Re: pserialize(9) vs. TAILQ

[Dennis Ferguson <dennis.c.ferguson%gmail.com@localhost>]

On 25 Nov, 2014, at 00:56 , Taylor R Campbell <campbell+netbsd-tech-kern%mumble.net@localhost> wrote:
>   My confusion came from that I thought memory ordering of load is more
>   flexible in general.  I also didn't quite understand "dependent-load".
>   I have been only reading NetBSD kernel code to learn memory ordering;
>   and I believe, nothing in the tree utilize this topologycal
>   "dependent-load".  I may be missing something though.
> 
> We do have at least one use of nontrivial data-dependent loads
> in-tree, in pcq(9), as Dennis noted.

More than that, I think.  If I'm not mistaken there are also examples in

    sys/kern/kern_descrip.c
    sys/kern/kern_tc.c
    sys/kern/subr_ipi.c
    sys/kern/vfs_cache.c

When there is code which fills in a structure, followed by a membar_producer(),
followed by an assignment to a pointer to point at the structure, it is very
unlikely that there will be barriers in the places where the pointer is dereferenced.

Dennis Ferguson