From: Peter Zijlstra <peterz@infradead.org> To: Waiman Long <longman@redhat.com> Cc: hpa@zytor.com, "Jeremy Fitzhardinge" <jeremy@goop.org>, "Chris Wright" <chrisw@sous-sol.org>, "Alok Kataria" <akataria@vmware.com>, "Rusty Russell" <rusty@rustcorp.com.au>, "Ingo Molnar" <mingo@redhat.com>, "Thomas Gleixner" <tglx@linutronix.de>, linux-arch@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, xen-devel@lists.xenproject.org, kvm@vger.kernel.org, "Pan Xinhui" <xinhui.pan@linux.vnet.ibm.com>, "Paolo Bonzini" <pbonzini@redhat.com>, "Radim Krčmář" <rkrcmar@redhat.com>, "Boris Ostrovsky" <boris.ostrovsky@oracle.com>, "Juergen Gross" <jgross@suse.com> Subject: Re: [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function Date: Mon, 13 Feb 2017 23:31:30 +0100 [thread overview] Message-ID: <20170213223130.GL6500@twins.programming.kicks-ass.net> (raw) In-Reply-To: <19008130-7b73-5c53-3cb5-a013e9e5552b@redhat.com> On Mon, Feb 13, 2017 at 05:24:36PM -0500, Waiman Long wrote: > >> movsql %edi, %rax; > >> movq __per_cpu_offset(,%rax,8), %rax; > >> cmpb $0, %[offset](%rax); > >> setne %al; > I have thought of that too. However, the goal is to eliminate memory > read/write from/to stack. Eliminating a register sign-extend instruction > won't help much in term of performance. Problem here is that all instructions have dependencies, so if you can get rid of the sign extend mov you kill a bunch of stall cycles (I would expect). But yes, peanuts vs the stack load/stores.
WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org> To: Waiman Long <longman@redhat.com> Cc: linux-arch@vger.kernel.org, "Juergen Gross" <jgross@suse.com>, "Jeremy Fitzhardinge" <jeremy@goop.org>, x86@kernel.org, kvm@vger.kernel.org, "Radim Krčmář" <rkrcmar@redhat.com>, "Boris Ostrovsky" <boris.ostrovsky@oracle.com>, "Pan Xinhui" <xinhui.pan@linux.vnet.ibm.com>, "Paolo Bonzini" <pbonzini@redhat.com>, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, "Chris Wright" <chrisw@sous-sol.org>, "Ingo Molnar" <mingo@redhat.com>, hpa@zytor.com, xen-devel@lists.xenproject.org, "Alok Kataria" <akataria@vmware.com>, "Thomas Gleixner" <tglx@linutronix.de> Subject: Re: [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function Date: Mon, 13 Feb 2017 23:31:30 +0100 [thread overview] Message-ID: <20170213223130.GL6500@twins.programming.kicks-ass.net> (raw) In-Reply-To: <19008130-7b73-5c53-3cb5-a013e9e5552b@redhat.com> On Mon, Feb 13, 2017 at 05:24:36PM -0500, Waiman Long wrote: > >> movsql %edi, %rax; > >> movq __per_cpu_offset(,%rax,8), %rax; > >> cmpb $0, %[offset](%rax); > >> setne %al; > I have thought of that too. However, the goal is to eliminate memory > read/write from/to stack. Eliminating a register sign-extend instruction > won't help much in term of performance. Problem here is that all instructions have dependencies, so if you can get rid of the sign extend mov you kill a bunch of stall cycles (I would expect). But yes, peanuts vs the stack load/stores.
next prev parent reply other threads:[~2017-02-13 22:31 UTC|newest] Thread overview: 69+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-02-10 15:43 [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function Waiman Long 2017-02-10 15:43 ` Waiman Long 2017-02-10 16:19 ` Peter Zijlstra 2017-02-10 16:19 ` Peter Zijlstra 2017-02-10 16:19 ` Peter Zijlstra 2017-02-10 16:35 ` Waiman Long 2017-02-10 16:35 ` Waiman Long 2017-02-10 17:00 ` Waiman Long 2017-02-10 17:00 ` Waiman Long 2017-02-10 17:00 ` Waiman Long 2017-02-13 10:47 ` Peter Zijlstra 2017-02-13 10:47 ` Peter Zijlstra 2017-02-13 10:47 ` Peter Zijlstra 2017-02-13 10:53 ` Peter Zijlstra 2017-02-13 10:53 ` Peter Zijlstra 2017-02-13 10:53 ` Peter Zijlstra 2017-02-13 19:42 ` Waiman Long 2017-02-13 19:42 ` Waiman Long 2017-02-13 19:42 ` Waiman Long 2017-02-13 20:12 ` Waiman Long 2017-02-13 20:12 ` Waiman Long 2017-02-13 21:52 ` Peter Zijlstra 2017-02-13 21:52 ` Peter Zijlstra 2017-02-13 21:52 ` Peter Zijlstra 2017-02-13 22:00 ` hpa 2017-02-13 22:00 ` hpa 2017-02-13 22:00 ` hpa 2017-02-13 22:07 ` hpa 2017-02-13 22:07 ` hpa 2017-02-13 22:07 ` hpa 2017-02-13 22:34 ` Waiman Long 2017-02-13 22:34 ` Waiman Long 2017-02-13 22:34 ` Waiman Long 2017-02-13 22:36 ` hpa 2017-02-13 22:36 ` hpa 2017-02-13 22:36 ` hpa 2017-02-14 9:39 ` Peter Zijlstra 2017-02-14 9:39 ` Peter Zijlstra 2017-02-14 9:39 ` Peter Zijlstra 2017-02-14 14:46 ` Waiman Long 2017-02-14 14:46 ` Waiman Long 2017-02-14 14:46 ` Waiman Long 2017-02-14 16:03 ` Peter Zijlstra 2017-02-14 16:03 ` Peter Zijlstra 2017-02-14 16:03 ` Peter Zijlstra 2017-02-14 16:18 ` [Xen-devel] " Andrew Cooper 2017-02-14 16:18 ` Andrew Cooper 2017-02-14 16:18 ` [Xen-devel] " Andrew Cooper 2017-02-13 20:12 ` Waiman Long 2017-02-13 20:06 ` hpa 2017-02-13 20:06 ` hpa 2017-02-13 21:57 ` Peter Zijlstra 2017-02-13 21:57 ` Peter Zijlstra 2017-02-13 21:57 ` Peter Zijlstra 2017-02-13 22:24 ` Waiman Long 2017-02-13 22:24 ` Waiman Long 2017-02-13 22:31 ` Peter Zijlstra 2017-02-13 22:31 ` Peter Zijlstra [this message] 2017-02-13 22:31 ` Peter Zijlstra 2017-02-13 22:24 ` Waiman Long 2017-02-13 20:06 ` hpa 2017-02-13 19:41 ` Waiman Long 2017-02-13 19:41 ` Waiman Long 2017-02-13 19:41 ` Waiman Long 2017-02-10 16:35 ` Waiman Long 2017-02-10 16:22 ` Paolo Bonzini 2017-02-10 16:22 ` Paolo Bonzini 2017-02-10 16:22 ` Paolo Bonzini -- strict thread matches above, loose matches on Subject: below -- 2017-02-10 15:43 Waiman Long
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