On Tue, Nov 23, 2010 at 11:05:46AM +0100, Brice Goglin wrote: > Le 23/11/2010 10:25, Christopher Yeoh a écrit : > > On Mon, 22 Nov 2010 13:05:27 -0800 > > Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > > >> We have a bit of a track record of adding cool-looking syscalls and > >> then regretting it a few years later. Few people use them, and maybe > >> they weren't so cool after all, and we have to maintain them for > >> ever. Bugs (sometimes security-relevant ones) remain undiscovered for > >> long periods because few people use (or care about) the code. > >> > >> So I think the bar is a high one - higher than it used to be. > >> Convince us that this feature is so important that it's worth all > >> that overhead and risk? > >> > > Well there are the benchmark results to show that there is > > real improvement for MPI implementations (well at least for those > > benchmarks ;-) There's also been a few papers written on something > > quite similar (KNEM) which goes into more detail on the potential gains. > > > > http://runtime.bordeaux.inria.fr/knem/ > > > > I've also heard privately that something very similar has been used in > > at least one device driver to support intranode operations for quite a > > while > > > > Many HPC hardware vendors implemented something like this in their > custom drivers to avoid going through their network loopback for local > communication. Even if their loopback is very fast, going to the NIC and > back to same host isn't really optimal. And I think all of them kept the > traditional approach (double-copy across a shared-memory buffer) for > small messages and only switched to this single-copy model for large > messages (tens or hundreds of kB). CMA and KNEM are "standardizing" all > this work and making it portable across multiple HPC platform/networks. SGI used this concept even for single-byte messages both within the same and across hosts. Thanks, Robin -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>