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SubjectRe: [PATCH v3 3/4] xen: Mark "xen_nopvspin" parameter obsolete and map it to "nopvspin"
On Mon, Sep 30, 2019 at 08:44:38PM +0800, Zhenzhong Duan wrote:
> Fix stale description of "xen_nopvspin" as we use qspinlock now.
>
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
> Reviewed-by: Juergen Gross <jgross@suse.com>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Cc: Juergen Gross <jgross@suse.com>
> Cc: Stefano Stabellini <sstabellini@kernel.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> ---
> Documentation/admin-guide/kernel-parameters.txt | 7 ++++---
> arch/x86/xen/spinlock.c | 13 +++++++------
> 2 files changed, 11 insertions(+), 9 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 4b956d8..1f0a62f 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -5303,8 +5303,9 @@
> never -- do not unplug even if version check succeeds
>
> xen_nopvspin [X86,XEN]
> - Disables the ticketlock slowpath using Xen PV
> - optimizations.
> + Disables the qspinlock slowpath using Xen PV optimizations.
> + This parameter is obsoleted by "nopvspin" parameter, which
> + has equivalent effect for XEN platform.
>
> xen_nopv [X86]
> Disables the PV optimizations forcing the HVM guest to
> @@ -5330,7 +5331,7 @@
> as generic guest with no PV drivers. Currently support
> XEN HVM, KVM, HYPER_V and VMWARE guest.
>
> - nopvspin [X86,KVM] Disables the qspinlock slow path
> + nopvspin [X86,XEN,KVM] Disables the qspinlock slow path
> using PV optimizations which allow the hypervisor to
> 'idle' the guest on lock contention.
>
> diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
> index 6deb490..092a53f 100644
> --- a/arch/x86/xen/spinlock.c
> +++ b/arch/x86/xen/spinlock.c
> @@ -18,7 +18,6 @@
> static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
> static DEFINE_PER_CPU(char *, irq_name);
> static DEFINE_PER_CPU(atomic_t, xen_qlock_wait_nest);
> -static bool xen_pvspin = true;
>
> static void xen_qlock_kick(int cpu)
> {
> @@ -68,7 +67,7 @@ void xen_init_lock_cpu(int cpu)
> int irq;
> char *name;
>
> - if (!xen_pvspin)
> + if (!pvspin)
> return;
>
> WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n",
> @@ -93,7 +92,7 @@ void xen_init_lock_cpu(int cpu)
>
> void xen_uninit_lock_cpu(int cpu)
> {
> - if (!xen_pvspin)
> + if (!pvspin)
> return;
>
> unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL);
> @@ -117,9 +116,9 @@ void __init xen_init_spinlocks(void)
>
> /* Don't need to use pvqspinlock code if there is only 1 vCPU. */
> if (num_possible_cpus() == 1)
> - xen_pvspin = false;
> + pvspin = false;

As suggested in the other patch, if you incorporate pvspin (or nopvspin)
into xen_pvspin then the param can be __initdata and the diff for this
patch will be smaller, e.g. you wouldn't need the xen_domain() shenanigans
in xen_parse_nopvspin().

> - if (!xen_pvspin) {
> + if (!pvspin) {
> printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
> static_branch_disable(&virt_spin_lock_key);
> return;
> @@ -137,7 +136,9 @@ void __init xen_init_spinlocks(void)
>
> static __init int xen_parse_nopvspin(char *arg)
> {
> - xen_pvspin = false;
> + pr_notice("\"xen_nopvspin\" is deprecated, please use \"nopvspin\" instead\n");
> + if (xen_domain())
> + pvspin = false;
> return 0;
> }
> early_param("xen_nopvspin", xen_parse_nopvspin);
> --
> 1.8.3.1
>

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