Messages in this thread | | | From | Rusty Russell <> | Subject | Re: [PATCH] kmalloc_percpu | Date | Tue, 06 May 2003 10:47:20 +1000 |
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In message <20030505014729.5db76f70.akpm@digeo.com> you write: > Rusty Russell <rusty@rustcorp.com.au> wrote: > > > > This is the kmalloc_percpu patch. > > How does it work? What restrictions does it have, and > what compromises were made? > > +#define PERCPU_POOL_SIZE 32768 > > What's this?
OK. It has a size restriction: PERCPU_POOL_SIZE is the maximum total kmalloc_percpu + static DECLARE_PER_CPU you'll get, ever. This is the main downside. It's allocated at boot.
The __alloc_percpu allocator is extremely space efficient, by not insisting on cache-line aligning everything: __alloc_percpu(SIZE) overhead is sizeof(int), plus SIZE bytes (rounded up to alignment requirements) removed from per-cpu pool.
The allocator is fairly slow: they're not expected to be thrown around like candy.
> The current implementation of kmalloc_per_cpu() turned out to be fairly > disappointing because of the number of derefs which were necessary to get at > the data in fastpaths. How does this implementation compare?
It uses the same method as the static ones, so it's a single addition of __per_cpu_offset (assuming arch doesn't override implementation). This is a requirement for modules to use them (which was my aim: the other side effects are cream).
Hope that clarifies, 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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