From mboxrd@z Thu Jan 1 00:00:00 1970 References: <20160602082318.GB1801@hermes.click-hack.org> <5755204C.6090701@sigmatek.at> <20160606153545.GA376@hermes.click-hack.org> <5756D673.4080408@sigmatek.at> <20160607170050.GA13922@hermes.click-hack.org> <57714C60.4070407@sigmatek.at> <20160627164604.GH18662@hermes.click-hack.org> <577235C4.2080507@sigmatek.at> <20160628083404.GI18662@hermes.click-hack.org> <57724022.8010904@sigmatek.at> <20160628091747.GK18662@hermes.click-hack.org> From: Wolfgang Netbal Message-ID: <57724333.6010608@sigmatek.at> Date: Tue, 28 Jun 2016 11:28:19 +0200 MIME-Version: 1.0 In-Reply-To: <20160628091747.GK18662@hermes.click-hack.org> Content-Type: text/plain; charset="windows-1252"; format="flowed" Content-Transfer-Encoding: quoted-printable Subject: Re: [Xenomai] Performance impact after switching from 2.6.2.1 to 2.6.4 Reply-To: wolfgang.netbal@sigmatek.at List-Id: Discussions about the Xenomai project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: gilles.chanteperdrix@xenomai.org Cc: xenomai@xenomai.org Am 2016-06-28 um 11:17 schrieb Gilles Chanteperdrix: > On Tue, Jun 28, 2016 at 11:15:14AM +0200, Wolfgang Netbal wrote: >> >> Am 2016-06-28 um 10:34 schrieb Gilles Chanteperdrix: >>> On Tue, Jun 28, 2016 at 10:31:00AM +0200, Wolfgang Netbal wrote: >>>> Am 2016-06-27 um 18:46 schrieb Gilles Chanteperdrix: >>>>> On Mon, Jun 27, 2016 at 05:55:12PM +0200, Wolfgang Netbal wrote: >>>>>> Am 2016-06-07 um 19:00 schrieb Gilles Chanteperdrix: >>>>>>> On Tue, Jun 07, 2016 at 04:13:07PM +0200, Wolfgang Netbal wrote: >>>>>>>> Am 2016-06-06 um 17:35 schrieb Gilles Chanteperdrix: >>>>>>>>> On Mon, Jun 06, 2016 at 09:03:40AM +0200, Wolfgang Netbal wrote: >>>>>>>>>> Am 2016-06-02 um 10:23 schrieb Gilles Chanteperdrix: >>>>>>>>>>> On Thu, Jun 02, 2016 at 10:15:41AM +0200, Wolfgang Netbal wrote: >>>>>>>>>>>> Am 2016-06-01 um 16:12 schrieb Gilles Chanteperdrix: >>>>>>>>>>>>> On Wed, Jun 01, 2016 at 03:52:06PM +0200, Wolfgang Netbal wro= te: >>>>>>>>>>>>>> Am 2016-05-31 um 16:16 schrieb Gilles Chanteperdrix: >>>>>>>>>>>>>>> On Tue, May 31, 2016 at 04:09:07PM +0200, Wolfgang Netbal w= rote: >>>>>>>>>>>>>>>> Dear all, >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> we have moved our application from "XENOMAI 2.6.2.1 + Linu= x 3.0.43" to >>>>>>>>>>>>>>>> "XENOMAI 2.6.4. + Linux 3.10.53". Our target is an i.MX6DL= . The system >>>>>>>>>>>>>>>> is now up and running and works stable. Unfortunately we s= ee a >>>>>>>>>>>>>>>> difference in the performance. Our old combination (XENOMA= I 2.6.2.1 + >>>>>>>>>>>>>>>> Linux 3.0.43) was slightly faster. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> At the moment it looks like that XENOMAI 2.6.4 calls >>>>>>>>>>>>>>>> xnpod_schedule_handler much more often then XENOMAI 2.6.2.