linux-kernel - Re: [Xen-devel] [PATCH v6 10/11] x86, xen: support vcpu preempted check

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Date:   Fri, 28 Oct 2016 15:43:25 -0400
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        virtualization@...ts.linux-foundation.org,
        linux-s390@...r.kernel.org, xen-devel-request@...ts.xenproject.org,
        kvm@...r.kernel.org, xen-devel@...ts.xenproject.org,
        x86@...nel.org, kernellwp@...il.com, jgross@...e.com,
        David.Laight@...LAB.COM, rkrcmar@...hat.com, peterz@...radead.org,
        benh@...nel.crashing.org, bsingharora@...il.com,
        will.deacon@....com, borntraeger@...ibm.com, mingo@...hat.com,
        paulus@...ba.org, mpe@...erman.id.au, pbonzini@...hat.com,
        paulmck@...ux.vnet.ibm.com, boqun.feng@...il.com
Subject: Re: [Xen-devel] [PATCH v6 10/11] x86, xen: support vcpu preempted
 check

On Fri, Oct 28, 2016 at 04:11:26AM -0400, Pan Xinhui wrote:
> From: Juergen Gross <jgross@...e.com>
> 
> Support the vcpu_is_preempted() functionality under Xen. This will
> enhance lock performance on overcommitted hosts (more runnable vcpus
> than physical cpus in the system) as doing busy waits for preempted
> vcpus will hurt system performance far worse than early yielding.
> 
> A quick test (4 vcpus on 1 physical cpu doing a parallel build job
> with "make -j 8") reduced system time by about 5% with this patch.
> 
> Signed-off-by: Juergen Gross <jgross@...e.com>
> Signed-off-by: Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
> ---
>  arch/x86/xen/spinlock.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
> index 3d6e006..74756bb 100644
> --- a/arch/x86/xen/spinlock.c
> +++ b/arch/x86/xen/spinlock.c
> @@ -114,7 +114,6 @@ void xen_uninit_lock_cpu(int cpu)
>  	per_cpu(irq_name, cpu) = NULL;
>  }
>  
> -

Spurious change.
>  /*
>   * Our init of PV spinlocks is split in two init functions due to us
>   * using paravirt patching and jump labels patching and having to do
> @@ -137,6 +136,8 @@ void __init xen_init_spinlocks(void)
>  	pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock);
>  	pv_lock_ops.wait = xen_qlock_wait;
>  	pv_lock_ops.kick = xen_qlock_kick;
> +
> +	pv_lock_ops.vcpu_is_preempted = xen_vcpu_stolen;
>  }
>  
>  /*
> -- 
> 2.4.11
> 
> 
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