight wrote:
> > > From: Pavel Begunkov
> > > > Sent: 11 January 2022 16:59
> > > >
> > > > On 1/11/22 09:24, David Laight wrote:
> > > > > From: Pavel Begunkov
> > > > > > Sent: 11 January 2022 01:22
> > > > > >
> > > > > > Inline a HW csum'ed part of skb_csum_hwoffload_help().
> > > > > >
> > > > > > Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
> > > > > > ---
> > > > > >     include/linux/netdevice.h | 16 ++++++++++++++--
> > > > > >     net/core/dev.c            | 13 +++----------
> > > > > >     2 files changed, 17 insertions(+), 12 deletions(-)
> > > > > >
> > > > > > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> > > > > > index 3213c7227b59..fbe6c764ce57 100644
> > > > > > --- a/include/linux/netdevice.h
> > > > > > +++ b/include/linux/netdevice.h
> > > > > > @@ -4596,8 +4596,20 @@ void netdev_rss_key_fill(void *buffer, size_t len);
> > > > > >
> > > > > >     int skb_checksum_help(struct sk_buff *skb);
> > > > > >     int skb_crc32c_csum_help(struct sk_buff *skb);
> > > > > > -int skb_csum_hwoffload_help(struct sk_buff *skb,
> > > > > > -			    const netdev_features_t features);
> > > > > > +int __skb_csum_hwoffload_help(struct sk_buff *skb,
> > > > > > +			      const netdev_features_t features);
> > > > > > +
> > > > > > +static inline int skb_csum_hwoffload_help(struct sk_buff *skb,
> > > > > > +					  const netdev_features_t features)
> > > > > > +{
> > > > > > +	if (unlikely(skb_csum_is_sctp(skb)))
> > > > > > +		return !!(features & NETIF_F_SCTP_CRC) ? 0 :
> > > > >
> > > > > If that !! doing anything? - doesn't look like it.
> > > >
> > > > It doesn't, but left the original style
> > >
> > > It just makes you think it is needed...
> > >
> > > > > > +			skb_crc32c_csum_help(skb);
> > > > > > +
> > > > > > +	if (features & NETIF_F_HW_CSUM)
> > > > > > +		return 0;
> > > > > > +	return __skb_csum_hwoffload_help(skb, features);
> > > > > > +}
> > > > >
> > > > > Maybe you should remove some bloat by moving the sctp code
> > > > > into the called function.
> > > > > This probably needs something like?
> > > > >
> > > > > {
> > > > > 	if (features & NETIF_F_HW_CSUM && !skb_csum_is_sctp(skb))
> > > > > 		return 0;
> > > > > 	return __skb_csum_hw_offload(skb, features);
> > > > > }
> > > >
> > > > I don't like inlining that sctp chunk myself. It seems your way would
> > > > need another skb_csum_is_sctp() in __skb_csum_hw_offload(), if so I
> > > > don't think it's worth it. Would've been great to put the
> > > > NETIF_F_HW_CSUM check first and hide sctp, but don't think it's
> > > > correct. Would be great to hear some ideas.
> > >
> > > Given the definition:
> > >
> > > static inline bool skb_csum_is_sctp(struct sk_buff *skb)
> > > {
> > > 	return skb->csum_not_inet;
> > > }
> > >
> > > I wouldn't worry about doing it twice.
> > >
> > > Also skb_crc32_csum_help() is only called one.
> > > Make it static (so inlined) and pass 'features' into it.
> > >
> > > In reality sctp is such a slow crappy protocol that a few extra
> > > function calls will make diddly-squit difference.
> > > (And yes, we do actually use the sctp stack.)
> >
> > I was more thinking about non-sctp path without NETIF_F_HW_CSUM
>
> In which case you need the body of __skb_csum_hw_offload()
> and end up doing the 'sctp' check once inside it.
> The 'sctp' check is only done twice for sctp.

Ah yes, might be better indeed

--
Pavel Begunkov