January 2016 - kernelnewbies@kernelnewbies.org

'bin/sh: can't access tty' when boot from kernel-4.3.3
by Hao Lee Jan. 25, 2016

Jan. 25, 2016

Hi, I encounter a problem when I boot from kernel-4.3.3. I use 'make allnoconfig' to generate an initial config file and use 'make menuconfig' to configure my kernel then compile it. But when I try to boot from my new kernel, I see a message: ' bin/sh: can't access tty; job control turned off '. I have searched some solutions on google, but I can't solve this problem. So, could someone give me some advice or some tips to solve it. Thanks!!! My development environment: CentOS 6.0 with kernel-2.6.32 gcc 4.4.7 binutils 2.20 make 3.81 Regards, Hao Lee

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Re: CFS: Scheduler: How does each change in 'nice' value result in 10% change in CPU time?
by alexander198961 Jan. 23, 2016

Jan. 23, 2016

From m2 -------- Original message -------- Sender: John Locke <jlockefree(a)gmail.com> Time: Thu 1/21 17:53 To: kernelnewbies(a)kernelnewbies.org Subject: CFS: Scheduler: How does each change in 'nice' value result in 10% change in CPU time? >Can anyone explain how the weights that the 'nice' values are mapped >to actually result in an ~10% change in CPU time as you go from one >nice level to the next? I can't make out how the comment here actually >computes: (https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/k…) > >/* > * Nice levels are multiplicative, with a gentle 10% change for every > * nice level changed. I.e. when a CPU-bound task goes from nice 0 to > * nice 1, it will get ~10% less CPU time than another CPU-bound task > * that remained on nice 0. > * > * The "10% effect" is relative and cumulative: from _any_ nice level, > * if you go up 1 level, it's -10% CPU usage, if you go down 1 level > * it's +10% CPU usage. (to achieve that we use a multiplier of 1.25. > * If a task goes up by ~10% and another task goes down by ~10% then > * the relative distance between them is ~25%.) > */ >static const int prio_to_weight[40] = { > >If I take an example of 2 tasks both with weight=1024 (NICE_0) they >should each get 50% of the CPU time. If 1 of the tasks is reniced to >NICE_1 then the NICE_0 task will get 1024/(1024+820)=56% of the CPU >time and the NICE_1 task will get 44% of the CPU time. I'm obviously >not understanding something since I can't come at those 10% figures in >the comments. > >Thanks. > >_______________________________________________ >Kernelnewbies mailing list >Kernelnewbies(a)kernelnewbies.org >http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

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How to statically build kernel module?
by Kenneth Adam Miller Jan. 22, 2016

Jan. 22, 2016

Is there a guidance anywhere? I know my question is simple and straightforward, but I've looked around a bit and I can't find a direct way to statically build a kernel module into the kernel.

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CFS: Scheduler: How does each change in 'nice' value result in 10% change in CPU time?
by John Locke Jan. 22, 2016

Jan. 22, 2016

Can anyone explain how the weights that the 'nice' values are mapped to actually result in an ~10% change in CPU time as you go from one nice level to the next? I can't make out how the comment here actually computes: (https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/k…) /* * Nice levels are multiplicative, with a gentle 10% change for every * nice level changed. I.e. when a CPU-bound task goes from nice 0 to * nice 1, it will get ~10% less CPU time than another CPU-bound task * that remained on nice 0. * * The "10% effect" is relative and cumulative: from _any_ nice level, * if you go up 1 level, it's -10% CPU usage, if you go down 1 level * it's +10% CPU usage. (to achieve that we use a multiplier of 1.25. * If a task goes up by ~10% and another task goes down by ~10% then * the relative distance between them is ~25%.) */ static const int prio_to_weight[40] = { If I take an example of 2 tasks both with weight=1024 (NICE_0) they should each get 50% of the CPU time. If 1 of the tasks is reniced to NICE_1 then the NICE_0 task will get 1024/(1024+820)=56% of the CPU time and the NICE_1 task will get 44% of the CPU time. I'm obviously not understanding something since I can't come at those 10% figures in the comments. Thanks.

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PCI-Express Hotplug
by lifelong0811＠126.com Jan. 21, 2016

Jan. 21, 2016

Hi： Does somebody knows how the linux kernel implement the PCI-Express Hotplug. The process of the PCI-Express Hotplug is the same as the PCI hotplug? lifelong0811(a)126.com

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how to use wait_event_interruptible_timeout with less than 1 jiffie timeout?
by Daniel. Jan. 20, 2016

Jan. 20, 2016

Hi everybody, I have some code that convert an timeout comming from userspace (in ms) to jiffies prior passing to wait_event_interrupitible_timeout(). The code looks like this: unsigned long tout = user.timeout * HZ / 1000; /* convert from ms to jiffie */ int status = wait_event_interruptible_timeout(wq, cond, tout); I'm using HZ=100, the known default. The problem is: with HZ = 100 and user.timeout = 10 I have: 10 * 100 / 1000 = 1, This means that I can't use timeouts with less than 10ms. Is there any way to circunvent this without changing HZ value? Now let me explain why. I have a protocol running on linux that talk to other embedded systems in an master-slave way. This communication goes through some RF hardware. The communication is maded by master transmitting a frame and receiving another frame from slave. The slave takes about 2 ms to reply, but if the transmitting failed (because the slave was not listening or because the frame was corrupted while traveling through the air) the server has to transmit it again. Today I'm using 10ms as timeout because is the smaller amount that I known how to use, but if I can decrease this timeout to 2 or 3ms I would have a better performance in case of failures. Best regards, -- "Do or do not. There is no try" Yoda Master

