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Fri, 30 Nov 2018 02:25:45 +0000 From: Honnappa Nagarahalli To: "Van Haaren, Harry" , Stephen Hemminger CC: "dev@dpdk.org" , nd , Dharmik Thakkar , Malvika Gupta , "Gavin Hu (Arm Technology China)" , nd Thread-Topic: [dpdk-dev] [RFC 0/3] tqs: add thread quiescent state library Thread-Index: AQHUhqB8tEevwcHR9UqXBYKYUzkOUKVkOZ6AgANeouA= Date: Fri, 30 Nov 2018 02:25:45 +0000 Message-ID: References: <20181122033055.3431-1-honnappa.nagarahalli@arm.com> <20181127142803.423c9b00@xeon-e3> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: spf=none (sender IP is ) smtp.mailfrom=Honnappa.Nagarahalli@arm.com; x-originating-ip: [217.140.111.135] x-ms-publictraffictype: Email x-microsoft-exchange-diagnostics: 1; AM6PR08MB3846; 6:GKfrk6LymjjjQihW3/SC+Eg3L2DqdYS1TjjGGwU3Y/PwB+pjkczz2aIBjqgCXL4NvHqtGBEHf93tivyebG7YvyTmRsXRxocjtqgj07yNpBXiF/zsW9HfbCFF+qLDWnBz9AYA4H/xz9NfizLMJLocHloAyrq5z68GHLvYOO8nkW7ANGWT95ysiCeyJnMNocR87sggAMvBApQhmdhI1Br1JdLW24X/7XCf5QsdNKPcbTHsXk52HfUfqWBz2Hhip/RONYg70+PL/0AJjk6r5ZY17t/wPhdLSVd1fLGnwpsfg0OF5yb9ODmnOq9qkRWkwkTgAWHVbXYpkC848lTIQhBvoUk/Z1FweFO4ZyqnGOg9sbq8LJXfA+JCAs6UUEx1MAYmEgrMvqJMQijZKrFroFfS2J03YcI3Zf8FJIhMlmB3vkrHILQ24lo3qEuRv/MLdZLKMo/y7bJ45Hf1UqC6B1fLfg==; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-Network-Message-Id: bbc7b66b-e7e0-472f-56f1-08d6566b2240 X-MS-Exchange-CrossTenant-originalarrivaltime: 30 Nov 2018 02:25:45.4697 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM6PR08MB3846 Subject: Re: [dpdk-dev] [RFC 0/3] tqs: add thread quiescent state library X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 30 Nov 2018 02:25:47 -0000 > > > > > > > Mixed feelings about this one. > > > > Love to see RCU used for more things since it is much better than > > reader/writer locks for many applications. But hate to see DPDK > > reinventing every other library and not reusing code. Userspace RCU > > https://liburcu.org/ is widely supported by distro's, more throughly > > tested and documented, and more flexiple. > > > > The issue with many of these reinventions is a tradeoff of DPDK > > growing another dependency on external library versus using common code= . > > > > For RCU, the big issue for me is the testing and documentation of how > > to do RCU safely. Many people get it wrong! >=20 >=20 > Some notes on liburcu (and my amateur understanding of LGPL, I'm not a > license lawyer :) >=20 > Liburcu is LGPL, which AFAIK means we must dynamically link applications = if > the application code is BSD or other permissive licenses. >=20 > The side effect of this is that urcu function calls must be "real" functi= on calls > and inlining them is not possible. Therefore using liburcu in LGPL mode c= ould > have a performance impact in this case. I expect estimating the performan= ce > cost would be > difficult as its pretty much a case-by-case depending on what you're doin= g in > the surrounding code. >=20 > Generally I'm in favour of using established libraries (particularly for = complex > functionality like RCU) but in this case I think there's a tradeoff with = raw > performance. The licensing info [1] is very interesting. Again I am no lawyer :) [1] https://github.com/urcu/userspace-rcu/blob/master/include/urcu/static/u= rcu-qsbr.h#L184