On Fri, Dec 08, 2017 at 10:37:34AM -0500, Neil Horman wrote: > 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.
Hmmm, maybe, yes. It would be like sctp_stream_interleave[asoc->stream.si].make_datafrag(...) Then same goes for pf->af, probably. > > 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. Yep, that was my 2nd paragraph above :-) but it only works for cases such as this one. Marcelo > > Neil > > > Marcelo > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-sctp" in > > the body of a message to majord...@vger.kernel.org > > 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 majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >
