From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752148AbbINRuT (ORCPT ); Mon, 14 Sep 2015 13:50:19 -0400 Received: from mail-io0-f175.google.com ([209.85.223.175]:32914 "EHLO mail-io0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750975AbbINRuP (ORCPT ); Mon, 14 Sep 2015 13:50:15 -0400 Subject: Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal due to a kernel NULL pointer dereference) To: sedat.dilek@gmail.com, Peter Zijlstra References: <20150909032541.GC1998@dhcp-17-102.nay.redhat.com> <20150909071410.GD1998@dhcp-17-102.nay.redhat.com> <20150909125424.GP3644@twins.programming.kicks-ass.net> <20150914071231.GM18489@twins.programming.kicks-ass.net> Cc: Baoquan He , Denys Vlasenko , Tejun Heo , Christoph Lameter , LKML , Andrew Morton , David Rientjes , Linus Torvalds , Thomas Gleixner , Thomas Graf , Ingo Molnar , the arch/x86 maintainers From: Austin S Hemmelgarn Message-ID: <55F708D3.9090007@gmail.com> Date: Mon, 14 Sep 2015 13:50:11 -0400 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-512; boundary="------------ms050506000400060900040409" X-Antivirus: avast! (VPS 150914-0, 2015-09-14), Outbound message X-Antivirus-Status: Clean Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is a cryptographically signed message in MIME format. --------------ms050506000400060900040409 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 2015-09-14 03:49, Sedat Dilek wrote: > On Mon, Sep 14, 2015 at 9:12 AM, Peter Zijlstra = wrote: >> On Sun, Sep 13, 2015 at 04:33:39AM +0200, Sedat Dilek wrote: >>>> It looks like an inline-optimization bug in CLANG when the compiler'= s >>>> optimization-level is higher than -O2. >> >>>> [1] http://lists.linuxfoundation.org/pipermail/llvmlinux/2015-Septem= ber/001355.html >>> >>> After some discussion on #llvm it turned out to be a known issue in L= LVMLinux! >>> >>> Unfortunately, an existing patch [1] got archived which is still >>> required to build x86_64 correctly. >> >>> [1] http://git.linuxfoundation.org/?p=3Dllvmlinux.git;a=3Dblob_plain;= f=3Darch/x86_64/patches/ARCHIVE/0029-Fix-ARCH_HWEIGHT-for-compilation-wit= h-clang.patch;hb=3DHEAD >> >> As long as LLVM cannot do things like that and requires full function >> calls I cannot see it being a sensible compiler to use from a >> performance POV. >> >> There's a fairly large difference between an inline POPCNT instruction= >> and a full out-of-line function call. >> >> /me goes back to ignoring LLVM for the time being. > > Can you give an example or describe a test-case to check the performanc= e? > > I have here diverse Linux v4.2 kernels (all have the same kernel-config= )... > > [ llvmlinux-patched ] > > #1: Compiled with CLANG v3.7 from a