Messages in this thread |  | | Date | Sat, 23 Feb 2002 12:06:48 -0700 | From | yodaiken@fsmlabs ... | Subject | Re: [PATCH] only irq-safe atomic ops |
| |
On Sat, Feb 23, 2002 at 01:20:06PM -0500, Robert Love wrote: > On Sat, 2002-02-23 at 06:38, yodaiken@fsmlabs.com wrote: > > > So without preemption in the kernel > > maybe 4 instructions: calculate cpuid, inc; all local no cache ping > > code is easy to read and understand. > > > > with preemption in the kernel > > a design problem. a slippery synchronization issue that > > involves the characteristic preemption error - code that works > > most of the time. > > Or not. The topic of this thread was a micro-optimization. If we treat > the variable as anything normal requiring synchronization under SMP, any > of the standard solutions (atomic ops, etc.) work. If we want to get
And cause cache ping, possible contention, ...
> fancy, we can disable preemption, use my atomic_irq ops, or just not > care.
Right. Without preemption it is safe to do c = smp_get_cpuid(); ... x = ++local_cache[c] ..
y = ++different_local_cache[c]; ..
With preemption this turns into a problem that is easier to solve with a lock or by not having per-cpu caches in the first place -- eg by writing worse code. After all, those are just micro-optimizations and a few percent here, a few percent there, nobody will notice it. -(
-- --------------------------------------------------------- Victor Yodaiken Finite State Machine Labs: The RTLinux Company. www.fsmlabs.com www.rtlinux.com
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
|  |