Messages in this thread |  | | Date | Wed, 10 Oct 2001 02:36:13 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: [Lse-tech] Re: RFC: patch to allow lock-free traversal of lists with insertion |
| |
On Wed, 10 Oct 2001, Rusty Russell wrote: > > If noone *holds* a reference, you can remove it "sometime later", > where "sometime later" is (for example) after every CPU has scheduled.
Ehh.. One of those readers can hold on to the thing while waiting for something else to happen.
Looking up a data structure and copying it to user space or similar is _the_ most common operation for any lookup. You MUST NOT free it just because we scheduled away. Scheduling points have zero meaning in real life.
So you'll need a reference count to actually keep such a data structure alive _over_ a schedule. Or all the readers need to copy the data too before they actually start using it. At which point you've made your code a _lot_ slower than the locking version.
Yeah, I can see that your data structure can be made to work by limiting how you can use it ("you must never hold on to a entry over a schedule, reference-counting is a no-no, and you have to stand on your left foot when you look at it sideways").
Linus
- 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/
|  |