On 06/01/2012 06:29 PM, Jan Beulich wrote: >>>> On 01.06.12 at 11:11, "Srivatsa S. Bhat" <[email protected]> > wrote: >> xen_play_dead calls cpu_bringup() which looks weird, because xen_play_dead() >> is invoked in the cpu down path, whereas cpu_bringup() (as the name >> suggests) is useful in the cpu bringup path. > > This might not be correct - the code as it is without this change is > safe even when the vCPU gets onlined back later by an external > entity (e.g. the Xen tool stack), and it would in that case resume > at the return point of the VCPUOP_down hypercall. That might > be a heritage from the original XenoLinux tree though, and be > meaningless in pv-ops context - Jeremy, Konrad? > > Possibly it was bogus/unused even in that original tree - Keir? >
Thanks for your comments Jan! In case this change is wrong, the other method I had in mind was to call cpu_bringup_and_idle() in xen_play_dead(). (Even ARM does something similar, in the sense that it runs the cpu bringup code including cpu_idle(), in the cpu offline path, namely the cpu_die() function). Would that approach work for xen as well? If yes, then we wouldn't have any issues to convert xen to generic code. Regards, Srivatsa S. Bhat > >> Getting rid of xen_play_dead()'s dependency on cpu_bringup() helps in >> hooking on to the generic SMP booting framework. >> >> Also remove the extra call to preempt_enable() added by commit 41bd956 >> (xen/smp: Fix CPU online/offline bug triggering a BUG: scheduling while >> atomic) because it becomes unnecessary after this change. >> >> Cc: Konrad Rzeszutek Wilk <[email protected]> >> Cc: Jeremy Fitzhardinge <[email protected]> >> Cc: Thomas Gleixner <[email protected]> >> Cc: Ingo Molnar <[email protected]> >> Cc: "H. Peter Anvin" <[email protected]> >> Cc: [email protected] >> Cc: [email protected] >> Cc: [email protected] >> Signed-off-by: Srivatsa S. Bhat <[email protected]> >> --- >> >> arch/x86/xen/smp.c | 8 -------- >> 1 files changed, 0 insertions(+), 8 deletions(-) >> >> diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c >> index 09a7199..602d6b7 100644 >> --- a/arch/x86/xen/smp.c >> +++ b/arch/x86/xen/smp.c >> @@ -417,14 +417,6 @@ static void __cpuinit xen_play_dead(void) /* used only >> with HOTPLUG_CPU */ >> { >> play_dead_common(); >> HYPERVISOR_vcpu_op(VCPUOP_down, smp_processor_id(), NULL); >> - cpu_bringup(); >> - /* >> - * Balance out the preempt calls - as we are running in cpu_idle >> - * loop which has been called at bootup from cpu_bringup_and_idle. >> - * The cpucpu_bringup_and_idle called cpu_bringup which made a >> - * preempt_disable() So this preempt_enable will balance it out. >> - */ >> - preempt_enable(); >> } >> >> #else /* !CONFIG_HOTPLUG_CPU */ >> >> _______________________________________________ Virtualization mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/virtualization
