Messages in this thread | ![/](/images/icornerl.gif) | | From | Rusty Russell <> | Subject | Re: per_cpu fixes | Date | Fri, 11 Jul 2003 12:01:08 +1000 |
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In message <16141.43130.657025.952793@napali.hpl.hp.com> you write: > You mean there would be three primitives: > > (1) get value from a per-CPU variable > (2) set value of a per-CPU variable > (3) get the (canonical) address of a per-CPU variable > > ?
Almost, #3 would actually be "get lvalue", as now.
The only problem is that a quick audit of 2.5.75 reveals 16 places in generic code where set/get primitives would work without jumping through hoops, out of 43.
New idea:
Provide cpu_local_inc(var)/cpu_local_dec(var) and __cpu_local_inc(var) and __cpu_local_dec(var). Generic implementation:
/* This is local.h */ typedef atomic_t local_t;
#define local_inc(l) atomic_inc(l) #define local_dec(l) atomic_dec(l)
/* l is a per-cpu local_t. Increment it atomically. */ #define cpu_local_inc(l) local_inc(&__get_cpu_var(l)) #define cpu_local_dec(l) local_dec(&__get_cpu_var(l))
/* Increment non-atomically (must have preempt disabled) */ #define __cpu_local_inc(l) \ atomic_set(&__get_cpu_var(l), atomic_read(&__get_cpu_var(l)) + 1) #define __cpu_local_dec(l) \ atomic_set(&__get_cpu_var(l), atomic_read(&__get_cpu_var(l)) - 1)
This catches one common case for ia64 to use the magic pinned area, and also allows x86 to use its incl/decl instructions, which both networking stats and module refcounts have wanted for a while.
Thoughts? Rusty. -- Anyone who quotes me in their sig is an idiot. -- Rusty Russell. - 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/
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