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SubjectRe: [patch 01/11] Introducing generic hardware breakpoint handler interfaces

* Alan Stern <stern@rowland.harvard.edu> wrote:

> On Tue, 10 Mar 2009, Ingo Molnar wrote:
>
> > * prasad@linux.vnet.ibm.com <prasad@linux.vnet.ibm.com> wrote:
> >
> >
> > > +static u8 tprio[HB_NUM]; /* Thread bp max priorities */
> > > +LIST_HEAD(kernel_bps); /* Kernel breakpoint list */
> > > +static LIST_HEAD(thread_list); /* thread_hw_breakpoint list */
> > > +DEFINE_PER_CPU(struct cpu_hw_breakpoint, cpu_bp);
>
> If nobody minds, I'll answer some of these questions on
> Prasad's behalf because they address parts of the code that
> were written before he took over the project.
>
> > hm, why do we need the whole 'priority' mechanism? It seems
> > very over-designed to me.
>
> This was done at Roland McGrath's express request. We should
> see what he has to say about it.
>
> > The likelyhood of both user-space and kernel-space to use
> > hw-breakpoints is very low to begin with. And if they use
> > them, the likelyhood of there being more than 4 debugregs
> > required in the same context is even lower.
>
> Not all architectures have 4 debug registers. Most have only
> one.
>
> > If that happens we shouldnt try to be too smart about them -
> > just override user-space ones with kernel space ones and
> > that's it. No explicit priorities are needed.
>
> Roland really did not want it done this way.

Well i guess i'll have to wait for Roland's reply then.

Ingo


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