December 2012 - kernelnewbies@kernelnewbies.org

Regarding testing of OS Development specific Code
by supratim chakraborty Dec. 12, 2012

Dec. 12, 2012

I searched on the internet for an apt answer but i couldn't find one so i thought this could be a newbie-friendly place to shoot the doubt I have developed an interest in OS development (kernel) and have successfully built/compiled/configured the kernel source but i would like to know as to how do OS developers test their code ,as in- it could be really painful to make some changes to the code and then again recompile the entire kernel , make a new image and then boot from that in essence it would require - 1. Making changes 2. Compiling 3. Reflashing the kernel 4. Rebooting the machine (physical or virtual as the case may be) So I am pretty sure that this is not the way the work's done , so can i have the needed enlightenment as to how do OS developers go about making hacks /changes to the code and then testing the new build Regards Supratim Chakraborty about.me/borax12

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inconsistency of get_wchan in x86_32 and x86_64
by microstone Dec. 12, 2012

Dec. 12, 2012

Hi guys, While I was reading the code of get_wchan() in x86 32bit and 64bit, I notice the following difference, 32bit get_wchan #define top_esp (THREAD_SIZE - sizeof(unsigned long)) #define top_ebp (THREAD_SIZE - 2*sizeof(unsigned long)) unsigned long get_wchan(struct task_struct *p) { ... if (!stack_page || sp < stack_page || sp > top_esp+stack_page) return 0; bp = *(unsigned long *) sp; do { * if (bp < stack_page || bp > top_ebp+stack_page)* return 0; ... } while (count++ < 16); return 0; } 64bit get_wchan unsigned long get_wchan(struct task_struct *p) { ... if (p->thread.sp < stack || p->thread.sp >= stack+THREAD_SIZE) return 0; fp = *(u64 *)(p->thread.sp); do { * if (fp < (unsigned long)stack ||* * fp >= (unsigned long)stack+THREAD_SIZE)* return 0; ... } while (count++ < 16); return 0; } Question 1: Could anyone help tell me why in 64 bit, we don't use fp > (THREAD_SIZE - 2*sizeof(unsigned long)) like 32 bit? Question 2: Why is the limited count of frame loops 16? Thanks, Ye -- We Make every day party day

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Re: Speed Analysis Util.
by Gustavo da Silva Dec. 11, 2012

Dec. 11, 2012

I would like to tell myself: Ok, so, in 1second, my computer can access 2.000 memory cells (relatively, because there is the "inc" instruction time spent, for counting). I'm using a AMD Athlon 64 X2 L310 (1.2ghz). It would not be a easy task (for me) to develop, because I'm not a Assembly profissional programmer, and I'm not a young man who have much time to develop all utils those I would like to create. It would not be easy, too, because it will be necessary (I think/believe) to set paging (x86) mechanism, enabling long mode, ... ...Well, if not, it will be easier. I'm imaginating a very simple program!! But if someone wants to create (doesn't want to wait me), ... my tip is: "So my Friend: Let's go! Do it!"! Regards. Peace out. 2012/12/11 Lukáš Oliva <olivalukas(a)gmail.com> > Just for my curiosity, how do you plan to use the results? Also, > which processors do you intend to test (NUMA too)? > > Lukas > > 2012/12/10 Gustavo da Silva <gustavodasilva(a)gmail.com>: > > Very interesting!! Both the link and the movntq instruction. I'll read > and > > study. > > > > Thanks Tobias!! > > > > 2012/12/8 Tobias Boege <tobias(a)gambas-buch.de> > >> > >> On Sat, 08 Dec 2012, Gustavo da Silva wrote: > >> > Hello Kernel Brothers!! How are you??? > >> > > >> > So, I would like test the performance of my notebook, developing one > or > >> > two > >> > utilities, and have a better > >> > mensurement about the speed. > >> > > >> > But it can help all of us. > >> > > >> > 1st: I would like mensure the speed making a counter (exacly bogomips? > >> > may > >> > be). Loop+counter during 1 tickrate. > >> > 2nd: The most interesting: How many memory cells in ram can we > >> > access during 1tickrate? How could we develop this?! > >> > > >> > Both utils may run in long mode (64bits). Well, in real mode too; so, > we > >> > can compare the speed in the two modes! > >> > > >> > Some one knows how to develop a very small program/routine about > that?! > >> > > >> > For the 2nd situation, a simple idea wrote in codesnipet form > (consider > >> > the > >> > intention, not the sintax! there are bugs! I know. Intel syntax.) > >> > >> Obviously! ;-) > >> > >> > > >> > dw the_counter_cell 0 > >> > lea bx, the_counter_cell > >> > xor bx,bx > >> > label: > >> > inc [bx] # Could not be so simple like this, because the address > >> > can > >> > be cached. Right? > >> > loop label # breaked by an interruption. Just to express the > >> > intention. > >> > > >> > How could we create a small code for the 2nd situation, tring to force > >> > the > >> > processor to not use the cache? > >> > >> As Drepper says[0], use the movntq instruction on x86_64 to bypass the > >> cache. > >> > >> Regards, > >> Tobi > >> > >> [0] http://www.akkadia.org/drepper/cpumemory.pdf p. 47ff. > >> > >> > >> _______________________________________________ > >> Kernelnewbies mailing list > >> Kernelnewbies(a)kernelnewbies.org > >> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > > > > > > > > > > -- > > Atenciosamente, > > > > Gustavo da Silva > > gustavodasilva(a)gmail.com > > > > _______________________________________________ > > Kernelnewbies mailing list > > Kernelnewbies(a)kernelnewbies.org > > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > > > -- Atenciosamente, Gustavo da Silva gustavodasilva(a)gmail.com