self-built llvm-toolchain v3.7.0 > #2: Compiled with GCC v4.9 > > [ unpatched ] > > #3: Compiled with GCC v4.9 > > Can you also comment on the effects of CONFIG_CC_OPTIMIZE_FOR_SIZE in > case of performance? > It is only to reduce binary size or does it also do some "speed" optimi= zation? I can comment at least a little about the -Os aspect (although not I'm=20 no expert on this in particular). In general, for _most_ use cases, a=20 kernel compiled with CONFIG_CC_OPTIMIZE_FOR_SIZE will run slower than=20 one compiled without it. On rare occasion though, it may actually run=20 faster, the only cases I've seen where this happens are specialized uses = that are very memory pressure dependent and run almost entirely in=20 userspace with almost no syscalls (for example math related stuff=20 operating on _very, very big_ (as in, >1 trillion elements)=20 multidimensional matrices, with complex memory constraints), and even=20 then it's usually a miniscule improvement in performance (generally less = than 1%, which can of course be significant depending on how long it=20 takes before the improvement). --------------ms050506000400060900040409 Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="smime.p7s" Content-Description: S/MIME Cryptographic Signature MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgMFADCABgkqhkiG9w0BBwEAAKCC Brgwgga0MIIEnKADAgECAgMQblUwDQYJKoZIhvcNAQENBQAweTEQMA4GA1UEChMHUm9vdCBD QTEeMBwGA1UECxMVaHR0cDovL3d3dy5jYWNlcnQub3JnMSIwIAYDVQQDExlDQSBDZXJ0IFNp Z25pbmcgQXV0aG9yaXR5MSEwHwYJKoZIhvcNAQkBFhJzdXBwb3J0QGNhY2VydC5vcmcwHhcN MTUwMzI1MTkzNDM4WhcNMTUwOTIxMTkzNDM4WjBjMRgwFgYDVQQDEw9DQWNlcnQgV29UIFVz ZXIxIzAhBgkqhkiG9w0BCQEWFGFoZmVycm9pbjdAZ21haWwuY29tMSIwIAYJKoZIhvcNAQkB FhNhaGVtbWVsZ0BvaGlvZ3QuY29tMIICIjANBgkqhkiG9w0BAQEFAAOCAg8AMIICCgKCAgEA nQ/81tq0QBQi5w316VsVNfjg6kVVIMx760TuwA1MUaNQgQ3NyUl+UyFtjhpkNwwChjgAqfGd LIMTHAdObcwGfzO5uI2o1a8MHVQna8FRsU3QGouysIOGQlX8jFYXMKPEdnlt0GoQcd+BtESr pivbGWUEkPs1CwM6WOrs+09bAJP3qzKIr0VxervFrzrC5Dg9Rf18r9WXHElBuWHg4GYHNJ2V Ab8iKc10h44FnqxZK8RDN8ts/xX93i9bIBmHnFfyNRfiOUtNVeynJbf6kVtdHP+CRBkXCNRZ qyQT7gbTGD24P92PS2UTmDfplSBcWcTn65o3xWfesbf02jF6PL3BCrVnDRI4RgYxG3zFBJuG qvMoEODLhHKSXPAyQhwZINigZNdw5G1NqjXqUw+lIqdQvoPijK9J3eijiakh9u2bjWOMaleI SMRR6XsdM2O5qun1dqOrCgRkM0XSNtBQ2JjY7CycIx+qifJWsRaYWZz0aQU4ZrtAI7gVhO9h pyNaAGjvm7PdjEBiXq57e4QcgpwzvNlv8pG1c/hnt0msfDWNJtl3b6elhQ2Pz4w/QnWifZ8E BrFEmjeeJa2dqjE3giPVWrsH+lOvQQONsYJOuVb8b0zao4vrWeGmW2q2e3pdv0Axzm/60cJQ haZUv8+JdX9ZzqxOm5w5eUQSclt84u+D+hsCAwEAAaOCAVkwggFVMAwGA1UdEwEB/wQCMAAw VgYJYIZIAYb4QgENBEkWR1RvIGdldCB5b3VyIG93biBjZXJ0aWZpY2F0ZSBmb3IgRlJFRSBo ZWFkIG92ZXIgdG8gaHR0cDovL3d3dy5DQWNlcnQub3JnMA4GA1UdDwEB/wQEAwIDqDBABgNV HSUEOTA3BggrBgEFBQcDBAYIKwYBBQUHAwIGCisGAQQBgjcKAwQGCisGAQQBgjcKAwMGCWCG