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Thu, 28 Jan 2021 07:27:32 +0000 Subject: Re: [PATCH 1/6] MIPS: Octeon: Implement __smp_store_release() To: Peter Zijlstra Cc: Paul Burton , linux-mips@vger.kernel.org, Thomas Bogendoerfer , Will Deacon , Boqun Feng , Ingo Molnar , linux-kernel@vger.kernel.org References: <20210127203627.47510-1-alexander.sverdlin@nokia.com> <20210127203627.47510-2-alexander.sverdlin@nokia.com> From: Alexander Sverdlin Message-ID: Date: Thu, 28 Jan 2021 08:27:29 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [131.228.32.169] X-ClientProxiedBy: AM0PR06CA0092.eurprd06.prod.outlook.com (2603:10a6:208:fa::33) To AM0PR07MB4531.eurprd07.prod.outlook.com (2603:10a6:208:6e::15) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from ulegcpsvhp1.emea.nsn-net.net (131.228.32.169) by AM0PR06CA0092.eurprd06.prod.outlook.com (2603:10a6:208:fa::33) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3805.16 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: =?utf-8?B?blRFZUZGSEFyckVzR3RxN0VvdGN4S0VNeEhHTjlrbTFMaFJ2dFVwMVdXVVNt?= =?utf-8?B?L0pRRGM1MDk3ZUpvT0o5c2I0blZERTlDZGl2cUlZNGJobUEyNnh5c1gxeWxy?= =?utf-8?B?TFpxaFlsdnMxRTNqcG9LbVhmOGZ0bjloT0t0OUYvOGVjT1NKLzFNbnlGbjdy?= =?utf-8?B?NzRCN3hIWTRkY1lpbkFZdHJOaEFQWGdUSUJOcDJ1UW8vaHQrVG9IVlBaNmlF?= =?utf-8?B?MzFoaEZvbVJIaWNXOENoKzJyRjhqcnBDRUp6eVZ1Ujd5VUpoQ2xUWFhUWTdi?= =?utf-8?B?d1FYbzJwRW9GMFZTWGNBampuZGNOY05WTWpjcjNDT2VmY05PdUUxUHVSOUIz?= =?utf-8?B?NExQZDl1SnByazdGaVBYRVZwdmJKR1RMTUhhMmhyTXFLTDVlZlcvY2ViMCt6?= =?utf-8?B?TGNNTHM1ekprYy96ZjZrbzhheDFTY0xkV1FPQWpxTm9OZFYxZEppNkhRL3N1?= =?utf-8?B?blF1VUl0VXh3M3RMVGVwMy9DYkZBNzhKNkl1N0Frd1U0Mko5c0JjZ1lEbG40?= =?utf-8?B?R2liVFVLOFd2dUc2S0U0ZWZYU3BPdUZQaGo4aDY3RWxrV09EcFVlNVg3UHE5?= =?utf-8?B?aENJbVdBbTZoeWtNZHorOXlBOHVhZWJ3WVJOL2xDUmd1eGdsU3VNRC9JU0RI?= =?utf-8?B?LzkvNWVhRHpscWQyWWZ2VDMvdmV6bGtndUphbW9qMWFybTN5LytVcFlmcTRR?= =?utf-8?B?b2czNDc2Y3YwUWZMZzJUbURldlpOSmowbzcyejdYOWEyN3pVTlkveUkySGxi?= =?utf-8?B?MHFaSkVCZy9pQ005WTZkUWtkSi96dmRoM1VpOUthTWNmdkRGS0V1b1hkeWVh?= =?utf-8?B?cGNZbHd4MzNscm5tVzNaNHF4Q1NleVNuSkprLzhNM0NrSUZxMHcza0N3UEkv?= =?utf-8?B?RVhaaDc3WnFuUldHMlJncUZyMitKRWZUVmQxcWVEOSsvZmdYVmMwYnpYTi9x?= =?utf-8?B?dWdaNmtsVi9SSDBkUk5rMFhhdE9EQUF0WGJyZ1FSU2dIcEF2eDNpMmxlbDRY?= =?utf-8?B?cVdPaVpQZXR1Zmd2aXRtSHFyK0s1YnErek5Kcm1CMU9kakUwQVpZdWdmRGxB?= =?utf-8?B?M0d1c1NiM1JkbU1sN2NOT0VmamRPVmhQOXE4dFNSM0pNczRTb3dDaUV2ajZN?= =?utf-8?B?SzRIa2ZjdVVCVHYrbjZKbjFVY0t0aFE2WWVBNnl4cUxIREhKcllySEFoVWo3?= =?utf-8?B?Ym5ONzJvcXBNblNMMjBGVExTdms5eE41UWpNeUNadm9obUFOZnJ4VTAyUzVa?= =?utf-8?B?T1NKZFlMcGdQazFCdmJNb1pTYkVhcFlIVEh3SEJNYTlCOFlXNVgrdGNQYWV5?= =?utf-8?B?eDFXMmhNaXkxeUxKZkM3RUFRRTg4ZDZNaDZmWmZ1eVBGY3NMMFVtSEpIK1Va?= =?utf-8?B?VHdLalpmQitXMkJUWUpCTmthbnFOSno5VWVvWTRCcHA1czFBMXBxaTlteEJN?= =?utf-8?Q?Hpbb3+4A?= X-OriginatorOrg: nokia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 648ce27d-7315-440e-5dd4-08d8c35e2d48 X-MS-Exchange-CrossTenant-AuthSource: AM0PR07MB4531.eurprd07.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 Jan 2021 07:27:32.9533 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 5d471751-9675-428d-917b-70f44f9630b0 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 55tYPNn4AvDvOgyrldXpsZoHMGtuOLk9YY9RoYyy85iJ/vgusTQH5MQRm0u9ACGkgSgd8HHKqWj2Ci4wcw5GGEHxsimoz0ZUYhGiVlfZGl4= X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM0PR07MB4468 Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org Hello Peter, On 27/01/2021 23:32, Peter Zijlstra wrote: >> Link: https://lore.kernel.org/lkml/5644D08D.4080206@caviumnetworks.com/ please, check the discussion pointed by the link above... >> Signed-off-by: Alexander Sverdlin >> --- >> arch/mips/include/asm/barrier.h | 9 +++++++++ >> 1 file changed, 9 insertions(+) >> >> diff --git a/arch/mips/include/asm/barrier.h b/arch/mips/include/asm/barrier.h >> index 49ff172..24c3f2c 100644 >> --- a/arch/mips/include/asm/barrier.h >> +++ b/arch/mips/include/asm/barrier.h >> @@ -113,6 +113,15 @@ static inline void wmb(void) >> ".set arch=octeon\n\t" \ >> "syncw\n\t" \ >> ".set pop" : : : "memory") >> + >> +#define __smp_store_release(p, v) \ >> +do { \ >> + compiletime_assert_atomic_type(*p); \ >> + __smp_wmb(); \ >> + __smp_rmb(); \ >> + WRITE_ONCE(*p, v); \ >> +} while (0) > This is wrong in general since smp_rmb() will only provide order between > two loads and smp_store_release() is a store. > > If this is correct for all MIPS, this needs a giant comment on exactly > how that smp_rmb() makes sense here. ... the macro is provided for Octeon only, and __smp_rmb() is actually a NOP there, but I thought to "document" the flow of thoughts from the discussion above by including it anyway. -- Best regards, Alexander Sverdlin.