[prev in list] [next in list] [prev in thread] [next in thread] 

List:       linux-parisc
Subject:    Re: [patch 16/37] x86/xen/smp_pv: Remove wait for CPU online
From:       Boris Ostrovsky <boris.ostrovsky () oracle ! com>
Date:       2023-04-17 20:46:17
Message-ID: 9914d517-cf10-a06b-c782-c74d2f24ad46 () oracle ! com
[Download RAW message or body]



On 4/14/23 7:44 PM, Thomas Gleixner wrote:
> Now that the core code drops sparse_irq_lock after the idle thread
> synchronized, it's pointless to wait for the AP to mark itself online.
> 
> Whether the control CPU runs in a wait loop or sleeps in the core code
> waiting for the online operation to complete makes no difference.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: Juergen Gross <jgross@suse.com>
> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Cc: xen-devel@lists.xenproject.org
> ---
> arch/x86/xen/smp_pv.c |   10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
> 
> --- a/arch/x86/xen/smp_pv.c
> +++ b/arch/x86/xen/smp_pv.c
> @@ -340,11 +340,11 @@ static int xen_pv_cpu_up(unsigned int cp
> 
> 	xen_pmu_init(cpu);
> 
> -	rc = HYPERVISOR_vcpu_op(VCPUOP_up, xen_vcpu_nr(cpu), NULL);
> -	BUG_ON(rc);
> -
> -	while (cpu_report_state(cpu) != CPU_ONLINE)
> -		HYPERVISOR_sched_op(SCHEDOP_yield, NULL);
> +	/*
> +	 * Why is this a BUG? If the hypercall fails then everything can be
> +	 * rolled back, no?
> +	 */


In many cases this indicates either some sort of hypervisor internal error or broken \
logic in the guest, so it is, well, a bug. But I suppose it may also be some \
transient condition in the hypervisor (I don't see it now but it can happen in the \
future) so perhaps we should indeed try not to die on the spot.



-boris


> +	BUG_ON(HYPERVISOR_vcpu_op(VCPUOP_up, xen_vcpu_nr(cpu), NULL));
> 
> 	return 0;
> }
> 


[prev in list] [next in list] [prev in thread] [next in thread]