From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752641AbbAKWGn (ORCPT ); Sun, 11 Jan 2015 17:06:43 -0500 Received: from shelob.surriel.com ([74.92.59.67]:38186 "EHLO shelob.surriel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752300AbbAKWF2 (ORCPT ); Sun, 11 Jan 2015 17:05:28 -0500 From: riel@redhat.com To: linux-kernel@vger.kernel.org Cc: mingo@redhat.com, hpa@zytor.com, matt.fleming@intel.com, bp@suse.de, oleg@redhat.com, pbonzini@redhat.com, tglx@linutronix.de, luto@amacapital.net Subject: [RFC PATCH 06/11] x86,fpu: lazily skip fpu restore with eager fpu mode, too Date: Sun, 11 Jan 2015 16:46:28 -0500 Message-Id: <1421012793-30106-7-git-send-email-riel@redhat.com> X-Mailer: git-send-email 1.9.3 In-Reply-To: <1421012793-30106-1-git-send-email-riel@redhat.com> References: <1421012793-30106-1-git-send-email-riel@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Rik van Riel If the next task still has its FPU state present in the FPU registers, there is no need to restore it from memory. This is no big deal on bare metal, where XSAVEOPT / XRSTOR are heavily optimized, but those optimizations do not carry across VMENTER / VMEXIT. Skipping the call to fpu_restore_checking when the FPU state is already loaded in the CPU could save a little bit of overhead on bare metal too, so this is not just a KVM optimization. Signed-off-by: Rik van Riel --- arch/x86/include/asm/fpu-internal.h | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/arch/x86/include/asm/fpu-internal.h b/arch/x86/include/asm/fpu-internal.h index 4db8781..a5a40c7 100644 --- a/arch/x86/include/asm/fpu-internal.h +++ b/arch/x86/include/asm/fpu-internal.h @@ -435,13 +435,9 @@ static inline void switch_fpu_prepare(struct task_struct *old, struct task_struc old->thread.fpu.last_cpu = ~0; if (preload) { new->thread.fpu_counter++; - if (!use_eager_fpu() && fpu_lazy_restore(new, cpu)) - /* XXX: is this safe against ptrace??? */ - __thread_fpu_begin(new); - else { + set_thread_flag(TIF_LOAD_FPU); + if (!fpu_lazy_restore(new, cpu)) prefetch(new->thread.fpu.state); - set_thread_flag(TIF_LOAD_FPU); - } } else /* * The new task does not want an FPU state restore, @@ -466,6 +462,10 @@ static inline void switch_fpu_finish(void) __thread_fpu_begin(tsk); + /* The FPU registers already have this task's FPU state. */ + if (fpu_lazy_restore(tsk, raw_smp_processor_id())) + return; + if (unlikely(restore_fpu_checking(tsk))) drop_init_fpu(tsk); } -- 1.9.3