On Fri, Dec 08, 2017 at 12:56:30PM -0200, Marcelo Ricardo Leitner wrote: > On Fri, Dec 08, 2017 at 02:06:04PM +0000, David Laight wrote: > > From: Xin Long > > > Sent: 08 December 2017 13:04 > > ... > > > @@ -264,8 +264,8 @@ struct sctp_datamsg *sctp_datamsg_from_user(struct sctp_association *asoc, > > > frag |= SCTP_DATA_SACK_IMM; > > > } > > > > > > - chunk = sctp_make_datafrag_empty(asoc, sinfo, len, frag, > > > - 0, GFP_KERNEL); > > > + chunk = asoc->stream.si->make_datafrag(asoc, sinfo, len, frag, > > > + GFP_KERNEL); > > > > I know that none of the sctp code is very optimised, but that indirect > > call is going to be horrid. > > Yeah.. but there is no way to avoid the double derreference > considering we only have the asoc pointer in there and we have to > reach the contents of the data chunk operations struct, and the .si > part is the same as 'stream' part as it's a constant offset. > > Due to the for() in there, we could add a variable to store > asoc->stream.si outside the for and then we can do only a single deref > inside it. Xin, can you please try and see if the generated code is > different? > > Other suggestions? > Is it worth replacing the si struct with an index/enum value, and indexing an array of method pointer structs? That would save you at least one dereference. Alternatively you could preform the dereference in two steps (i.e. declare an si pointer on the stack and set it equal to asoc->stream.si, then deref si->make_datafrag at call time. That will at least give the compiler an opportunity to preload the first pointer. Neil > Marcelo > -- > To unsubscribe from this list: send the line "unsubscribe linux-sctp" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-sctp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