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8250 UART doesn't populate /proc/iomem?
by Woody Wu Dec. 11, 2012

Dec. 11, 2012

Hi, list I found some io memory information is lost from /dev/iomem and want to find out why. I have a 2.6.16 kernel running on a ARM board (Samsung S3C2410). From the kernel log, I see 16 8250 serial ports were detected, and each of thoese ports has a memory address: Serial: 8250/16550 driver $Revision: 1.90 $ 16 ports, IRQ sharing enabled serial8250: tts0 at MMIO 0xe1400000 (irq = 16) is a 16550A serial8250: tts1 at MMIO 0xe1400008 (irq = 16) is a 16550A serial8250: tts2 at MMIO 0xe1400010 (irq = 17) is a 16550A serial8250: tts3 at MMIO 0xe1400018 (irq = 17) is a 16550A serial8250: tts4 at MMIO 0xe1400020 (irq = 18) is a 16550A serial8250: tts5 at MMIO 0xe1400028 (irq = 18) is a 16550A serial8250: tts6 at MMIO 0xe1400030 (irq = 19) is a 16550A serial8250: tts7 at MMIO 0xe1400038 (irq = 19) is a 16550A serial8250: tts8 at MMIO 0xe1400040 (irq = 48) is a 16550A serial8250: tts9 at MMIO 0xe1400048 (irq = 48) is a 16550A serial8250: tts10 at MMIO 0xe1400050 (irq = 49) is a 16550A serial8250: tts11 at MMIO 0xe1400058 (irq = 49) is a 16550A serial8250: tts12 at MMIO 0xe1400060 (irq = 60) is a 16550A serial8250: tts13 at MMIO 0xe1400068 (irq = 60) is a 16550A serial8250: tts14 at MMIO 0xe1400070 (irq = 61) is a 16550A serial8250: tts15 at MMIO 0xe1400078 (irq = 61) is a 16550A I can read/write these serial ports from /dev/ttys*, in other words, they do exist. I also can find the driver info from /proc/devices: Character devices: ... 4 /dev/vc/0 4 tty 4 tts 5 /dev/tty 5 /dev/console 5 /dev/ptmx 7 vcs ... The problem is, I don't understand why there is no information about these ports in /proc/iomem file. The 'iomem' file now contains: 11000000-11000ffe : AX88796B 19000000-19000ffe : AX88796B 30000000-33ffffff : System RAM 3001c000-301e826b : Kernel text 301ea000-302234a3 : Kernel data 49000000-490fffff : s3c2410-ohci 49000000-490fffff : ohci_hcd 4e000000-4e0fffff : s3c2410-nand 4e000000-4e0fffff : s3c2410-nand 50000000-50003fff : s3c2410-uart.0 50000000-500000ff : s3c2410-uart 50004000-50007fff : s3c2410-uart.1 50004000-500040ff : s3c2410-uart 50008000-5000bfff : s3c2410-uart.2 50008000-500080ff : s3c2410-uart 53000000-530fffff : s3c2410-wdt 54000000-540fffff : s3c2410-i2c 5a000000-5a0fffff : s3c2410-sdi 5a000000-5a0fffff : mmci-s3c2410 You see, there is no serial8250 informations. Can anyone here please tell me how this can happen? Does it mean the serial8250 driver don't populate or register in the /proc/iomem? -- woody I can't go back to yesterday - because I was a different person then.

