Re: [PATCH v5 02/12] x86/paravirt: switch time pvops functions to use static_call()

From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
To: Juergen Gross <jgross@suse.com>,
	xen-devel@lists.xenproject.org, x86@kernel.org,
	virtualization@lists.linux-foundation.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-hyperv@vger.kernel.org,
	kvm@vger.kernel.org
Cc: Deep Shah <sdeep@vmware.com>,
	"VMware, Inc." <pv-drivers@vmware.com>,
	Russell King <linux@armlinux.org.uk>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"K. Y. Srinivasan" <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	Wei Liu <wei.liu@kernel.org>, Paolo Bonzini <pbonzini@redhat.com>,
	Sean Christopherson <seanjc@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	Stefano Stabellini <sstabellini@kernel.org>
Subject: Re: [PATCH v5 02/12] x86/paravirt: switch time pvops functions to use static_call()
Date: Mon, 8 Mar 2021 12:00:23 -0500	[thread overview]
Message-ID: <1346dbb1-c43e-9ac2-10e4-3c10cb2ead78@oracle.com> (raw)
In-Reply-To: <20210308122844.30488-3-jgross@suse.com>

On 3/8/21 7:28 AM, Juergen Gross wrote:
> --- a/arch/x86/xen/time.c
> +++ b/arch/x86/xen/time.c
> @@ -379,11 +379,6 @@ void xen_timer_resume(void)
>  	}
>  }
>  
> -static const struct pv_time_ops xen_time_ops __initconst = {
> -	.sched_clock = xen_sched_clock,
> -	.steal_clock = xen_steal_clock,
> -};
> -
>  static struct pvclock_vsyscall_time_info *xen_clock __read_mostly;
>  static u64 xen_clock_value_saved;
>  
> @@ -528,7 +523,8 @@ static void __init xen_time_init(void)
>  void __init xen_init_time_ops(void)
>  {
>  	xen_sched_clock_offset = xen_clocksource_read();
> -	pv_ops.time = xen_time_ops;
> +	static_call_update(pv_steal_clock, xen_steal_clock);
> +	paravirt_set_sched_clock(xen_sched_clock);
>  
>  	x86_init.timers.timer_init = xen_time_init;
>  	x86_init.timers.setup_percpu_clockev = x86_init_noop;
> @@ -570,7 +566,8 @@ void __init xen_hvm_init_time_ops(void)
>  	}
>  
>  	xen_sched_clock_offset = xen_clocksource_read();
> -	pv_ops.time = xen_time_ops;
> +	static_call_update(pv_steal_clock, xen_steal_clock);
> +	paravirt_set_sched_clock(xen_sched_clock);
>  	x86_init.timers.setup_percpu_clockev = xen_time_init;
>  	x86_cpuinit.setup_percpu_clockev = xen_hvm_setup_cpu_clockevents;

There is a bunch of stuff that's common between the two cases so it can be factored out.

>  
> diff --git a/drivers/xen/time.c b/drivers/xen/time.c
> index 108edbcbc040..152dd33bb223 100644
> --- a/drivers/xen/time.c
> +++ b/drivers/xen/time.c
> @@ -7,6 +7,7 @@
>  #include <linux/math64.h>
>  #include <linux/gfp.h>
>  #include <linux/slab.h>
> +#include <linux/static_call.h>
>  
>  #include <asm/paravirt.h>
>  #include <asm/xen/hypervisor.h>
> @@ -175,7 +176,7 @@ void __init xen_time_setup_guest(void)
>  	xen_runstate_remote = !HYPERVISOR_vm_assist(VMASST_CMD_enable,
>  					VMASST_TYPE_runstate_update_flag);
>  
> -	pv_ops.time.steal_clock = xen_steal_clock;
> +	static_call_update(pv_steal_clock, xen_steal_clock);
>  

Do we actually need this? We've already set this up in xen_init_time_ops(). (But maybe for ARM).

-boris

>  	static_key_slow_inc(&paravirt_steal_enabled);
>  	if (xen_runstate_remote)