On Mon, Oct 12, 2015 at 08:32:02AM -0700, Paul E. McKenney wrote: > On Mon, Oct 12, 2015 at 05:21:23PM +0200, Frederic Weisbecker wrote: > > This reverts commit 8cb9764fc88b41db11f251e8b2a0d006578b7eb4. > > > > We assumed that nohz full users always want scheduler isolation on full > > dynticks CPUs, therefore we included nohz full CPUs on cpu_isolated_map. > > This means that tasks run by default on CPUs outside the nohz_full range > > unless their affinity is explicity overwritten. > > > > This suits pure isolation workloads but when the machine is needed to > > run common workloads, the available sets of CPUs to run common tasks > > becomes reduced. > > > > We reach an extreme case when CONFIG_NO_HZ_FULL_ALL is enabled as it > > leaves only CPU 0 for non-isolation tasks, which makes people think that > > their supercomputer regressed to 90's UP. > > > > Some nohz full users appear to be interested in running normal workloads > > either before or after an isolation workload. Nohz full isn't optimized > > toward normal workloads but it's still better than UP performance. > > > > We are reaching a limitation in kernel presets here. Lets revert this > > cpu_isolated_map inclusion and let userspace do its own scheduler > > isolation using cpusets or explicit affinity settings. > > > > Reported-by: Ingo Molnar <[email protected]> > > Reported-by: Mike Galbraith <[email protected]> > > Cc: Chris Metcalf <[email protected]> > > Cc: Rik van Riel <[email protected]> > > Cc: Christoph Lameter <[email protected]> > > Cc: Mike Galbraith <[email protected]> > > Cc: Peter Zijlstra <[email protected]> > > Cc: Dave Jones <[email protected]> > > Cc: Oleg Nesterov <[email protected]> > > Cc: Paul E. McKenney <[email protected]> > > Cc: Thomas Gleixner <[email protected]> > > Cc: Ingo Molnar <[email protected]> > > Cc: Alexey Dobriyan <[email protected]> > > Cc: Andrew Morton <[email protected]> > > Signed-off-by: Frederic Weisbecker <[email protected]> > > --- > > kernel/sched/core.c | 3 --- > > 1 file changed, 3 deletions(-) > > > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > > index 6159531..3c35b5f 100644 > > --- a/kernel/sched/core.c > > +++ b/kernel/sched/core.c > > @@ -7238,9 +7238,6 @@ void __init sched_init_smp(void) > > alloc_cpumask_var(&non_isolated_cpus, GFP_KERNEL); > > alloc_cpumask_var(&fallback_doms, GFP_KERNEL); > > > > - /* nohz_full won't take effect without isolating the cpus. */ > > - tick_nohz_full_add_cpus_to(cpu_isolated_map); > > - > > Why not make this controlled by a boot parameter? That preserves > the ease of use for those needing it, but avoids problems from people > doing "make randconfig".
Well it is already. As you pass nohz_full=1-32, you can pass as well isolcpus=1-32 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
