From: Sasha Levin <sashal@kernel.org>
To: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de,
mingo@kernel.org, bp@alien8.de, hpa@zytor.com,
boris.ostrovsky@oracle.com, jgross@suse.com,
sstabellini@kernel.org, peterz@infradead.org,
srinivas.eeda@oracle.com, Waiman Long <longman@redhat.com>,
"K. Y. Srinivasan" <kys@microsoft.com>,
Haiyang Zhang <haiyangz@microsoft.com>,
Stephen Hemminger <sthemmin@microsoft.com>,
Ingo Molnar <mingo@redhat.com>,
linux-hyperv@vger.kernel.org
Subject: Re: [PATCH v2 6/7] locking/spinlocks, paravirt, hyperv: Correct the hv_nopvspin case
Date: Thu, 27 Jun 2019 18:28:51 -0400 [thread overview]
Message-ID: <20190627222851.GC11506@sasha-vm> (raw)
In-Reply-To: <1561377779-28036-7-git-send-email-zhenzhong.duan@oracle.com>
On Mon, Jun 24, 2019 at 08:02:58PM +0800, Zhenzhong Duan wrote:
>With the boot parameter "hv_nopvspin" specified a Hyperv guest should
>not make use of paravirt spinlocks, but behave as if running on bare
>metal. This is not true, however, as the qspinlock code will fall back
>to a test-and-set scheme when it is detecting a hypervisor.
>
>In order to avoid this disable the virt_spin_lock_key.
>
>Same change for XEN is already in Commit e6fd28eb3522
>("locking/spinlocks, paravirt, xen: Correct the xen_nopvspin case")
>
>Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
>Cc: Waiman Long <longman@redhat.com>
>Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
>Cc: "K. Y. Srinivasan" <kys@microsoft.com>
>Cc: Haiyang Zhang <haiyangz@microsoft.com>
>Cc: Stephen Hemminger <sthemmin@microsoft.com>
>Cc: Sasha Levin <sashal@kernel.org>
>Cc: Thomas Gleixner <tglx@linutronix.de>
>Cc: Ingo Molnar <mingo@redhat.com>
>Cc: Borislav Petkov <bp@alien8.de>
>Cc: linux-hyperv@vger.kernel.org
>---
> arch/x86/hyperv/hv_spinlock.c | 3 +++
> 1 file changed, 3 insertions(+)
>
>diff --git a/arch/x86/hyperv/hv_spinlock.c b/arch/x86/hyperv/hv_spinlock.c
>index 07f21a0..d90b4b0 100644
>--- a/arch/x86/hyperv/hv_spinlock.c
>+++ b/arch/x86/hyperv/hv_spinlock.c
>@@ -64,6 +64,9 @@ __visible bool hv_vcpu_is_preempted(int vcpu)
>
> void __init hv_init_spinlocks(void)
> {
>+ if (unlikely(!hv_pvspin))
>+ static_branch_disable(&virt_spin_lock_key);
This should be combined in the conditional under it, which already
attempts to disable PV spinlocks, note how hv_pvspin is checked there.
hc_pvspin isn't the only reason we would disable PV spinlocks on hyperv.
Also, there's no need for the unlikely() here, it's only getting called
once...
--
Thanks,
Sasha
next prev parent reply other threads:[~2019-06-27 22:28 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-24 12:02 [PATCH v2 0/7] misc fixes to PV extentions code Zhenzhong Duan
2019-06-24 12:02 ` [PATCH v2 1/7] x86/xen: Mark xen_hvm_need_lapic() and xen_hvm_need_lapic() as __init Zhenzhong Duan
2019-06-24 12:02 ` [PATCH v2 2/7] x86/jailhouse: Mark jailhouse_x2apic_available " Zhenzhong Duan
2019-06-24 12:02 ` [PATCH v2 3/7] x86: Add nopv parameter to disable PV extensions Zhenzhong Duan
2019-06-26 9:38 ` Juergen Gross
2019-06-24 12:02 ` [PATCH v2 4/7] Revert "xen: Introduce 'xen_nopv' to disable PV extensions for HVM guests." Zhenzhong Duan
2019-06-26 9:39 ` Juergen Gross
2019-06-26 13:48 ` Thomas Gleixner
2019-06-24 12:02 ` [PATCH v2 5/7] x86/xen: nopv parameter support for HVM guest Zhenzhong Duan
2019-06-25 12:31 ` Juergen Gross
2019-06-26 8:56 ` Zhenzhong Duan
2019-06-26 9:03 ` Juergen Gross
2019-06-24 12:02 ` [PATCH v2 6/7] locking/spinlocks, paravirt, hyperv: Correct the hv_nopvspin case Zhenzhong Duan
2019-06-27 22:28 ` Sasha Levin [this message]
2019-06-28 0:53 ` Zhenzhong Duan
2019-06-24 12:02 ` [PATCH v2 7/7] Revert "x86/paravirt: Set up the virt_spin_lock_key after static keys get initialized" Zhenzhong Duan
2019-06-26 13:39 ` [PATCH v2 0/7] misc fixes to PV extentions code Thomas Gleixner
2019-06-27 8:47 ` Zhenzhong Duan
2019-06-27 12:24 ` Thomas Gleixner
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