The existing nohz_full mode does a nice job of suppressing extraneous kernel interrupts for cores that desire it. However, there is a need for a more deterministic mode that rigorously disallows kernel interrupts, even at a higher cost in user/kernel transition time: for example, high-speed networking applications running userspace drivers that will drop packets if they are ever interrupted. These changes attempt to provide an initial draft of such a framework; the changes do not add any overhead to the usual non-nohz_full mode, and only very small overhead to the typical nohz_full mode. A prctl() option (PR_SET_DATAPLANE) is added to control whether processes have requested this stricter semantics, and within that prctl() option we provide a number of different bits for more precise control. Additionally, we add a new command-line boot argument to facilitate debugging where unexpected interrupts are being delivered from. Code that is conceptually similar has been in use in Tilera's Multicore Development Environment since 2008, known as Zero-Overhead Linux, and has seen wide adoption by a range of customers. This patch series represents the first serious attempt to upstream that functionality. Although the current state of the kernel isn't quite ready to run with absolutely no kernel interrupts (for example, workqueues on dataplane cores still remain to be dealt with), this patch series provides a way to make dynamic tradeoffs between avoiding kernel interrupts on the one hand, and making voluntary calls in and out of the kernel more expensive, for tasks that want it. The series (based currently on my arch/tile master tree for 4.2, in turn based on 4.1-rc1) is available at: git://git.kernel.org/pub/scm/linux/kernel/git/cmetcalf/linux-tile.git dataplane Chris Metcalf (6): nohz_full: add support for "dataplane" mode nohz: dataplane: allow tick to be fully disabled for dataplane dataplane nohz: run softirqs synchronously on user entry nohz: support PR_DATAPLANE_QUIESCE nohz: support PR_DATAPLANE_STRICT mode nohz: add dataplane_debug boot flag Documentation/kernel-parameters.txt | 6 ++ arch/tile/mm/homecache.c | 5 +- include/linux/sched.h | 3 + include/linux/tick.h | 12 ++++ include/uapi/linux/prctl.h | 8 +++ kernel/context_tracking.c | 3 + kernel/irq_work.c | 4 +- kernel/sched/core.c | 18 ++++++ kernel/signal.c | 5 ++ kernel/smp.c | 4 ++ kernel/softirq.c | 15 ++++- kernel/sys.c | 8 +++ kernel/time/tick-sched.c | 112 +++++++++++++++++++++++++++++++++++- 13 files changed, 198 insertions(+), 5 deletions(-) -- 2.1.2 -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