= 1 in our old >>>>>>>>>>>>>>>> system. Every call of xnpod_schedule_handler interrupts o= ur main >>>>>>>>>>>>>>>> XENOMAI task with priority =3D 95. >>>>>>>> As I wrote above, I get interrupts 1037 handled by rthal_apc_handl= er() >>>>>>>> and 1038 handled by xnpod_schedule_handler() while my realtime task >>>>>>>> is running on kernel 3.10.53 with Xenomai 2.6.4. >>>>>>>> On kernel 3.0.43 with Xenomai 2.6.4 there are no interrupts, excep= t the >>>>>>>> once that are send by my board using GPIOs, but this virtual inter= rupts >>>>>>>> are assigned to Xenomai and Linux as well but I didn't see a handl= er >>>>>>>> installed. >>>>>>>> I'm pretty sure that these interrupts are slowing down my system, = but >>>>>>>> where do they come from ? >>>>>>>> why didn't I see them on Kernel 3.0.43 with Xenomai 2.6.4 ? >>>>>>>> how long do they need to process ? >>>>>>> How do you mean you do not see them? If you are talking about the >>>>>>> rescheduling API, it used no to be bound to a virq (so, it would >>>>>>> have a different irq number on cortex A9, something between 0 and 31 >>>>>>> that would not show in the usual /proc files), I wonder if 3.0 is >>>>>>> before or after that. You do not see them in /proc, or you see them >>>>>>> and their count does not increase? >>>>>> Sorry for the long delay, we ran a lot of tests to find out what cou= ld >>>>>> be the reason for >>>>>> the performance difference. >>>>>> >>>>>> If I call cat /proc/ipipe/Xenomai I dont see the IRQ handler assigne= d to >>>>>> the virtual >>>>>> IRQ on Kernel 3.0.43, but it looks like thats an issue of the Kernel >>>>>>> As for where they come from, this is not a mystery, the reschedule >>>>>>> IPI is triggered when code on one cpu changes the scheduler state >>>>>>> (wakes up a thread for instance) on another cpu. If you want to >>>>>>> avoid it, do not do that. That means, do not share mutex between >>>>>>> threads running on different cpus, pay attention for timers to be >>>>>>> running on the same cpu as the thread they signal, etc... >>>>>>> >>>>>>> The APC virq is used to multiplex several services, which you can >>>>>>> find by grepping the sources for rthal_apc_alloc: >>>>>>> ./ksrc/skins/posix/apc.c: pse51_lostage_apc =3D rthal_apc_all= oc("pse51_lostage_handler", >>>>>>> ./ksrc/skins/rtdm/device.c: rtdm_apc =3D rthal_apc_alloc("defer= red RTDM close", rtdm_apc_handler, >>>>>>> ./ksrc/nucleus/registry.c: rthal_apc_alloc("registry_expor= t", ®istry_proc_schedule, NULL); >>>>>>> ./ksrc/nucleus/pipe.c: rthal_apc_alloc("pipe_wakeup", &xnpipe_= wakeup_proc, NULL); >>>>>>> ./ksrc/nucleus/shadow.c: rthal_apc_alloc("lostage_handle= r", &lostage_handler, NULL); >>>>>>> ./ksrc/nucleus/select.c: xnselect_apc =3D rthal_apc_alloc("x= nselectors_destroy", >>>>>>> >>>>>>> It would be interesting to know which of these services is triggered >>>>>>> a lot. One possibility I see would be root thread priority >>>>>>> inheritance, so it would be caused by mode switches. This brings the >>>>>>> question: do your application have threads migrating between primary >>>>>>> and secondary mode, do you see the count of mode switches increase >>>>>>> with the kernel changes, do you have root thread priority >>>>>>> inheritance enabled? >>>>>>> >>>>>> Here a short sum up of our tests and the results and at the end a few >>>>>> questions :-) >>>>>> >>>>>> we are using a Freescale imx6dl on our hardware and upgraded our ope= rating system from >>>>>> Freescale Kernel 3.0.43 with Xenomai 2.6.2.1 and U-Boot 2013.04 as c= ompiler we use GCC 4.7.2 >>>>>> Freescale Kernel 