* MIPS atomic operations, "sync"
@ 2006-11-10 18:40 Mathieu Desnoyers
2006-11-10 22:33 ` Ralf Baechle
0 siblings, 1 reply; 3+ messages in thread
From: Mathieu Desnoyers @ 2006-11-10 18:40 UTC (permalink / raw)
To: linux-kernel, ltt-dev
Hi,
I am currently creating a "LOCK" prefix free and memory barrier free version
of atomic.h to fulfill my tracer (LTTng) needs, which is to atomically update
per-cpu data and have a minimal performance loss.
I just came across the MIPS atomic.h and system.h implementations in 2.6.18
which brings a question :
Why are the primitives in include/asm-mips/atomic.h using the "sync"
instruction even in the UP case ? system.h cmpxchg only uses the sync in the
SMP case.
Mathieu
OpenPGP public key: http://krystal.dyndns.org:8080/key/compudj.gpg
Key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: MIPS atomic operations, "sync"
2006-11-10 18:40 MIPS atomic operations, "sync" Mathieu Desnoyers
@ 2006-11-10 22:33 ` Ralf Baechle
2006-11-11 5:13 ` Mathieu Desnoyers
0 siblings, 1 reply; 3+ messages in thread
From: Ralf Baechle @ 2006-11-10 22:33 UTC (permalink / raw)
To: Mathieu Desnoyers; +Cc: linux-kernel, ltt-dev
On Fri, Nov 10, 2006 at 01:40:49PM -0500, Mathieu Desnoyers wrote:
> I am currently creating a "LOCK" prefix free and memory barrier free version
> of atomic.h to fulfill my tracer (LTTng) needs, which is to atomically update
> per-cpu data and have a minimal performance loss.
>
> I just came across the MIPS atomic.h and system.h implementations in 2.6.18
> which brings a question :
>
> Why are the primitives in include/asm-mips/atomic.h using the "sync"
> instruction even in the UP case ? system.h cmpxchg only uses the sync in the
> SMP case.
Why are the standard atomic operations insufficient for your needs?
There is an enormous amout of subtilities in those atomic ops for some
architectures you probably do yourself a big favor by avoiding new
variants.
Ralf
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: MIPS atomic operations, "sync"
2006-11-10 22:33 ` Ralf Baechle
@ 2006-11-11 5:13 ` Mathieu Desnoyers
0 siblings, 0 replies; 3+ messages in thread
From: Mathieu Desnoyers @ 2006-11-11 5:13 UTC (permalink / raw)
To: Ralf Baechle; +Cc: linux-kernel, ltt-dev
* Ralf Baechle (ralf@linux-mips.org) wrote:
> On Fri, Nov 10, 2006 at 01:40:49PM -0500, Mathieu Desnoyers wrote:
>
> > I am currently creating a "LOCK" prefix free and memory barrier free version
> > of atomic.h to fulfill my tracer (LTTng) needs, which is to atomically update
> > per-cpu data and have a minimal performance loss.
> >
> > I just came across the MIPS atomic.h and system.h implementations in 2.6.18
> > which brings a question :
> >
> > Why are the primitives in include/asm-mips/atomic.h using the "sync"
> > instruction even in the UP case ? system.h cmpxchg only uses the sync in the
> > SMP case.
>
> Why are the standard atomic operations insufficient for your needs?
>
> There is an enormous amout of subtilities in those atomic ops for some
> architectures you probably do yourself a big favor by avoiding new
> variants.
>
Performance cost.
I add a memory barrier where needed when the data needs to appear to be written
sequentially from the other CPUs perspective.
Mathieu
OpenPGP public key: http://krystal.dyndns.org:8080/key/compudj.gpg
Key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
^ permalink raw reply [flat|nested] 3+ messages in thread
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2006-11-10 18:40 MIPS atomic operations, "sync" Mathieu Desnoyers
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