/* * Copyright (c) 2010 Apple Inc. All rights reserved. * * @APPLE_LICENSE_HEADER_START@ * * This file contains Original Code and/or Modifications of Original Code * as defined in and that are subject to the Apple Public Source License * Version 2.0 (the 'License'). You may not use this file except in * compliance with the License. Please obtain a copy of the License at * http://www.opensource.apple.com/apsl/ and read it before using this * file. * * The Original Code and all software distributed under the License are * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT. * Please see the License for the specific language governing rights and * limitations under the License. * * @APPLE_LICENSE_HEADER_END@ */ #include <machine/cpu_capabilities.h> #include <mach/i386/syscall_sw.h> /* Subroutine to make a preempt syscall. Called when we notice %ebx is * nonzero after returning from a PFZ subroutine. * When we enter kernel: * %edx = return address * %ecx = stack ptr * Destroys %eax, %ecx, and %edx. */ .align 4 .private_extern _preempt _preempt: popl %edx // get return address movl %esp,%ecx // save stack ptr here movl $(-58),%eax /* 58 = pfz_exit */ xorl %ebx,%ebx // clear "preemption pending" flag sysenter /* Subroutine to back off if we cannot get the spinlock. Called * after a few attempts inline in the PFZ subroutines. This code is * not in the PFZ. * %edi = ptr to queue head structure * %ebx = preemption flag (nonzero if preemption pending) * Destroys %eax. */ .align 4 .private_extern _backoff _backoff: testl %ebx,%ebx // does kernel want to preempt us? jz 1f // no xorl %ebx,%ebx // yes, clear flag pushl %edx // preserve regs used by preempt syscall pushl %ecx call _preempt popl %ecx popl %edx 1: pause // SMT-friendly backoff cmpl $0,8(%edi) // sniff the lockword jnz 1b // loop if still taken ret // lockword is free, so reenter PFZ