On Tue, 2014-05-20 at 14:24 +0300, Igor Royzis wrote: > Fix accessing GSO fragments memory (and a possible corruption therefore) after > reporting completion in a zero copy callback. The previous fix in the commit > 1fd819ec > orphaned frags which eliminates zero copy advantages. The fix makes the > completion > called after all the fragments were processed avoiding unnecessary > orphaning/copying > from userspace. > > The GSO fragments corruption issue was observed in a typical QEMU/KVM VM > setup that > hosts a Windows guest (since QEMU virtio-net Windows driver doesn't support > GRO). > The fix has been verified by running the HCK OffloadLSO test. > > Signed-off-by: Igor Royzis <[email protected]> > Signed-off-by: Anton Nayshtut <[email protected]> > --- > include/linux/skbuff.h | 1 + > net/core/skbuff.c | 18 +++++++++++++----- > 2 files changed, 14 insertions(+), 5 deletions(-) > > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h > index 08074a8..8c49edc 100644 > --- a/include/linux/skbuff.h > +++ b/include/linux/skbuff.h > @@ -287,6 +287,7 @@ struct skb_shared_info { > struct sk_buff *frag_list; > struct skb_shared_hwtstamps hwtstamps; > __be32 ip6_frag_id; > + struct sk_buff *zcopy_src; >
Before your patch : sizeof(struct skb_shared_info)=0x140 offsetof(struct skb_shared_info, frags[1])=0x40 SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) -> 0x140 After your patch : sizeof(struct skb_shared_info)=0x148 offsetof(struct skb_shared_info, frags[1])=0x48 SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) -> 0x180 Thats a serious bump, because it increases all skb truesizes, and typical skb with one fragment will use 2 cache lines instead of one in struct skb_shared_info, so this adds memory pressure in fast path. So while this patch might increase performance for some workloads, it generally decreases performance on many others. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
