February 2021 - kernelnewbies@kernelnewbies.org

Re: Scheduler benchmarks
by Muni Sekhar April 29, 2021

April 29, 2021

On Tue, Aug 18, 2020 at 11:45 PM peter enderborg <peter.enderborg(a)sony.com> wrote: > > On 8/18/20 7:53 PM, Muni Sekhar wrote: > > On Tue, Aug 18, 2020 at 11:06 PM Greg KH <greg(a)kroah.com> wrote: > >> On Tue, Aug 18, 2020 at 11:01:35PM +0530, Muni Sekhar wrote: > >>> On Tue, Aug 18, 2020 at 10:44 PM Greg KH <greg(a)kroah.com> wrote: > >>>> On Tue, Aug 18, 2020 at 10:24:13PM +0530, Muni Sekhar wrote: > >>>>> On Tue, Aug 18, 2020 at 8:06 PM Greg KH <greg(a)kroah.com> wrote: > >>>>>> On Tue, Aug 18, 2020 at 08:00:11PM +0530, Muni Sekhar wrote: > >>>>>>> Hi all, > >>>>>>> > >>>>>>> I’ve two identical Linux systems with only kernel differences. > >>>>>> What are the differences in the kernels? > >>>> You didn't answer this question, is this the same kernel source being > >>>> compared here? Same version? Same compiler? Everything identical? > >>> Both systems are having exactly the same hardware configuration. > >>> Compiler and kernel versions are different. One system has Ubuntu > >>> 16.04.4 LTS(4.4.0-66-generic kernel with gcc version 5.4.0) kernel and > >>> the other one has Ubuntu 18.04.4 LTS(4.15.0-91-generic kernel with gcc > >>> version 7.5.0). > >> Those are _very_ different kernel versions, with many years and tens of > >> thousands of different changes between them. > >> > >> Hopefully the newer kernel is faster, so just stick with that :) > > But unfortunately the newer kernel is very slow, that is the reason > > for starting this investigation :) > > Any type of help, and guidelines to dive deeper will be highly appreciated. > > On the 4.4 kernel you dont have > > +CONFIG_RETPOLINE=y > +CONFIG_INTEL_RDT=y Thanks! That is helpful. Yes, I see 4.4 kernel don't have the above two config options. What analysis can be done to narrow down the root cause? Any example of reference could be helpful to understand. > > And your base is very different two. > > Try to use mainline on both system and see. > > You can also use the same base kernel version from ubuntu and > > run your test. > > > >> greg k-h > > > > > -- Thanks, Sekhar

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are 1-wire devices "discoverable"?
by Trevor Woerner March 19, 2021

March 19, 2021

Hi, I just watched the amazing device tree presentation recently done by Thomas Petazzoni (from Bootlin) for ST[1]. During the presentation, which is amazing, by the way ;-), Thomas describes the 1-wire protocol as not being discoverable. I was recently playing with the DS18B20 temperature sensor, which uses the 1-wire bus.[2] In fact, I was playing with a bunch of different temperature sensors with a RaspberryPi, and then gave a talk at a local RaspberryPi Meetup group that I regularly attend.[3] My only experience with the 1-wire bus is with this one device, so maybe the details of how the DS18B20 work are specific to the DS18B20 and not the way 1-wire devices work in general? But my (humble) conclusion is that the 1-wire bus is discoverable (or at least quasi-discoverable). It's true that you do need a device tree overlay to tell the kernel that you want to use the 1-wire bus, and you have to tell the kernel which GPIO pin you want to use as the 1 wire, but after that, attaching DS18B20 devices to a running system works quite magically.[4] Each DS18B20 has a unique 64-bit number burned into it, the first 8 bits specify the device type (i.e. the DS18B20), the next 48 bits are a unique serial number, and the last 8 bits are a CRC of the previous 56 bits. Due to the inclusion of the 8-bit device type, when I plug a DS18B20 into my board, the kernel automatically creates a sysfs entry for it with a "temperature" file that I can read to obtain the temperature in Celcius. I don't know if that qualifies as "discoverable"? It's certainly a lot more discoverable than I2C or SPI, although maybe not quite as discoverable as, say, PCI. Specifying the 1 wire is not discoverable, but plugging 1-wire devices into my board is maybe something that could be described as discoverable? Best regards, Trevor [1] https://www.youtube.com/watch?v=a9CZ1Uk3OYQ [2] https://twoerner.blogspot.com/2020/12/temperature-readings-with-ds18b20-and… [3] https://twoerner.blogspot.com/2021/01/sensing-temperature-with-raspberrypi.… [4] https://twoerner.blogspot.com/2020/12/multiple-ds18b20-temperature-probes.h…

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Fwd: Re: [GIT PULL] PCI changes for v5.12
by wuzhouhui Feb. 26, 2021

