Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752253AbbEFTKd (ORCPT ); Wed, 6 May 2015 15:10:33 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44034 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751197AbbEFTKa (ORCPT ); Wed, 6 May 2015 15:10:30 -0400 Message-ID: <554A6706.8010709@redhat.com> Date: Wed, 06 May 2015 21:09:58 +0200 From: Denys Vlasenko User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: "H. Peter Anvin" , Ingo Molnar CC: Steven Rostedt , Borislav Petkov , Andy Lutomirski , Frederic Weisbecker , Alexei Starovoitov , Will Drewry , Kees Cook , x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] x86: Deinline cpuid_eax and friends References: <1430932057-26574-1-git-send-email-dvlasenk@redhat.com> <554A649C.8070605@zytor.com> In-Reply-To: <554A649C.8070605@zytor.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2025 Lines: 45 On 05/06/2015 08:59 PM, H. Peter Anvin wrote: > On 05/06/2015 10:07 AM, Denys Vlasenko wrote: >> cpuid_e{a,b,c,d}x() functions compile to 44 bytes of machine code each. >> On x86 allyesconfig build they have 48 callsites. >> Deinlining all four of them shrinks kernel by about 1k: >> >> text data bss dec hex filename >> 82434909 22255384 20627456 125317749 7783275 vmlinux.before >> 82433898 22255384 20627456 125316738 7782e82 vmlinux >> >> Speed impact: CPUID instruction takes from 50 to 350+ cycles, >> call overhead is negligible in comparison. > > How on Earth does it make 44 bytes? Is this due to paravirt_fail? No, just this construct unsigned int eax, ebx, ecx, edx; cpuid(op, &eax, &ebx, &ecx, &edx); is not really that cheap to set up. You need to allocate variables on stack and take address of each: ffffffff81063668 : ffffffff81063668: 55 push %rbp ffffffff81063669: 48 89 e5 mov %rsp,%rbp ffffffff8106366c: 48 83 ec 10 sub $0x10,%rsp ffffffff81063670: 48 8d 4d fc lea -0x4(%rbp),%rcx ffffffff81063674: 89 7d f0 mov %edi,-0x10(%rbp) ffffffff81063677: 48 8d 55 f8 lea -0x8(%rbp),%rdx ffffffff8106367b: 48 8d 75 f4 lea -0xc(%rbp),%rsi ffffffff8106367f: 48 8d 7d f0 lea -0x10(%rbp),%rdi ffffffff81063683: c7 45 f8 00 00 00 00 movl $0x0,-0x8(%rbp) ffffffff8106368a: e8 3c ff ff ff callq ffffffff810635cb <__cpuid> ffffffff8106368f: 8b 45 f0 mov -0x10(%rbp),%eax ffffffff81063692: c9 leaveq ffffffff81063693: c3 retq -- vda -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/