Also, what does "relocation truncated to fit: R_PPC_REL24
atomic_inc(atomic_t
quoted
*)" mean?
About as much as 'unresolved external reference'. atomic_inc isn't
defined
in the scope of your code. Look at the kernel headers; it might be
inside
#ifdef __KRENEL__ (actually it is).
I see... when I wrote the code using Red Hat, this was not the case. I
assumed
things would be similar under all Linuxes... apparently a bad
assumption.
Why do you think you need to use atomic_inc directly instead of some
pthreads wrapper?
I wasn't able to find a decent equivalent to atomic_t in the pthreads
API.
The closest thing I could see would be to wrap my counter increments/
decrements in a pthread_mutex_t to serialize them, but creating a
separate mutex for each atomic counter seems a bit expensive/
inefficient, considering there may be thousands of such atomic counters
active at once. Is there some other way to use pthreads to get an
atomic counter? Or is a pthread_mutex_t really efficient enough to
make a decent atomic counter out of? Or do I need to redesign how my
application works, because there is no good way to do a cheap, portable
user-land atomic counter under Linux? :^(
Jeremy
** Sent via the linuxppc-dev mail list. See http://lists.linuxppc.org/
From: Michael Schmitz <hidden> Date: 2002-01-04 17:44:03
quoted
quoted
Also, what does "relocation truncated to fit: R_PPC_REL24
atomic_inc(atomic_t
quoted
quoted
*)" mean?
About as much as 'unresolved external reference'. atomic_inc isn't
defined
quoted
in the scope of your code. Look at the kernel headers; it might be
inside
quoted
#ifdef __KRENEL__ (actually it is).
I see... when I wrote the code using Red Hat, this was not the case. I
assumed
things would be similar under all Linuxes... apparently a bad
assumption.
It's a kernel or libc header issue - what kernel/libc version was that
on? As far as I can see atomic operations are exported to user programs
except on ppc (not ppc64), mips*, arm and sparc. At least in one case it's
obvious why: MIPS needs to protect against interrupts to guarantee
atomicity.
Another corner case seems to be IBM 405 processors that use what I think
is a privileged instruction as well in order to work around a hardware
bug.
quoted
Why do you think you need to use atomic_inc directly instead of some
pthreads wrapper?
I wasn't able to find a decent equivalent to atomic_t in the pthreads
API.
pthreadss only came to mind first, there may be other packages. Point
being, on those architectures that cannot guarantee atomic operations
using nonprovileged instructions there has to be some sort of kernel
cooperation (system call?).
The closest thing I could see would be to wrap my counter increments/
decrements in a pthread_mutex_t to serialize them, but creating a
separate mutex for each atomic counter seems a bit expensive/
inefficient, considering there may be thousands of such atomic counters
active at once. Is there some other way to use pthreads to get an
atomic counter? Or is a pthread_mutex_t really efficient enough to
I have no experience with pthreads, sorry.
make a decent atomic counter out of? Or do I need to redesign how my
application works, because there is no good way to do a cheap, portable
user-land atomic counter under Linux? :^(
Worst-case? The latter. At least for MIPS there doesn't seem to be such a
thing as atomic user land operations. How they would implement a mutex
without those, I wonder ...
You can try to copy the atomic ops from the kernel headers for those
architectures lacking them, hoping it won't break. If it doesn't, you have
a good argument in favor of removing the #ifdef __KERNEL__ :-)
Michael
** Sent via the linuxppc-dev mail list. See http://lists.linuxppc.org/
From: Kevin B. Hendricks <hidden> Date: 2002-01-04 18:33:32
Hi,
There are a number of places you can get atomic increment and decrement
code:
1. borrow the implementations from the kernel
2. look at www.openOffice.org CVS sal/osl/unx/interlck.c
for atomic increment and decrement code for both x86 linux and ppc
linux, and the proper includes for Solaris.
3. adapt the code from
glibc-2.2.4/linuxthreads/sysdeps/powerpc/pt-machine.h for "compare
_and_swap" and "test_and_set" t do your own "dec_and_test"
4. simply use a pthread mutex to protect the counter (complete overkill)
5. look at the implementations of these synchronization functions in the
IBM/Motorola PowerPC Microprocessor Family: The Programming Environment"
manual (available as a pdf from the Motorola site). They have
implementations for "Fetch and Add", "Test and Set" , "Compare and Swap"
"Lock Acquisition and Release" and "List Insertion"
I personally recommend using the code from interlck.c from OpenOffice as
your guide and falling back to using a mutex to protect the count for
unknown processors. That way it will always work but if performance is an
issue, someone can add the support for other processors. This is what
OpenOffice does for its refernce counted strings.
Hope this helps,
Kevin
On January 4, 2002 12:00, jaf wrote:
Hi Michael,
quoted
quoted
Also, what does "relocation truncated to fit: R_PPC_REL24
atomic_inc(atomic_t
quoted
quoted
*)" mean?
About as much as 'unresolved external reference'. atomic_inc isn't
defined
quoted
in the scope of your code. Look at the kernel headers; it might be
inside
quoted
#ifdef __KRENEL__ (actually it is).
I see... when I wrote the code using Red Hat, this was not the case. I
assumed
things would be similar under all Linuxes... apparently a bad
assumption.
quoted
Why do you think you need to use atomic_inc directly instead of some
pthreads wrapper?
I wasn't able to find a decent equivalent to atomic_t in the pthreads
API.
