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Thu, 28 Jan 2021 07:30:01 +0000 Subject: Re: [PATCH 3/6] MIPS: Octeon: qspinlock: Flush write buffer 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> <20210127203627.47510-4-alexander.sverdlin@nokia.com> From: Alexander Sverdlin Message-ID: Date: Thu, 28 Jan 2021 08:29:57 +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: AM0PR10CA0021.EURPRD10.PROD.OUTLOOK.COM (2603:10a6:208:17c::31) 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 AM0PR10CA0021.EURPRD10.PROD.OUTLOOK.COM (2603:10a6:208:17c::31) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3805.17 via Frontend Transport; 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On 27/01/2021 23:34, Peter Zijlstra wrote: > On Wed, Jan 27, 2021 at 09:36:24PM +0100, Alexander A Sverdlin wrote: >> From: Alexander Sverdlin >> >> Flushing the write buffer brings aroung 10% performace on the tight >> uncontended spinlock loops on Octeon. Refer to commit 500c2e1fdbcc >> ("MIPS: Optimize spinlocks."). > No objection to the patch, but I don't find the above referenced commit > to be enlightening wrt nudge_writes(). The best it has to offer is the > comment that's already in the code. My point was that original MIPS spinlocks had this write-buffer-flush and it got lost on the conversion to qspinlocks. The referenced commit just allows to see the last MIPS-specific implementation before deletion. >> Signed-off-by: Alexander Sverdlin >> --- >> arch/mips/include/asm/spinlock.h | 3 +++ >> 1 file changed, 3 insertions(+) >> >> diff --git a/arch/mips/include/asm/spinlock.h b/arch/mips/include/asm/spinlock.h >> index 8a88eb2..0a707f3 100644 >> --- a/arch/mips/include/asm/spinlock.h >> +++ b/arch/mips/include/asm/spinlock.h >> @@ -24,6 +24,9 @@ static inline void queued_spin_unlock(struct qspinlock *lock) >> /* This could be optimised with ARCH_HAS_MMIOWB */ >> mmiowb(); >> smp_store_release(&lock->locked, 0); >> +#ifdef CONFIG_CPU_CAVIUM_OCTEON >> + nudge_writes(); >> +#endif >> } >> >> #include -- Best regards, Alexander Sverdlin.