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pci device driver
by Rabinarayan Panigrahi Jan. 20, 2016

Jan. 20, 2016

Hi, For understanding more about pci device driver i went though below links http://www.tldp.org/LDP/tlk/dd/pci.html and http://www.makelinux.net/ldd3/ chapter 12 but i am trying to understand a bit code side. can some one help me or any resources which will help me to understand more about it. Regards Rabi

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Found a problem so what next?
by John Whitmore Jan. 19, 2016

Jan. 19, 2016

I built and installed v4.4 on my laptop but Suspend no longer worked so I set about doing a git bisect to find the source of the problem. I've never had cause to use bisect before so if nothing else I'll have learned something. Anyhow got to an end point in git bisect of: john@bamboo:> git bisect bad Bisecting: 0 revisions left to test after this (roughly 0 steps) [b8b2c7d845d57f7a4b9f1f941f24728165e27626] base/platform: assert that dev_pm_domain callbacks are called unconditionally I was actually chuffed I got that far and it took a while as I was doing a "make mrproper" each time. I sort of assumed that I could just bisect and do a make, which would work out what it had to recompile, but then thought maybe that was a bit of an assumption. Be a shame to do all that work and find out you had to clean up a bit between builds. I'm sure that this problem has been found and a patch submitted by now as it seems to have been from months ago. But assuming neither had occured and this was a new discovery how do you check for a reported bug? Do you search mailing list for that commit number, or a part of that commit number? I read BUG-HUNTING in the documentation and it does mention: "Before you submit a bug report read REPORTING-BUGS." but can't see that document and it's not a section of BUG_HUNTING document. So what would the next step be? I'm sure fixing it would be one posibility but I've never looked at power management code so I'm not the person that should be let lose in there ;-) I had a look in journalctl but nothing in there suggests what the actual error is. I'll have a look at the log files some more and see if I can't get some sort of clue which would provide more info.

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Inexplicable PROT_EXEC flag set on mmap callback
by Kenneth Adam Miller Jan. 16, 2016

Jan. 16, 2016

I have a custom drive and userland program pair that I'm using for a very special use case at my workplace where we are mapping specific physical address ranges into userland memory with a mmap callback. Everything works together well with a C userland program that calls into our driver's ioctl and mmap definitions, but for our case we are using an alternative systems language just for the userland program. That mmap call is failing (properly as we want) out from the driver's mmap implementation due to the fact that the vm_flags have the VM_EXEC flag set. We do not want users to be able to map the memory range as executable, so the driver should check for this as it does. The issue is in the fact that somewhere between where mmap is called and when the parameters are given to the driver, the vma->vm_flags are being set to 255. I've manually checked the values being given to the mmap call in our non-C binary, and they are *equivalent* in value to that of the C program. My question is, is there anything that can cause the vma->vm_flags to be changed in the trip between when the user land program calls mmap and when control is delivered to the mmap callback?

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Re: Developing environments used for kernel development
by Daniel. Jan. 14, 2016

Jan. 14, 2016

Hey Jeff, thanks for the reply, what I realy don't like in IDEs is tying building and editing at same tool. I'm a simple guy so I like to keep things simple. I never heard of anybody using IDE's for building C code in linux. I'm considering back to vim since emacs indenting is making me crazy Regards 2015-12-22 17:59 GMT-02:00 Jeff Haran <Jeff.Haran(a)citrix.com>: > Off list. > > > > I use gvim, make, all the old style tools for kernel development and have > been doing so for about 15 years now, but I am an old fart. Your boss needs > to understand that a lot of these IDEs, though useful for user space > development, don’t help much in kernel space. When the kernel goes bad, the > IDE goes with it. > > > > If he is uneducatable on this, you might want to check out this package > called kdevelop. You can keep it running in one desktop to make him happy > and then do the real work using the tried and true command line tools in > another desktop. > > > > Good luck, > > > > Jeff Haran > > > > > > > > From: kernelnewbies-bounces(a)kernelnewbies.org > [mailto:kernelnewbies-bounces@kernelnewbies.org] On Behalf Of Daniel. > Sent: Tuesday, December 22, 2015 11:28 AM > To: kernelnewbies > Subject: Developing environments used for kernel development > > > > My boss came to my desk today raiging that I should use more productive > tools for developing. Well I don't want to begin an editor war but, yes, I > use emacs. I used to use vim before but the integration of emacs and gdb has > caught my attention. > > To be clear, as "more productive tools" he understands graphical eye candy > tools. My argument to use an "simple editor plus makefiles" was, it just > works and thats it. So before to downloading eclipse just to make my boss's > eyes happy I've decided to make a little research. > > What you guys are using today to develope kenrel code? > > > > Best Regards, > > - dhs > > > -- > > "Do or do not. There is no try" > Yoda Master -- "Do or do not. There is no try" Yoda Master

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