From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 7 May 2019 01:53:35 -0500 (CDT) From: Per Oberg Message-ID: <1907767262.9872848.1557212015078.JavaMail.zimbra@wolfram.com> In-Reply-To: <4c39d8ca-3c98-4b35-6b06-2013dc80134b@xenomai.org> References: <1823257552.1557117297954.94.KebiMail.daeyoungsong@cnu.ac.kr> <4c39d8ca-3c98-4b35-6b06-2013dc80134b@xenomai.org> Subject: Re: Xenomai Mercury and PREEMPT_RT MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable List-Id: Discussions about the Xenomai project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Philippe Gerum Cc: =?utf-8?B?7Iah64yA7JiB?= , xenomai ----- Den 6 maj 2019, p=C3=A5 kl 10:07, xenomai xenomai@xenomai.org skrev: > On 5/6/19 6:34 AM, =EC=86=A1=EB=8C=80=EC=98=81 via Xenomai wrote: > > [webmailreconf.public.do?24538165] > > Hello, expert. > > I have a question about Xenomai Mercury and PREEMPT_RT. > > Following "Xenomai 3 =E2=80=93 An Overview of the Real-Time Framework f= or > > Linux", Mercury is based on PREEMPT_RT and only offers API emulation. > > Is Mercury's latency performance better than PREEMPT_RT? > No, it merely uses what native preemption provides for. So, just to be clear. Are you saying that it should be "Just as good" as PR= EEMPT.RT when the kernel is fully patched? (Whatever that means...) Now, I don't want to start a flame-war here, that would be stupid. But I re= ally want to know your opinion on this (see for eaxmple claims made in [1])= . May we assume that the Mercury performance would be quite close to Cobolt= performance ? And how about communication with hardware communication in a PREEMT_RT setu= p? Without special RT-drivers what can we expect? For me it's not about wh= en something can be computed but rather when it can be commuicated. [1] http://linuxgizmos.com/real-time-linux-explained/ Qute: "While Xenomai performed better on most tests, and offered far less j= itter, the differences were not as great as the 300 to 400 percent latency = superiority claimed by some Xenomai boosters, said Altenberg. When tests we= re performed on userspace tasks =E2=80=94 which Altenberg says is the most = real-world, and therefore the most important, test =E2=80=94 the worst-case= reaction was about 90 to 95 microseconds for both Xenomai and RTL/PREEMPT.= RT, he claimed." > -- > Philippe. Per =C3=96berg=20