On Wed, Sep 15, 2010 at 5:19 AM, Guillaume Letellier <guillaume.letell...@arm.com> wrote: > Hi, > >> Also available is an early release of optimised string routines for >> the Cortex-A series, including a mix of NEON and Thumb-2 versions of >> memcpy(), memset(), strcpy(), strcmp(), and strlen(). For more >> information see: >> https://launchpad.net/cortex-strings > > My understanding is that the NEON optimisation will give some performance > gain *ONLY* on Cortex-A8 but it will also burn more energy. On other CPU, > e.g. Cortex-A9, there is no performance gain but still it will cost more > energy.
I've heard that too but never had it confirmed. I will ask. The output of this project will be a set of routines specialised for Thumb-2, NEON, Cortex-A8, and Cortex-A9, where there is a benefit in doing variants for each. We need good non-NEON versions as NEON is optional and it can't be used in the Linux kernel. > Linaro toolchain doesn't target a specific platform but is generic for armv7 > platforms. Are you expecting to see those optimisations turned on in Linaro > toolchain? Sorry, I don't understand the question. We want to spread these routines out and get them integrated into all of the upstream C libraries including NewLib, Bionic, and GLIBC. > The NEON-optimised version is also beneficial for large copies, but it is not > on short copies when the NEON unit has to be powered up (Linux kernel will > get an exception to turn it on). I guess your benchmark didn't take that into > account. Can the NEON-optimised version be changed so that it is not used for > small copies? My understanding is that the NEON unit is on per process, so once you've turned it on once it should stay on. I assume the turn on cost is amortised across a run. Note that if the data is not in the L1 cache then the NEON unit wins even for small-ish (~64 byte) copies. -- Michael _______________________________________________ linaro-toolchain mailing list linaro-toolchain@lists.linaro.org http://lists.linaro.org/mailman/listinfo/linaro-toolchain
