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load balancing scheduler on linux
by Murali N Sept. 21, 2011

Sept. 21, 2011

Hi, Can somebody give pointers to the load balancing scheduler on Linux. I hope this is the default scheduler which is used on most of the linux systems on SMP environment. I would like to know how the scheduler takes a decision to migrate some of the processes to the another core? I have a scenario like below: If CORE0 is running per say 2 threads which can be handled by CORE0 itself ( by running at higher frequencies ) without enabling the CORE1 ( put into some low power mode ). How the scheduler takes this kind of decision intelligently!!! -- Regards, Murali N

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looking for 3.0 source
by Littlefield, Tyler Sept. 21, 2011

Sept. 21, 2011

Hello: With the recent attacks on kernel.org, it's down and I'm unsure of where to get what I want. I found the 2.6 branch on github, but I'm looking for kernel 3.0's source, not 3.4 or whatever we're on now. Is there somewhere I can get it? -- Take care, Ty Web: http://tds-solutions.net The Aspen project: a light-weight barebones mud engine http://code.google.com/p/aspenmud Sent from my toaster.

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How to deal with two tasks with the same virtual time
by Parmenides Sept. 21, 2011

Sept. 21, 2011

Hi, As far as the CFS scheduler is concerned, every task, whose key is the task's virtual time, will be inserted into a red-black tree to improve the performence of seaching specified task. But, that works well only if any task's vritual time is different with the others tasks'. So, I wonder whether there are chances that two tasks occasionally have the same virtual time. If so, how to deal with it?

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Why do the CFS chase fairness?
by Parmenides Sept. 20, 2011

Sept. 20, 2011

Hi, Current kernel 2.6 have adopted the CFS scheduler which try to ensure that all process can obtain their proportions of allotted processor fairly. I have three questions about it. 1. How to understand unfairness? I think unfairness is caused by processes sharing a processor, but I am not confident of it. According to Love, as far as fairness is concerned, if a processor is a perfectly multitasking processor, all of processes running on it should run simultaneously rather than run in turn. For example, there are two processes which have the same nice value. Both of them may run 10 ms on a perfectly multitasking processor, each at 50% of processor power. This kind of processor is prefect fair. In contrast, if the two processes run in turn on a real processor, each may run 5ms at 100% of processor power. Although in both of the two cases two processes run 10ms totally, but the latter case is unfair because one process runs first, the other has to wait for 5ms. In other words, when processes running on a real processor, some of them has to wait more or less until preceding processes use up their CPU shares. Does unfairness mean that? 2. Why do processes need fairness? Yes, we can argue that now that we human beings need fairness, processes do so. :-) But, are there advantages if the scheduler care about fairness? Just for processes not waiting too long? Or other reasons? 3. What's the drawbacks of traditional schdulers? According to Love, traditional schedulers assign each process a absolut timeslcie which yields a constant switching rate but variable fairness. How to understand 'constant switching rate'? What does cause 'variable fairness'?

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reading devices with input.h
by Volker Poplawski Sept. 20, 2011

Sept. 20, 2011

Hi all, what's the recommended method for processing input device data with linux/input.h (from userspace) ? blocking read()? non-blocking read()? select(), epoll()? Regards ......Volker

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2.6.39 Kernel Changes for FileSystem, get_sb removed
by Abhijit Pawar Sept. 20, 2011

Sept. 20, 2011

Hi list, It seems that the support for get_sb function is removed from kernel 2.6.39 onwards. My code which is working till 2.6.38 series is failing with new kernels. I tried finding out but there isnt anything mentioned. So if this function itself is removed then how kernel is going to find out the superblock and use it? Are we supposed to use the mount function provided? This is what i got from one of the kernel patch email. +[mandatory] + ->get_sb() is gone. Switch to use of ->mount(). Typically it's just +a matter of switching from calling get_sb_... to mount_... and changing the +function type. If you were doing it manually, just switch from setting ->mnt_root +to some pointer to returning that pointer. On errors return ERR_PTR(...). diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt It looks like there are other changes related to Pages are also done. Regards, Abhijit Pawar

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do_gettiimeofday query
by Lal Sept. 20, 2011

Sept. 20, 2011

I am having trouble with do_gettimeofday() function. I have following source code: int my_module_init(void) { struct timeval tv = {0}; do_gettimeofday(&tv); printk("tv.tv_sec = %lu\n", tv.tv_sec); return 0; } module_init(my_module_init); This code is built-in kernel, and therefore my_module_init is called during device_initcall. However the tv_sec value seems to be wrong (I was expecting this value to be absolute number of seconds since 1970), but it prints 11 or 12 (which seems to be number of seconds since last boot). I checked do_gettimeofday function source which gets the value from xtime variable. I could not find who is responsible for initializing xtime. I tried to change module_init by late_initcall_sync. Still it's same. Any help is appreciated. Regards Lal

