On Mon, Oct 29, 2012 at 10:27 PM, Steven Rostedt <rost...@goodmis.org> wrote: > > A while ago Frederic posted a series of patches to get an idea on > how to implement nohz cpusets. <snip> > By using > isocpus and nohz cpuset, a task would be able to achieve true cpu > isolation. > > 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. > > This patch set is not for inclusion. It is just to get the topic > at the forefront again. The design requires more work and more > discussion. >
Three additional data points that might be of interest to the discussion: 1. AFAIK both Tilera and Cavium carry patch sets with similar functionality in their respective kernels, so the idea has some real world users already. 2. I tested a previous version of the same patch set (based on 3.3) together with some fixes* and got the same latency, in cycles, from a simple test program and a version of said program running bare metal with no OS. The same program running without this patch got 3 orders of magnitude higher latency. So, this certainly shows some great potential. 3. Even if you don't care about latency at all, on a massively multi-core (or hyperscale, as I've read some people call it now) systems, assigning a task to a single CPU can makes a lot of sense from a cache utilization perspective etc; if you that, this feature can give a performance boost to anything that is mostly CPU bound and perhaps for some workloads that are not so CPU bound as well. Specifically, many high performance computing type of workloads come to mind. So, this has the potential to be useful to both RT folks and HPC folks, I think. [*] A newer version patch set: http://www.spinics.net/lists/linux-mm/msg33860.html and disabling the part that sends IPI to update cputime for nohz/cpuset CPUs. Thanks, Gilad -- Gilad Ben-Yossef Chief Coffee Drinker gi...@benyossef.com Israel Cell: +972-52-8260388 US Cell: +1-973-8260388 http://benyossef.com "If you take a class in large-scale robotics, can you end up in a situation where the homework eats your dog?" -- Jean-Baptiste Queru -- 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/
