From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <53539207.2030803@xenomai.org> Date: Sun, 20 Apr 2014 11:23:19 +0200 From: Gilles Chanteperdrix MIME-Version: 1.0 References: <7dad12a6.21b0a.14574613527.Coremail.ericvic@163.com> <535110C3.40500@xenomai.org> <59ece04.26b88.1457d86db18.Coremail.ericvic@163.com> <53538D60.8040107@xenomai.org> In-Reply-To: <53538D60.8040107@xenomai.org> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit Subject: Re: [Xenomai] imx6q xenomai ipipe-3.0-imx6q List-Id: Discussions about the Xenomai project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: eric Cc: huang.c.h@lynuc.cn, liu.h.f@lynuc.cn, "xenomai@xenomai.org" Le 20/04/2014 11:03, Gilles Chanteperdrix a écrit : > Le 20/04/2014 07:06, eric a écrit : >> So if my program use lots of memory operations for a long time it maybe >> gives non real-time activities opportunity to thrash the cache? > > It is unrelated, but on a multi-core processor even when one core is > running a real-time task, other cores can thrash the cache at will, or > slow down the real-time task by using a shared ressource (for instance > DDR) and starving the core where the real-time task runs. By default the > L2 cache is shared between all cores, you can try and reserve parts of > the cache for each core (check the l2x0 registers documentation to see > how), I tried this on omap4, but it results on worse latencies, > situation may be different on imx6 though. Another problem is that since > the L1 cache is per-core, I believe, and we disable L2 write allocate, > reading on one core memory written on another core results in accesses > at the DDR speed, and not at the cache speed. > > All this to say that Xenomai focuses on trying to schedule your driver > interrupts and application threads in a deterministic fashion but it is > your job to make sure that these interrupts and threads do not take too > long a time to execute, because if they do, yes, your application will > not meet its deadlines, but it is not Xenomai's fault. I do not mean to say that you do not have a problem with Xenomai on imx6q, but so far, I have not understood what this problem was. -- Gilles.