3.10.53 with Xenomai 2.6.4 and U-Boot 2016.01 as co= mpiler we use GCC 4.8.2 >>>>>> On both Kernels the CONFIG_SMP is set. >>>>>> >>>>>> What we see is that when we running a customer project in a Xenomai = task with priority 95 >>>>>> tooks 40% of the CPU time on Kernel 3.0.43 >>>>>> and 47% of CPU time on Kernel 3.10.53 >>>>>> >>>>>> so the new system is slower by 7% if we sum up this to 100% CPU load= we have a difference of 15% >>>>>> To find out what is the reason for this difference we ran the follow= ing test. >>>>>> We tried to get the new system faster by change some components of t= he system. >>>>>> >>>>>> -Changing U-Boot on new system -> still 7% slower >>>>>> -Copy Kernel 3.0.43 to new system -> still 7% slower >>>>>> -Creating Kernel 3.0.43 with >>>>>> Xenomai 2.6.4 and copy it to new system -> still 7% slower >>>>>> -Compiling the new system with >>>>>> old GCC version -> st= ill 7% slower >>>>>> -We also checked the settings for RAM and CPU clock -> these are equ= al >>>>>> >>>>>> It looks like that is not one of the big components, >>>>>> so we started to test some special functions like rt_timer_tsc() >>>>>> In the following example we stay for 800=B5s in the while loop and >>>>>> start this loop again after 200=B5s delay. >>>>>> The task application running this code has priotity 95. >>>>>> >>>>>> Here a simplified code snipped >>>>>> start =3D rt_timer_tsc(); >>>>>> do >>>>>> { >>>>>> current =3D rt_timer_tsc(); >>>>>> i++;=09 >>>>>> } while((current - start) < 800) >>>>> If your CPU is running at 1 GHz and uses the global timer as clock >>>>> source, the clock source runs at 500 MHz, so 800 ticks of the tsc is >>>>> something around 1.6 us >>>> Sorry I simplified the code snippet a little bit to much. >>>> Thats the correct code. >>>> >>>> current =3D rt_timer_tsc2ns(rt_timer_tsc()); >>>> >>>>> So, I do not really understand what you are talking about. But are >>>>> you sure the two kernels use the same clocksource for xenomai? >>>>> >>>>> Could you show us the result of "dmesg | grep I-pipe" with the two >>>>> kernels ? >>>> Output of Kernel 3.10.53 with Xenomai 2.6.4 >>>> I-pipe, 3.000 MHz clocksource >>>> I-pipe, 396.000 MHz clocksource >>>> I-pipe, 396.000 MHz timer >>>> I-pipe, 396.000 MHz timer >>>> I-pipe: head domain Xenomai registered. >>>> >>>> Output of Kernel 3.0.43 with Xenomai 2.6.2.1 >>>> [ 0.000000] I-pipe 1.18-13: pipeline enabled. >>>> [ 0.331999] I-pipe, 396.000 MHz timer >>>> [ 0.335720] I-pipe, 396.000 MHz clocksource >>>> [ 0.844016] I-pipe: Domain Xenomai registered. >>>> >>>> The controller is a imx6dl, this controller can run maximum 800MHz >>> Ok, so the new kernel registers two tsc emulations, could you run >>> the "tsc" regression test to measure the tsc latency? The two tsc >>> emulations have very different latencies, so the result would be >>> unmistakable. >>> >> Output of Kernel 3.10.53 with Xenomai 2.6.4 >> /usr/xenomai/bin/latency > This test is named "latency", not "tsc". As the different names > imply, they are not measuring the same thing. > Sorry for the stupied question, but where do I find the "tsc" test, because in folder /usr/xenomai/bin/=20 is it not located