On Tue, Oct 10, 2017 at 07:38:38PM +0100, Dave P Martin wrote: > Because of the effect of SVE on the size of the signal frame, the > default vector length used for new processes involves a tradeoff > between performance of SVE-enabled software on the one hand, and > reliability of non-SVE-aware software on the other hand. > > For this reason, the best choice depends on the repertoire of > userspace software in use and is thus best left up to distro > maintainers, sysadmins and developers. > > If CONFIG_SYSCTL is enabled, this patch exposes the default vector > length in /proc/sys/abi/sve_default_vector_length, where boot > scripts or the adventurous can poke it. > > In common with other arm64 ABI sysctls, this control is currently > global: setting it requires CAP_SYS_ADMIN in the root user > namespace, but the value set is effective for subsequent execs in > all namespaces. The control only affects _new_ processes, however: > changing it does not affect the vector length of any existing > process. > > The intended usage model is that if userspace is known to be fully > SVE-tolerant (or a developer is curious to find out) then init > scripts can crank this up during startup. > > Signed-off-by: Dave Martin <Dave.Martin@xxxxxxx> > Reviewed-by: Alex Bennée <alex.bennee@xxxxxxxxxx> Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx> _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