SAGG+EIEATAyBggrBgEFBQcBAQQmMCQwIgYIKwYBBQUHMAGGFmh0dHA6Ly9vY3NwLmNhY2Vy dC5vcmcwMQYDVR0fBCowKDAmoCSgIoYgaHR0cDovL2NybC5jYWNlcnQub3JnL3Jldm9rZS5j cmwwNAYDVR0RBC0wK4EUYWhmZXJyb2luN0BnbWFpbC5jb22BE2FoZW1tZWxnQG9oaW9ndC5j b20wDQYJKoZIhvcNAQENBQADggIBABr5e8W+NiTER+Q/7wiA2LxWN3UdhT3eZJjqqSlP370P KL5iWqeTfxQ67Ai/mHbJcT2PgAJ+/D2Ji+aRR03UWnU/vtOwzyDLUMstqnfl0Zs+sz/CJe7x nBA5jlpjC2DKuMVfbPze7eySaen7XSGFHKE1QoVIIpQ2kVjC4nbbJQnUbAVX1Iz29WxeVGt9 XYigz3tDPf3tglN+q23E7YjQl4abTIoM7i98yV1H9gfY8lFfKZ6jREB9+n6ie2EwS3Kat2mG tl2wBx4MfRnoSQSKsLKQ5oTwhWf0JqlFwpLfl374p0Njcykej9/jnWG8Ks1V/AXTHqI4eyIP Mf5yMZkPv7n7LS9WWKdG4Nd38iv4T2EiAaWsmgu+r81qL5CJu9AyA0SBS4ttKf6k3e63w2Mv N9R45vpQ3QhAhfWyFxFhZN95APe3YECDG3+XIRJpRYPEtHuIsOyzI70ajF93gg/BidvqKsmV MM2ccktDMfqwZXea6zey7F8Geu9R7BqjXmG2HlNuXu7e/xnHOgXf5D3wPmnRLlBhXL1Ch97a w2KjaupjpAHfFjv5kGnZXN87UvvlwzIZiKXwa3vTDwK+rrKn/sHPkfDZPSiyt/ZBIK6lX83P 34H/CzGg+Kx57rHYOIHGumIvpDa5vfWp8O0sGgawb1C2Aae4sTUVIWmIjVuGI062MYIE0TCC BM0CAQEwgYAweTEQMA4GA1UEChMHUm9vdCBDQTEeMBwGA1UECxMVaHR0cDovL3d3dy5jYWNl cnQub3JnMSIwIAYDVQQDExlDQSBDZXJ0IFNpZ25pbmcgQXV0aG9yaXR5MSEwHwYJKoZIhvcN AQkBFhJzdXBwb3J0QGNhY2VydC5vcmcCAxBuVTANBglghkgBZQMEAgMFAKCCAiEwGAYJKoZI hvcNAQkDMQsGCSqGSIb3DQEHATAcBgkqhkiG9w0BCQUxDxcNMTUwOTE0MTc1MDExWjBPBgkq hkiG9w0BCQQxQgRAglfcxzuxGEpOWVmxDqFiiBWpfW/NVExBcIkXArS5W7TxEngRio9jOvUf 8HU8RROJ03Yzr42jwjneRu+jbWXKCDBsBgkqhkiG9w0BCQ8xXzBdMAsGCWCGSAFlAwQBKjAL BglghkgBZQMEAQIwCgYIKoZIhvcNAwcwDgYIKoZIhvcNAwICAgCAMA0GCCqGSIb3DQMCAgFA MAcGBSsOAwIHMA0GCCqGSIb3DQMCAgEoMIGRBgkrBgEEAYI3EAQxgYMwgYAweTEQMA4GA1UE ChMHUm9vdCBDQTEeMBwGA1UECxMVaHR0cDovL3d3dy5jYWNlcnQub3JnMSIwIAYDVQQDExlD QSBDZXJ0IFNpZ25pbmcgQXV0aG9yaXR5MSEwHwYJKoZIhvcNAQkBFhJzdXBwb3J0QGNhY2Vy dC5vcmcCAxBuVTCBkwYLKoZIhvcNAQkQAgsxgYOggYAweTEQMA4GA1UEChMHUm9vdCBDQTEe MBwGA1UECxMVaHR0cDovL3d3dy5jYWNlcnQub3JnMSIwIAYDVQQDExlDQSBDZXJ0IFNpZ25p bmcgQXV0aG9yaXR5MSEwHwYJKoZIhvcNAQkBFhJzdXBwb3J0QGNhY2VydC5vcmcCAxBuVTAN BgkqhkiG9w0BAQEFAASCAgAR6cW5oSRRIDnO/aMLaO0oWRcbAccKP/PttGlec1WH6KByxpRv D7JVEeuOJjdFISHzny+nOew/Xj1ZFOlP6ZqIMBPd08Exo7ZOcQgIioEj+SJzfXa7EK7IWOD/ M2sXwVH5sIH03iQLUAKlGdiz9xexS/28ZpSgnk1jhYLRHLsYq+uYtZKeVf6/KDFZ507MWzY7 9N54LXIl2JDBu9TbhqoeMudD0PI8Ug5R2dVknqQLFu9EV4TxjJ7/OEkv48au8+xEijjtmZWK DdH46OozJH4vG/iwVyvF2+uIvHqqxEEt/Qe9zXeeT5a+nokjQNE2cC2JOOYj+xxJCOigCQDJ JdjES+IH7seFrcLTaHrkuEHrVXDd9bjzUr2SwNrWWWky+fK1ex1QQ8PIF61Axt4r5D8gjSNk 3YSBIHOkM0su3NfpMPy+mMA9eFRHxv9aOmdRr/8wi0E6kXUh1XfLR89Xe+WJEz7RhgqFBGTe CyR4LAe1JHBACL+o6gL/lEBhLaIuWdUydwWOWX4mEfvJfXGPEM3zcMhKC7jnr5DkBerOM/h6 ClPEfhZp+NZNfKTj/FLYPSNTHwJcuPSN6Jkgv//4LmVLv8F7bTjSDlnvGsVM0UA6JB2mK1r+ j3ixUtDeJNElc9daDoS3xkDGNwpfQy33vPgpdcpdjrTRD2vb9gi5y92x9QAAAAAAAA== --------------ms050506000400060900040409--