The closest thing I could see would be to wrap my counter increments/
decrements in a pthread_mutex_t to serialize them, but creating a
separate mutex for each atomic counter seems a bit expensive/
inefficient, considering there may be thousands of such atomic counters
active at once. Is there some other way to use pthreads to get an
atomic counter? Or is a pthread_mutex_t really efficient enough to
make a decent atomic counter out of? Or do I need to redesign how my
application works, because there is no good way to do a cheap, portable
user-land atomic counter under Linux? :^(
From: Kevin B. Hendricks <hidden> Date: 2002-01-04 18:57:07
Hi,
One other thing, PPC implements synchronization using a reservation bit
for specific address with a special instruction pair that sets and clears
the reservation. But the address to set/clear the reservation on is only
unique down the the cache line size (in most cases 32 bytes for ppc) i.e.
the reservation granularity.
In English, what this means is that if two counters you want to atomically
increment or decrement are stored within 32 bytes of each other and
different threads are simulataneously trying to increment or decrement
them, the reservation can get spurious clears that prevents either one
from working without more looping (i.e performance starts to suffer).
In practive I have very very rarely ever seen this problem have an impact
on anything. Others may know more.
Hope this helps,
Kevin
On January 4, 2002 01:33, Kevin B. Hendricks wrote:
Hi,
There are a number of places you can get atomic increment and decrement
code:
1. borrow the implementations from the kernel
2. look at www.openOffice.org CVS sal/osl/unx/interlck.c
for atomic increment and decrement code for both x86 linux and ppc
linux, and the proper includes for Solaris.
3. adapt the code from
glibc-2.2.4/linuxthreads/sysdeps/powerpc/pt-machine.h for "compare
_and_swap" and "test_and_set" t do your own "dec_and_test"
4. simply use a pthread mutex to protect the counter (complete overkill)
5. look at the implementations of these synchronization functions in the
IBM/Motorola PowerPC Microprocessor Family: The Programming Environment"
manual (available as a pdf from the Motorola site). They have
implementations for "Fetch and Add", "Test and Set" , "Compare and Swap"
"Lock Acquisition and Release" and "List Insertion"
I personally recommend using the code from interlck.c from OpenOffice as
your guide and falling back to using a mutex to protect the count for
unknown processors. That way it will always work but if performance is
an issue, someone can add the support for other processors. This is
what OpenOffice does for its refernce counted strings.
Hope this helps,
Kevin
On January 4, 2002 12:00, jaf wrote:
quoted
Hi Michael,
quoted
quoted
Also, what does "relocation truncated to fit: R_PPC_REL24
atomic_inc(atomic_t
quoted
quoted
*)" mean?
About as much as 'unresolved external reference'. atomic_inc isn't
defined
quoted
in the scope of your code. Look at the kernel headers; it might be
inside
quoted
#ifdef __KRENEL__ (actually it is).
I see... when I wrote the code using Red Hat, this was not the case.
I assumed
things would be similar under all Linuxes... apparently a bad
assumption.
quoted
Why do you think you need to use atomic_inc directly instead of some
pthreads wrapper?
I wasn't able to find a decent equivalent to atomic_t in the pthreads
API.
The closest thing I could see would be to wrap my counter increments/
decrements in a pthread_mutex_t to serialize them, but creating a
separate mutex for each atomic counter seems a bit expensive/
inefficient, considering there may be thousands of such atomic
counters active at once. Is there some other way to use pthreads to
get an atomic counter? Or is a pthread_mutex_t really efficient
enough to make a decent atomic counter out of? Or do I need to
redesign how my application works, because there is no good way to do
a cheap, portable user-land atomic counter under Linux? :^(
On Fri, Jan 04, 2002 at 06:44:03PM +0100, Michael Schmitz wrote:
quoted
quoted
quoted
Also, what does "relocation truncated to fit: R_PPC_REL24
atomic_inc(atomic_t
quoted
quoted
*)" mean?
About as much as 'unresolved external reference'. atomic_inc isn't
defined
quoted
in the scope of your code. Look at the kernel headers; it might be
inside
quoted
#ifdef __KRENEL__ (actually it is).
I see... when I wrote the code using Red Hat, this was not the case. I
assumed
things would be similar under all Linuxes... apparently a bad
assumption.
A userspace app using <asm/*.h> and <linux/*.h> is quite probably a bug.
If you need something from the kernel, make a local copy and never,
ever, ever, reference it directly, since it can change on you.
--
Tom Rini (TR1265)
http://gate.crashing.org/~trini/
** Sent via the linuxppc-dev mail list. See http://lists.linuxppc.org/
From: Frank Rowand <hidden> Date: 2002-01-04 19:50:44
Michael Schmitz wrote:
quoted
quoted
quoted
Also, what does "relocation truncated to fit: R_PPC_REL24
atomic_inc(atomic_t
quoted
quoted
*)" mean?
About as much as 'unresolved external reference'. atomic_inc isn't
defined
quoted
in the scope of your code. Look at the kernel headers; it might be
inside
quoted
#ifdef __KRENEL__ (actually it is).
I see... when I wrote the code using Red Hat, this was not the case. I
assumed
things would be similar under all Linuxes... apparently a bad
assumption.
It's a kernel or libc header issue - what kernel/libc version was that
on? As far as I can see atomic operations are exported to user programs
except on ppc (not ppc64), mips*, arm and sparc. At least in one case it's
obvious why: MIPS needs to protect against interrupts to guarantee
atomicity.
Another corner case seems to be IBM 405 processors that use what I think
is a privileged instruction as well in order to work around a hardware
bug.
The dcbt instruction (the workaround) should not be privileged.
< stuff deleted >
-Frank
--
Frank Rowand [off-list ref]
MontaVista Software, Inc
** Sent via the linuxppc-dev mail list. See http://lists.linuxppc.org/