On Mon, Oct 27, 2014 at 12:45 PM, Preeti U Murthy <preeti@xxxxxxxxxxxxxxxxxx> wrote: > On 10/17/2014 12:59 AM, kernelfans@xxxxxxxxx wrote: >> (This patch is a place holder.) >> >> If there is only one vcpu thread is ready(the other vcpu thread can >> wait for it to execute), the primary thread can enter tickless mode, > > We do not configure NOHZ_FULL to y by default. Hence no thread would > enter tickless mode. > But NOHZ_FULL can be chosen by user, and we should survive from it :) >> which causes the primary keeps running, so the secondary has no >> opportunity to exit to host, even they have other tsk on them. > > The secondary threads can still get scheduling ticks. The decrementer of > the secondary threads is still active. So as long as secondary threads > are busy, scheduling ticks will fire and try to schedule a new task on them. > No. As my original thought, after enable KVM on core, the HDEC on secondary is disabled, otherwise the host exit will be too frequent. Any suggestion? Thx, Fan > Regards > Preeti U Murthy >> >> Introduce a kthread (anti_tickless) on primary, so when there is only >> one vcpu thread on primary, the secondary can resort to anti_tickless >> to keep the primary out of tickless mode. >> (I thought that anti_tickless thread can goto NAP, so we can let the >> secondary run). >> >> Signed-off-by: Liu Ping Fan <pingfank@xxxxxxxxxxxxxxxxxx> >> --- >> arch/powerpc/kernel/sysfs.c | 4 +++- >> 1 file changed, 3 insertions(+), 1 deletion(-) >> >> diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c >> index a2595dd..f0b110e 100644 >> --- a/arch/powerpc/kernel/sysfs.c >> +++ b/arch/powerpc/kernel/sysfs.c >> @@ -575,9 +575,11 @@ static ssize_t __used store_kvm_enable(struct device *dev, >> if (!test_bit(core, &kvm_on_core)) >> for (thr = 1; thr< threads_per_core; thr++) >> if (cpu_online(thr * threads_per_core + thr)) >> - cpumask_set_cpu(thr * threads_per_core + thr, &stop_cpus); >> + cpumask_set_cpu(core * threads_per_core + thr, &stop_cpus); >> >> stop_machine(xics_migrate_irqs_away_secondary, NULL, &stop_cpus); >> + /* fixme, create a kthread on primary hwthread to handle tickless mode */ >> + //kthread_create_on_cpu(prevent_tickless, NULL, core * threads_per_core, "ppckvm_prevent_tickless"); >> set_bit(core, &kvm_on_core); >> return count; >> } >> > -- To unsubscribe from this list: send the line "unsubscribe kvm-ppc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
