On Fri, 2012-11-02 at 14:23 +0000, Christoph Lameter wrote: > On Mon, 29 Oct 2012, Steven Rostedt wrote: > > > A while ago Frederic posted a series of patches to get an idea on > > how to implement nohz cpusets. Where you can add a task to a cpuset > > and mark the set to be 'nohz'. When the task runs on a CPU and is > > the only task scheduled (nr_running == 1), the tick will stop. > > The idea is to give the task the least amount of kernel interference > > as possible. If the task doesn't do any system calls (and possibly > > even if it does), no timer interrupt will bother it. By using > > isocpus and nohz cpuset, a task would be able to achieve true cpu > > isolation. > > I thought isolcpus was on the way out? If there is no timer interrupt then > there will also be no scheduler activity. Why do we need both?
I probably shouldn't have mentioned isolcpus. I was using that as something that is general to get everything off of a cpu (irq affinity for example). > > Also could we have this support without cpusets? There are multiple means > to do system segmentation (f.e. cgroups) and something like hz control is > pretty basic. Control via some cpumask like irq affinities in f.e. > > /sys/devices/system/cpu/nohz > > or a per cpu flag in > > /sys/devices/system/cpu/cpu0/hz > > would be easier and not be tied to something like cpusets. Frederic will have to answer this. I was just starting with his patches. Note, we are holding off this work for now until Frederic's other work is done (the irq_work and printk updates). > > also it would be best to sync this conceptually with the processors > enabled for rcu processing. Processors can be disabled for rcu processing? Or are you talking about Paul's new work of offloading rcu callbacks? > > Maybe have a series of cpumasks in /sys/devices/system/cpu/ ? > > > This has been long asked for by those in the RT community. If a task > > requires uninterruptible CPU time, this would be able to give a task > > that, even without the full PREEMPT-RT patch set. > > Also those interested in low latency are very very interested in this > feature in particular in support without any preempt support on in the > kernel. > Yep understood. We really need to get things rolling. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
