From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 7EFBD2C for ; Fri, 22 Jul 2016 15:59:50 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.9]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 3135E2A1 for ; Fri, 22 Jul 2016 15:59:50 +0000 (UTC) Message-ID: <1469203184.120686.212.camel@infradead.org> From: David Woodhouse To: Christian Borntraeger , David Howells , ksummit-discuss@lists.linuxfoundation.org Date: Fri, 22 Jul 2016 16:59:44 +0100 In-Reply-To: <5792414F.5040902@de.ibm.com> References: <15569.1469184060@warthog.procyon.org.uk> <5792414F.5040902@de.ibm.com> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-5UO//ErtZY8xdeECJXI4" Mime-Version: 1.0 Subject: Re: [Ksummit-discuss] [TECH TOPIC] Compiler shopping list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , --=-5UO//ErtZY8xdeECJXI4 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Fri, 2016-07-22 at 17:52 +0200, Christian Borntraeger wrote: > On 07/22/2016 12:41 PM, David Howells wrote: > > Are there additional things we can get the compiler to do for us? Some > > things I've seen brought up: > >=20 > > (1) Additional __atomic_*() ops could be useful. Suggestions I've hea= rd > > include direct LL/SC support - though the compiler people don't se= em so > > keen on that. > >=20 > > (2) -mmodel=3Dkernel flag so that the compiler can optimise better for= the > > kernel memory model. >=20 > Some years ago (actually many) Linus proposed to have an endianess attrib= ute to data > types, so that the compiler can do the bswap automatically. For some reas= on this > was never implemented, but this might be a good idea anyway. >=20 > e.g.=20 >=20 > unsigned long x[10] __attribute__(("bigendian")); I'm not sure Linus proposed that. I certainly did, many times. With the work I put in to make use of __builtin_bswapXX() we do have a *certain* amount of the functionality that full endianness attribution would give us =E2=80=94 the compiler can see and optimise certain load/mask/save operations, and can use movbe and equivalent instructions. But a full implementation that let us just do assignment without jumping through the hoops might still be nice. --=20 dwmw2 --=-5UO//ErtZY8xdeECJXI4 Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCEeAw ggXiMIIDyqADAgECAhBrp4p9CteI1lEK+Vnk57ThMA0GCSqGSIb3DQEBCwUAMH0xCzAJBgNVBAYT AklMMRYwFAYDVQQKEw1TdGFydENvbSBMdGQuMSswKQYDVQQLEyJTZWN1cmUgRGlnaXRhbCBDZXJ0 aWZpY2F0ZSBTaWduaW5nMSkwJwYDVQQDEyBTdGFydENvbSBDZXJ0aWZpY2F0aW9uIEF1dGhvcml0 eTAeFw0xNTEyMTYwMTAwMDVaFw0zMDEyMTYwMTAwMDVaMHUxCzAJBgNVBAYTAklMMRYwFAYDVQQK Ew1TdGFydENvbSBMdGQuMSkwJwYDVQQLEyBTdGFydENvbSBDZXJ0aWZpY2F0aW9uIEF1dGhvcml0 eTEjMCEGA1UEAxMaU3RhcnRDb20gQ2xhc3MgMSBDbGllbnQgQ0EwggEiMA0GCSqGSIb3DQEBAQUA A4IBDwAwggEKAoIBAQC9fdr3w6J9g/Zbgv3bW1+uHht1wLUZr5gkrLtXedg17AkefMyUGwrQdvwO bhajcVmnKVxhrUwkZPXRAwZZosRHfEIi5FH7x6SV/8Sp5lZEuiMnvMFG2MzLA84J6Ws5T4NfXZ0q 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