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Speed Analysis Util.
by Gustavo da Silva Dec. 10, 2012

Dec. 10, 2012

Hello Kernel Brothers!! How are you??? So, I would like test the performance of my notebook, developing one or two utilities, and have a better mensurement about the speed. But it can help all of us. 1st: I would like mensure the speed making a counter (exacly bogomips? may be). Loop+counter during 1 tickrate. 2nd: The most interesting: How many memory cells in ram can we access during 1tickrate? How could we develop this?! Both utils may run in long mode (64bits). Well, in real mode too; so, we can compare the speed in the two modes! Some one knows how to develop a very small program/routine about that?! For the 2nd situation, a simple idea wrote in codesnipet form (consider the intention, not the sintax! there are bugs! I know. Intel syntax.) dw the_counter_cell 0 lea bx, the_counter_cell xor bx,bx label: inc [bx] # Could not be so simple like this, because the address can be cached. Right? loop label # breaked by an interruption. Just to express the intention. How could we create a small code for the 2nd situation, tring to force the processor to not use the cache? Regards. Peace out. -- Atenciosamente, Gustavo da Silva gustavodasilva(a)gmail.com

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How to config to compile ramfs?
by Bin Wang Dec. 10, 2012

Dec. 10, 2012

I want to compile the code under fs/ramfs. But when I "make fs/ramfs", it does not output anything under fs/ramfs. I don't see anything like "RAMFS=" in configure file. I'd like to know where is it? Thanks Bin Wang

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Asking another process sleep from another process or interrupt context
by Sunil Agham Dec. 10, 2012

Dec. 10, 2012

Hello List, This is what I am trying to do in linux kernel. When some event occurs; Process X wants to tell process Y to un-schedule itself(Y) [ and change state from "running or ready to run" to "not ready to run until told otherwise" ]. Process X will take care of waking up Y later. One approach probably is to set "*need_resched*" for process Y so that schedular picks another process at the first opportunity. Is there any other alternative ? Is it safe to do this from interrupt context instead of process X's context ? -- Sunil

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question about building a module
by Kevin Wilson Dec. 8, 2012

Dec. 8, 2012

Hi, I am adding some code of my own **only** under net/bluetooth in some file there. There is only exactly one module which is changed by my addition, This is net/bluetooth/bluetooth.ko Now, when I run 'make -j2 modules' it takes quite a time, even If I did one change in one line in a file under net/bluetooth. I assume that it has to do with stage 2 of the build, which says something about ... Building modules, stage 2. MODPOST 855 modules ... see below full log. Now my question is this: Is there a way to make things more efficent when building a module, on the assumption that I do not change anything anywhere except /net/bluetooth (in this case)? somehow telling the MODPOST that only one module is changes ? I remember I once saw (not sure) a suggestion to build only a specified moule like: make net/bluetooth But in this case the result is the same. any ideas? rgs Kevin myhost> make modules make[1]: Nothing to be done for `all'. make[1]: Nothing to be done for `relocs'. CHK include/generated/uapi/linux/version.h CHK include/generated/utsrelease.h CALL scripts/checksyscalls.sh CC [M] net/bluetooth/hci_sock.o LD [M] net/bluetooth/bluetooth.o Building modules, stage 2. MODPOST 855 modules CC net/bluetooth/bluetooth.mod.o LD [M] net/bluetooth/bluetooth.ko

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On loading userspace data into particular section of physical memory (ARM)
by Joel A Fernandes Dec. 8, 2012

Dec. 8, 2012

I am looking at a problem that might be too difficult to solve, or might not if I'm missing something so I thought I'd bounce it off this group, Basically I have an application in userspace who's ".data" section _has_ to be loaded into particular locations in physical memory. That is, there is a chunk of physical memory that has to contain the .data section and no other part of physical memory should. What is the easiest way to do this? I guess, changes might be required to the ELF loaders in fs/bin*.c. Any other tricks? Is it non-trivial to add a new memory zone to the kernel that manages a particular section of physical memory? I thought if a new zone could be added, then we could possibly modify the kernel ELF loader to recognize a specially marked .data section and alloc memory from that special zone when allocating page frames. Let me know if you have any ideas, Thanks, Regards, Joel

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Best and fastest way to understand kernel subsystem ?
by Shraddha Kamat Dec. 8, 2012

Dec. 8, 2012

What is the best (and the fastest ) way to understand a kernel subsystem ( for e.g., filesystem , Networking .. etc.) -- Shraddha

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