On Tue, 28 Jun 2005, Paul E. McKenney wrote:
> On i386, writes are ordered. So if CPU1 sees the callback, it is
> guaranteed to also see the data.
Yes indeed, i was certain that i missed something ;)
> However, you do have a good point -- weakly ordered CPUs would need to
> have an explicit memory barrier. This might well already be taken care
> of by the memory barriers in the locking primitives used by the up()
> operation invoked at the end of oprofile_start(), but I did not check
> all the possible ways that these functions can be called.
I agree, that usage looks safe.
> Given that set_nmi_callback isn't invoked all that often, seems like
> it might be preferable to insert an smp_wmb() at the beginning of
> set_nmi_callback(), so that it reads as follows:
>
> void set_nmi_callback(nmi_callback_t callback)
> {
> smp_wmb();
> nmi_callback = callback;
> }
>
> Thoughts?
Andrew (rightly) tends to howls whenever someone adds a memory barrier
without a comment ;) So if we were to make that change, how about the
following accompanying comment;
"smp_wmb ensures that all data dependencies for the callback are posted
and callback is ready for execution"
Thanks for elaborating, the examples certainly do help clarify usage.
Zwane
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