Feb. 26, 2021

I'm confused about what the Linus said. It seemed that the branch cannot be rebased after merged into linux-next under normal circumstances, why? Linus found this issue by check commit time of commits, but I also found so many commit in mainline are too young to be merged into linux-next before merge to mainline. If the rebase is not recommended, why people like to do rebase after commits are merged into linux-next? Thanks -------- Forwarded Message -------- Subject: Re: [GIT PULL] PCI changes for v5.12 Date: Wed, 24 Feb 2021 11:21:44 -0800 From: Linus Torvalds <torvalds(a)linux-foundation.org> To: Bjorn Helgaas <helgaas(a)kernel.org> CC: Linux PCI <linux-pci(a)vger.kernel.org>, Linux Kernel Mailing List <linux-kernel(a)vger.kernel.org>, Lorenzo Pieralisi <lorenzo.pieralisi(a)arm.com> On Wed, Feb 24, 2021 at 11:03 AM Bjorn Helgaas <helgaas(a)kernel.org> wrote: > git://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci.git tags/pci-v5.12-changes I pulled this, but I'm now unpulling it again. Why are many of those commits only two hours old, and most of the rest is from yesterday? Has any of this been in linux-next? And if it has, then why was it rebased, and why didn't you explain *why* it was rebased if so? I'm willing to pull this if it turns out it _has_ been in linux-next, but I need explanations. Linus

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How to make .dtb from .dts file (how to set include path for #include .. ?)
by ckim＠etri.re.kr Feb. 24, 2021

Feb. 24, 2021

Hello all, In linux kernel source, there are many .dts files (device tree source) For example there is a file ./arch/arm64/boot/dts/arm/juno.dts. To tried to make juno.dtb from juno.dts but I don't know how to do it. (by the way, once I did make for the kernel build, junno.dtb file seems to be generated in the same directory) Just in case I want to make my own .dts and .dtb, I tried compling juno.dts file. (I had installed dtc on my ubuntu 16.04 machine before) $ dtc -I dts -O dtb -o juno.dtb arch/arm64/boot/dts/arm/juno.dts Error: arch/arm64/boot/dts/arm/juno.dts:11.1-9 syntax error FATAL ERROR: Unable to parse input tree The dtc program cannot process the line below in the .dts file.(line 11) #include <dt-bindings/interrupt-controller/arm-gic.h> I don't know how I should let the preprocessing kick in. I tried (because there is include/dt-bindings/interrupt-controller/arm-gic.h) $ dtc -i include -I dts -O dtb -o juno.dtb arch/arm64/boot/dts/arm/juno.dts But it doesn't work. How can I use dtc program to make juno.dtb? Or if I have to use Makefile, what is the command? Thanks, Chan Kim

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Eudyptula task 6
by Jules Irenge Feb. 24, 2021

Feb. 24, 2021

Hi guys I am currently stuck at task 6 haha because of error checking on return for simple_write_buffer I have researched on it but I just can't get appropriate documentation on error code return of the wrapper especially when the return is negative, I will appreciate if someone points me to some interesting ressource on the matter -- Jules *..*

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Enable 9bit-mode in a serial device
by Jorge Fernandez Monteagudo Feb. 22, 2021

Feb. 22, 2021

Hi all, I'm wondering what's the best way to enable the 9bit-mode for a given tty serial device. I have a motherboard with a NCT6102D Nuvoton super IO with 6 UARTs. This device is supported by the 8250/16550 driver already in kernel and I'm able to communicate two serial port with a NULL modem cable. >From NCT6102D Nuvoton datasheet it seems some bits has to be set in order to enable this mode to use the parity bit as the 9 bit. Any hint? Any driver from drivers/tty/serial/8250 can be used as a guide? Some user space code can be used to get access to registers? Thanks, Jorge

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Does 'make oldconfig' work across different architectures?
by ckim＠etri.re.kr Feb. 19, 2021

Feb. 19, 2021

Hello folks, When we want to use an old .config file for a new kernel build, we can use (place in build location) that .config and do 'make oldconfig' so that the build system lets us to fill the new config variables. I'm curious if this 'make oldconfig' will work if the old .config is from different architecture (like sparc) and I have to configure it for aarch64. The old .config file is a minimal configuration with timer, interrupt controller and uart for minimal linux booting. Thanks! Chan Kim

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Is it possible to disable NEON to cause a trap with NEON code?
by Jeffrey Walton Feb. 12, 2021

Feb. 12, 2021

Hi Everyone, I'm trying to setup a test case on ARM A-32. I want to ensure a NEON code path is properly guarded at runtime. I'd like to disable NEON at boot time so that a SIGILL is raised for NEON instructions. If I get a SIGILL, it tells me there's some NEON in non-guarded paths. Is it possible to disable NEON at boot time? Thanks in advance. Jeff

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Enquiry
by Abhijit Paul Feb. 10, 2021

Feb. 10, 2021

Hello, I am new to kernel development. As a beginner, I don't know which part I will work on. Can anyone suggest me what I do as a beginner? Best, Abhijit

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Changelog of features / drivers removed from kernel?
by Evan T Mesterhazy Feb. 9, 2021

Feb. 9, 2021

Apologies if this comes off as a lazy question, but after a fair bit of searching I've been unable to find a changelog indicating which device drivers / features were dropped from various versions of the kernel. Does such a changelog exist? I'm specifically trying to narrow down why the PCI devices on a server I have work with 5.8 and don't work with 5.9+. The server is circa 2014, so I suppose there's an off chance support for some component got dropped. Thanks in advance, Evan -- Evan Mesterhazy etm2131(a)columbia.edu

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