On Sat, Jun 18, 2022 at 04:19:24PM +0100, Al Viro wrote: > On Sat, Jun 18, 2022 at 08:08:08AM -0600, Jens Axboe wrote: > > Using an ITER_UBUF is more efficient than an ITER_IOV, and for the single > > segment case, there's no reason to use an ITER_IOV when an ITER_UBUF will > > do. Experimental data collected shows that ~2/3rds of iovec imports are > > single segments, from applications using readv/writev or recvmsg/sendmsg > > that are iovec based. > > > > Explicitly check for nr_segs == 1 and import those as ubuf rather than > > iovec based iterators. > > Hadn't we'd been through that before? There is infinibarf code that > assumes ITER_IOVEC for what its ->write_iter() gets (and yes, that's > the one that has ->write() with different semantics). > > And I wouldn't bet a dime on all ->sendmsg() and ->recvmsg() being > flavour-agnostic either... Incidentally, what will your patch do to one-segment readv(2) from e.g. /proc/self/status? Or anything else that has no ->read_iter, for that matter...