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profiling functions called in interrupt context
by Amit Nagal Sept. 20, 2011

Sept. 20, 2011

Hi , i want to measure time spend in a callback function called from interrupt context . since the time spend will be in us / ns , what kernel apis can i use to measure it ? also since i want to use it in interrupt context , kernel time measurement apis should not sleep . i am using embedded arm target , and tools like OProfile are not available . can i be guided which kernel time measurement apis shall i use to measure time in a interrupt callback ? Regards Amit Nagal

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kernel crash dump analysis using crash utility
by amit mehta Sept. 19, 2011

Sept. 19, 2011

My Linux box just crashed while performing some network related tests. I'm trying to analyze the kernel crash dump using "Crash" utility. Need your help in analyzing it. <<<Snip from crash output>>> # crash /usr/lib/debug/lib/modules/2.6.32-131.0.15.el6.x86_64/vmlinux vmcore .........versioning information here............... .................etc etc.......................... KERNEL: /usr/lib/debug/lib/modules/2.6.32-131.0.15.el6.x86_64/vmlinux DUMPFILE: vmcore [PARTIAL DUMP] CPUS: 32 DATE: Mon Sep 19 09:44:45 2011 <---- --- UPTIME: 2 days, 22:55:44 LOAD AVERAGE: 0.00, 0.02, 0.00 TASKS: 409 NODENAME: RHEL61ga RELEASE: 2.6.32-131.0.15.el6.x86_64 VERSION: #1 SMP Tue May 10 15:42:40 EDT 2011 MACHINE: x86_64 (2660 Mhz) MEMORY: 12 GB PANIC: "Oops: 0000 [#1] SMP " (check log for details) PID: 0 COMMAND: "swapper" TASK: ffffffff81a2d020 (1 of 8) [THREAD_INFO: ffffffff81a00000] CPU: 0 STATE: TASK_RUNNING (ACTIVE) WARNING: panic task not found ........................ stack trace frame 0 - frame 18 here..................... ............................................................................................... --- <IRQ stack> --- #19 [ffffffff81a01da8] ret_from_intr at ffffffff8100bad3 [exception RIP: acpi_check_resource_conflict+207] < ---- --- -------- RIP: ffffffff812bb86e RSP: ffffffff81a01e58 RFLAGS: 00000206 RAX: 0000000000000000 RBX: ffffffff81a01ec8 RCX: 0000000000000000 RDX: 0000000000000006 RSI: 0000000000000000 RDI: 00000000000018f6 RBP: ffffffff8100bace R8: 0000000000000000 R9: 0000000000000ca3 R10: ffff88019aa061c2 R11: ffff88019aa06201 R12: ffffffff81b7c0b8 R13: 0000000000000001 R14: ffffffff810ece03 R15: ffffffff81a01dd8 ORIG_RAX: ffffffffffffffb5 CS: 0010 SS: 0018 #20 [ffffffff81a01e50] acpi_check_resource_conflict at ffffffff812bb851 #21 [ffffffff81a01ed0] show_current_driver at ffffffff813eccb7 #22 [ffffffff81a01ef0] cpu_idle at ffffffff81009e96 <<<Snip from crash output>>> Observation: i) The panic hit at Sep 19 09:44:45 2011, and a peek inside /var/log/messages reveals that the machine was down for about 4-5 minutes around this timestamp. But there are no other relevant information available in the log file, so as printed in the panic string above: "Oops: 0000 [#1] SMP " (check log for details)", where else should i look for logs ? ii) Does frame 19:: [exception RIP: acpi_check_resource_conflict+207] and the immediated dump of the registers of my machine(Mine is x86_64) is an indication of where the Oops occured ? iii) Disassembly of "acpi_check_resource_conflict" at an offset:207 shows a 'test' instruction being carried out on CPU 0: 0xffffffff812bb86e <acpi_check_resource_conflict+207>: test %ebx,0xc4c3e8(%rip) # 0xffffffff81f07c5c iv) I belive that on 64 bit x86 machines, RIP represents EIP and similarly RBX represents EBX register. hence at the time of panic, the contents fo these registers were as follows: RBX = ffffffff81a01ec8 RIP = ffffffff812bb86e I don't know much of assembly, just did little bit of search on web, and my understanding is that the instruction "test %ebx,0xc4c3e8(%rip)" tells the processor to do the bitwise "and" of contents of ebx register with the value at the offset:0xc4c3e8 from the base address pointed by rip. i.e. ffffffff812bb86e+c4c3e8 = FFFFFFFF81F07C56 ? Please correct me if I'm wrong. -Amit

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how to use hashmap in kernel module?
by Jon Zhou Sept. 19, 2011

Sept. 19, 2011

Hi I want to hashmap to store datat in kernel module, how can I do this? Any existed code? Thanks jon

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