[haiku-kernel-devel] About Contributing to kernel

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[haiku-kernel-devel] driver unloading

Hi,

I'm having a go at writing an ACPI driver for changing the brightness of my laptop screen from within Haiku.
To get started, I have copied the source code for the battery driver and threw most of the function contents
out. After copying the driver to /boot/home/add-ons/kernel/drivers/power and rebooting, I can get
some output from 'cat /dev/power/acpi_backlight'. Rene told me the driver should unload after that, and
the syslog shows this indeed:
KERN: acpi_backlight: acpi_backlight_init_device
KERN: acpi_backlight: acpi_backlight_open
KERN: acpi_backlight: acpi_backlight_read
Last message repeated 1 time
KERN: acpi_backlight: acpi_backlight_close
KERN: acpi_backlight: acpi_backlight_free
KERN: acpi_backlight: acpi_backlight_uninit_device

However, after changing the driver, recompiling and copying it again, the changes are not visible on a new
cat. Listimage shows it's still loaded:

$ listimage 1 | grep backlight
  349         /boot/system/add-ons/kernel/drivers/power/acpi_backlight 0x807f4000 0x807f6000    0          0

For the atheros driver, issuing ifconfig down, makes the driver print to the syslog:
KERN: [net/atheroswifi/0] compat_free()

And also here, listimage still shows it.

So, what is broken? Or more likely, what am I doing wrong? :)

I just discovered this message: http://article.gmane.org/gmane.os.haiku.devel/8575
I'll try placing the driver under /boot/system...

Kind regards,
Brecht

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IOCache vs. block cache

Howdy,

I've been meditating a bit on how the block cache is favored over the file 
cache ATM. The problem is that the file cache smoothly integrates with the 
page allocation backend -- i.e. when there are no/too few free pages 
available, cached pages are recycled -- while the block cache grows 
unboundedly until a low resource limit is hit (pages, memory, or address 
space). The pages limit cannot be reached as long as there still are cached 
pages, so, unless memory or address space limit are hit first, as soon as 
all pages are used (actually or for caching) the block cache starts 
draining the file caches. I.e. very old cached blocks are favored over 
increasingly newer cached file content.

I think eventually the block cache should be rewritten to be VMCache based 
with on-demand mapping of hot blocks, but for the time being a simpler 
solution would be possible: The IOCache could be extended to make it 
possible to lay it under the IOSchedulerSimple. This would give us a 
VMCache based cache close to the device. The block cache could then work 
with a very small, limited (!) set of unused blocks.

The advantages are:

* The block cache would no longer exert any memory pressure.

* The real caching happens in the IOCache, which integrates smoothly with 
the page allocation backend. The file cache is no longer at a disadvantage.

* There won't be anymore double-caching when mounting image files (file 
cache for the file, block cache for the FS on top of it).

* Since the block cache is rather dumb ATM, there's some chance of serious 
performance improvements, particulary when assuming that FSs store related 
data close to each other. The block cache reads individual blocks, the 
IOCache always reads whole cache lines. So we'd automatically get 
pre-caching.

The only disadvantage I see is the double caching for file content: The 
IOCache caches at device level, the file caches at file level. On the 
bright side, if the the file content is actually read again later, the 
cached pages in the IOCache will eventually be recycled, while the file 
cache pages will prevail. Writes to the file will refresh the IOCache pages 
as well, though. OTOH less aggressive caching in the file cache (e.g. 
detect contiguous reads/writes and drop older pages early) would improve 
the situation -- incorrectly predicted future access behavior would be 
rather harmless.

I haven't looked into the USB mass storage situation yet. There might be 
additional advantages or disadvantages in this department.

CU, Ingo

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IPv6 protocol stack development

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GSoc 2010: File system cache or Kernel as userland process

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Increase syslog_buffer_size

Hi,
I'd like to increase the syslog_buffer_size to 1024000 (~ 1 MB) for the 
purpose of getting rid of the DROP and TRUNC messages when inspecting 
syslog of WiFi-driver systems. This would make debugging Wifi issues a 
lot easier, as the syslogs can be directly used instead of requesting to 
increase the syslog_buffer_size first to get a new syslog.

I know this value is high, but previous public testing of the 
atheroswifi driver showed that everything below that value still 
generates the DROP and TRUNC (though less often).

I think my request would be a candidate for a vote, so would this list 
be the correct place for this? Or would such a vote be better suited for 
the haiku-development list?

Kind Regards
-Colin

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Adding strndup to kernel

Hi,

would it be ok to add strndup.cpp to kernel_lib_posix.o?
I'd like to make use of it in the freebsd compat layer, where a string 
(originating in FreeBSD driver code) has to be duplicated and I have a 
bad feeling about using strdup for it.
I know of alternative approaches to implement a safe copy, but I wanted 
to ask first.

Kind Regards
Colin

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Signals and preemption-related question

Hi,

Michael and I were having a discussion about the current behavior with
respect to preemption on release_sem_etc and/or signal delivery, and
an uncertain question crops up: In quite a few cases, if a thread is
woken up by either one, that wakeup is being used as a communications
mechanism between two threads (i.e. to wake up another thread and tell
it data is ready to be worked on). However, the scheduler currently
only preempts if the new thread's priority is greater than that of the
instigator. In cases like this though, it's entirely possible the two
threads will be of equal priority, and as such that strategy might
result in undesired latency on waking up the recipient since the
sender will be allowed the rest of its timeslice. However, at the same
time, if we did signal preemption on equal priority, there's still no
guarantee that the target thread will in fact be the one woken up due
to a) the 20% random factor we use for priority skipping, and b) the
fact that we enqueue new threads at the end of the list of waiting
threads at the same priority, and as such if another is waiting it
will go first (if it goes at all). Is this a situation we want to deal
with, and if so, any thoughts on how?

Regards,

Rene

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Fwd: Re: Core Topology

Hi,

it looks like my previos mail never made it to the list. I'm resending it.

From: Marcus Overhagen <marcusoverhagen@...>
Subject: Re: [Open-beos-kernel-devel] Core Topology
Date: 2009-04-08 22:37:57 GMT

Christian Packmann schrieb:

> The current implementation in Haiku only allows CPUID input in register 
> EAX; some recent CPUID functions on Intel also require an input in ECX to 
> indicate the requested level of the topology. So there needs to be a new 
> CPUID wrapper which also allows for inputs to ECX. I already mentioned 

We could add an
get_cpuid_etc(cpuid_info *, const cpuid_params *, uint32 flags)

struct cpuid_params {
   uint32	cpuNum;
   uint32	eax;
   uint32	ebx;
   uint32	edx;
   uint32	ecx;
};

Or we use a macro as in get_sem_info and break source compatibility.

status_t get_cpuid(cpuid_info *info, uint32 eaxRegister, uint32 cpuNum);
status_t _get_cpuid_etc(cpuid_info *, const cpuid_params *);

#define get_cpuid(info, param) _get_cpuid_etc(info, param)

which would overlay get_cpuid calls while still retaining binary 
compatibility.

optionally, extend the cpuid_info struct

typedef union {
[...]
   struct {
     uint32	eax;
     uint32	ebx;
     uint32	edx;
     uint32	ecx;
   } inputs;
} cpuid_info;

instead of adding the params struct.

regards
Marcus

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Core Topology

Hi,

Are there any plans to implement a mechanism by which a scheduler
could discover the topology of the detected CPUs/cores/hardware
threads? If not, any preference on what such an API should look like?

Regards,

Rene

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