From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <53FF8DF9.9080405@xenomai.org> Date: Thu, 28 Aug 2014 22:15:53 +0200 From: Gilles Chanteperdrix MIME-Version: 1.0 References: <53FF8AC7.5090301@xenomai.org> In-Reply-To: <53FF8AC7.5090301@xenomai.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai] Low-latency desktop setting List-Id: Discussions about the Xenomai project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Yogi A. Patel" , "xenomai@xenomai.org" On 08/28/2014 10:02 PM, Gilles Chanteperdrix wrote: > On 08/28/2014 09:49 PM, Yogi A. Patel wrote: >> In configuring the kernel (after patching with xenomai), there is an >> option to change the preemption model to "low-latency desktop". >> >> Is this a setting that should be set? Or should it be left to the >> default preemption mode?? >> >> How does this setting affect the real-time performance of a xenomai >> enabled kernel? > > This option is about Linux preemption, it affects how often Linux is > willing to preempt itself, in the throughput/latency fight, it gives > advantage to (Linux) latency at the expense of througput. It does not > affect Xenomai directly, but rather indirectly: it creates a code with a > lower "density", by littering the Linux kernel execution with checks for > the need of rescheduling, so that Linux has a larger pollution effect on > caches. In my experience, you get slightly lower Linux latencies by > turning CONFIG_PREEMPT off (selecting CONFIG_PREEMPT_NONE). > I meant you get lower XENOMAI latencies by turning it off. Of course you get higher Linux latencies. -- Gilles.