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Joseph D. Wagner | 20 May 2013 07:28

kdump fails on encrypted root

I can get kdump to work with encrypted root in kvm, but not on raw iron.

Can anyone help me figure out how to get it working?
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Joseph D. Wagner | 14 May 2013 01:28

Excessive Swapping Under Minimal Load

I am trying to use duplicity to backup my /home to an external hard 
drive
(usb 2 interface).  After running for a few minutes, my io slows to a 
crawl.
My system reports using about 300-400MB of swap, even though only about
600MB / 4GB is in use.

I am trying to isolate the cause.  It may be duplicity in conjunction 
with
the particulars of my configuration (see below).  I get good 
performance
under normal circumstances.  I am using fedora 18, which has /tmp 
mounted
using tmpfs, but duplicity never uses more than 1.0GB - 1.1GB.

First, is this the correct forum for asking for this kind of help?

Second, what information

The particulars of my configuration:
sda1 -> win7 hidden boot
sda2 -> win7 regular
sda3 -> grub2 boot
sda5 -> luks swap
sda6 -> luks ext4 root
sda7 -> regular ext4 data
sdb1 -> luks userdata1 -> md raid 0 with userdata1 & userdata2-> ext4 
home
sdc1 -> luks userdata2 -> md raid 0 with userdata1 & userdata2-> ext4 
home
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Ashoka K | 30 Apr 2013 10:27
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Need help to measure and tune the latency in Linux RT

Hi,

I have an embedded system running 2.6.33 cross compiled for ARM OMAP
with 1 GHZ uni-processor system.

The application has many threads and processes (around 15 total). In
that 1 thread is time critical and must run every interval confiurable
as 2, 4 or 8 milli sec etc. There is another thread which transfers
Images to a FTP or to HMI etc, whoever requested the image.
With this image transfer enabled my critical process misses the
deadline and timesout. This critical thread is at RR priority 50. I
used a HR timer thread with RR pri 55 to wakeup the critical thread
every 1 milli sec to do the job.
If image transfer is enabled i see that real time thread misses deadlines.

All traffic is flowing on common ethernet connection. Does it affect
in any way ?

How to find out where the kernel is waiting or delaying to schedule
the critical thread even though it is at higher RR priority. How to
measure the latency ?

I am trying to use Oprofile tool, but got some error in cross
compiling. Doesn't these tools add their own latency to the original
problem ?

Any tools ? which one is better. Please provide your input on this.

Regards
Ashoka.  K
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Ryan | 29 Apr 2013 10:30

A spinlock_irqsave question

Hi,

I have a question on spinlock_irqsave api. Am not sure if this is the
right place to ask.
Any help is highly appreciated.

let me know if my understanding is correct?

spinlock_irqsave()  <== Disables the IRQ?

                            <== No IRQs (that means no KB
interrupt,Interrupts from touch screen... etc..)

spinlock_irqrestore()

Is my understanding correct?
So the "time spend between spinlock_irqsave and spinlock_restore
should be very short?

For example there should not be something like this? Am i correct?

spinlock_irqsave()

mdelay(1000);

spinlock_irqrestore()

Also, what is meant by "spinlock_irqsave" disabled irq locally?

What is locally here?
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disnoir | 24 Apr 2013 19:18
Picon

How could I record the information when kernel panic.

There is a random probability that cause the kernel panic (debian with 
kernel 3.2.41), when I execute:
"sudo umount /media/data /media/big".

Things are like this:

I use "udisks --mount /dev/sda3" to mount "data" which is a ntfs filesystem.
similarly, I use "udisks --mount /dev/wd5000bpvt/big" to mount "big" 
which is a ext4 filesystem.

After finish using these filesystems, I use "sudo umount /media/data 
/media/big" to umount the filesystems, and the hole system just suddenly 
halt (mouse is not moving).

using alt-sysrq-b to reboot the system. nothing record in the 
/var/log/messages.

So, How could I record the kernel error/info, when system was halt ?

Thanks a lot!

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ishare | 6 Apr 2013 15:46
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how does ld.so transfer execution to executable section ?


  At boot stage ,the process 1 will execute '/bin/sh' . as it needs ld.so to help loading other .so ,
  it loads ld.so into memory and execute ld.so first .

  My question is when and how does ld.so transfer its execution to code of /bin/sh ?

  Thanks!
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Jayram Déshpandé | 1 Apr 2013 07:11
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Gravatar

mapping memory reserved by "memmap" kernel boot param into user space

Hello ,

As discussed in this[1] discussion, i am reserving a memory chunk at the
boot time using a kernel boot parameter memmap=8G$64G

I have written a character driver [2] kernel module which , during
initialization does a ioremap of this reserved memory chunk. As explained
here , in my driver mmap all i need to do is remap_pfn_range for this
memory chunk pointer returned by the ioremap.

I am running this on 3.x linux kernel. My user space application opens this
memory chunk as a device mounted by the driver. When i do mmap from the use
space application i see a system hang. my dmesg don't provide me much
information.

So questions are :

1 ) Does  remap_pfn_range function have some upper limit on the size of the
memory that can be remaped to ? Note that i am trying to reserve a
comparatively large chunks of memory at the boot time of the order of 64GB
to about 150GB. The system can have 128 to 256 GB of ram.

2) I tried by disabling the ioremap from the initialization and thus
directly doing the page frame numbers remapping in the mmap ioctl routing.
But that also results in a hang.

3) I tried with a page-fault handler , but that doesn't seem to help either.

Regards,
-Jay
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ishare | 30 Mar 2013 10:11
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init file for boot


  After kernel mount the real device to "/" , is the initramfs still  usefull ? If so ,it is mounted at which entry?

  At the end stage of boot , kernel will execute a init file , 
  whether this file locates at initramfs address space  *or*  the device mounted at "/" ?

  I feel confused  of  this point .
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ishare | 29 Mar 2013 12:33
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can not find definition of ntohl


 why I have not find the definiton of ntohl in kernel source ?

 is there anyone can give some clues to me ?

 thanks!
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ishare | 27 Mar 2013 14:17
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Mount two device on the same directory


  Can I mount two different device on the same dir ?

  If I first mount a superblock of vitual filesystem on / ,

  then I mount another real device /dev/sda1 also on / ,

  then, if I type " ls / " command , Are all files in the two device show up to me?

  thanks!

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ishare | 26 Mar 2013 14:21
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call stack of a system call


  At user level ,is there system interface to help printing the call stack of one system api ?

  for example: I want to print the send/receive call stack from kernel , is there 
  helper for user application to achieve this?  

  thanks!
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