From: Peter Zijlstra <peterz@infradead.org>
To: Pan Xinhui <xinhui@linux.vnet.ibm.com>
Cc: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>,
linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
virtualization@lists.linux-foundation.org,
linux-s390@vger.kernel.org,
xen-devel-request@lists.xenproject.org, kvm@vger.kernel.org,
xen-devel@lists.xenproject.org, x86@kernel.org,
benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au,
mingo@redhat.com, paulmck@linux.vnet.ibm.com,
will.deacon@arm.com, kernellwp@gmail.com, jgross@suse.com,
pbonzini@redhat.com, bsingharora@gmail.com, boqun.feng@gmail.com,
borntraeger@de.ibm.com, rkrcmar@redhat.com,
David.Laight@ACULAB.COM, dave@stgolabs.net,
konrad.wilk@oracle.com
Subject: Re: [PATCH v7 06/11] x86, paravirt: Add interface to support kvm/xen vcpu preempted check
Date: Wed, 16 Nov 2016 11:23:55 +0100 [thread overview]
Message-ID: <20161116102355.GP3142@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <a6026a0c-9ad8-5025-c616-eb33f96e91ce@linux.vnet.ibm.com>
On Wed, Nov 16, 2016 at 12:19:09PM +0800, Pan Xinhui wrote:
> Hi, Peter.
> I think we can avoid a function call in a simpler way. How about below
>
> static inline bool vcpu_is_preempted(int cpu)
> {
> /* only set in pv case*/
> if (pv_lock_ops.vcpu_is_preempted)
> return pv_lock_ops.vcpu_is_preempted(cpu);
> return false;
> }
That is still more expensive. It needs to do an actual load and makes it
hard to predict the branch, you'd have to actually wait for the load to
complete etc.
Also, it generates more code.
Paravirt muck should strive to be as cheap as possible when ran on
native hardware.
next prev parent reply other threads:[~2016-11-16 10:24 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-02 9:08 [PATCH v7 00/11] implement vcpu preempted check Pan Xinhui
2016-11-02 9:08 ` [PATCH v7 01/11] kernel/sched: introduce vcpu preempted check interface Pan Xinhui
2016-11-22 12:31 ` [tip:locking/core] sched/core: Introduce the vcpu_is_preempted(cpu) interface tip-bot for Pan Xinhui
2016-11-02 9:08 ` [PATCH v7 02/11] locking/osq: Drop the overload of osq_lock() Pan Xinhui
2016-11-22 12:36 ` [tip:locking/core] locking/osq: Break out of spin-wait busy waiting loop for a preempted vCPU in osq_lock() tip-bot for Pan Xinhui
2016-11-02 9:08 ` [PATCH v7 03/11] kernel/locking: Drop the overload of {mutex,rwsem}_spin_on_owner Pan Xinhui
2016-11-22 12:36 ` [tip:locking/core] locking/mutex: Break out of expensive busy-loop on {mutex,rwsem}_spin_on_owner() when owner vCPU is preempted tip-bot for Pan Xinhui
2016-11-02 9:08 ` [PATCH v7 04/11] powerpc/spinlock: support vcpu preempted check Pan Xinhui
2016-11-22 12:32 ` [tip:locking/core] locking/core, powerpc: Implement vcpu_is_preempted(cpu) tip-bot for Pan Xinhui
2016-11-02 9:08 ` [PATCH v7 05/11] s390/spinlock: Provide vcpu_is_preempted Pan Xinhui
2016-11-22 12:32 ` [tip:locking/core] locking/spinlocks, s390: Implement vcpu_is_preempted(cpu) tip-bot for Christian Borntraeger
2016-11-02 9:08 ` [PATCH v7 06/11] x86, paravirt: Add interface to support kvm/xen vcpu preempted check Pan Xinhui
2016-11-15 15:47 ` Peter Zijlstra
2016-11-16 4:19 ` Pan Xinhui
2016-11-16 10:23 ` Peter Zijlstra [this message]
2016-11-16 11:29 ` Christian Borntraeger
2016-11-16 11:43 ` Peter Zijlstra
2016-11-17 5:16 ` Pan Xinhui
2016-11-22 12:33 ` [tip:locking/core] locking/core, x86/paravirt: Implement vcpu_is_preempted(cpu) for KVM and Xen guests tip-bot for Pan Xinhui
2016-11-02 9:08 ` [PATCH v7 07/11] KVM: Introduce kvm_write_guest_offset_cached Pan Xinhui
2016-11-22 12:33 ` [tip:locking/core] kvm: Introduce kvm_write_guest_offset_cached() tip-bot for Pan Xinhui
2016-11-02 9:08 ` [PATCH v7 08/11] x86, kvm/x86.c: support vcpu preempted check Pan Xinhui
2016-11-22 12:34 ` [tip:locking/core] x86/kvm: Support the vCPU preemption check tip-bot for Pan Xinhui
2016-12-19 11:42 ` [PATCH v7 08/11] x86, kvm/x86.c: support vcpu preempted check Andrea Arcangeli
2016-12-19 13:56 ` Pan Xinhui
2016-12-19 14:39 ` Paolo Bonzini
2016-11-02 9:08 ` [PATCH v7 09/11] x86, kernel/kvm.c: " Pan Xinhui
2016-11-22 12:34 ` [tip:locking/core] x86/kvm: Support the vCPU preemption check tip-bot for Pan Xinhui
2016-11-02 9:08 ` [PATCH v7 10/11] x86, xen: support vcpu preempted check Pan Xinhui
2016-11-22 12:35 ` [tip:locking/core] x86/xen: Support the vCPU preemption check tip-bot for Juergen Gross
2016-11-02 9:08 ` [PATCH v7 11/11] Documentation: virtual: kvm: Support vcpu preempted check Pan Xinhui
2016-11-22 12:35 ` [tip:locking/core] Documentation/virtual/kvm: Support the vCPU preemption check tip-bot for Pan Xinhui
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