Re: [PATCH 1/3] perf/x86/amd: AMD support for bp_len > HW_BREAKPOINT_LEN_8

Oleg Nesterov
2013-12-10T16:19:01Z

On 12/10, Frederic Weisbecker wrote:
>
> On Wed, Oct 02, 2013 at 11:11:06AM -0500, suravee.suthikulpanit@amd.com wrote:
> > @@ -279,7 +260,16 @@ static int arch_build_bp_info(struct perf_event *bp)
> > }
> >
> > /* Len */
> > + info->mask = 0;
> > +
> > switch (bp->attr.bp_len) {
> > + default:
> > + if (!is_power_of_2(bp->attr.bp_len))
> > + return -EINVAL;
> > + if (!cpu_has_bpext)
> > + return -EOPNOTSUPP;
> > + info->mask = bp->attr.bp_len - 1;
> > + /* fall through */
>
> So, that's perhaps just personal preference but having the default on
> top of the switch makes things very confusing. Can't we put the above
> in the end of the switch instead?

Then "fall through" won't work ;)

> > @@ -314,11 +303,11 @@ int arch_validate_hwbkpt_settings(struct perf_event *bp)
> > if (ret)
> > return ret;
> >
> > - ret = -EINVAL;
> > -
> > switch (info->len) {
> > case X86_BREAKPOINT_LEN_1:
> > align = 0;
> > + if (info->mask)
> > + align = info->mask;
>
> Confused, I thought mask is set only when length is above 8?

Yes. But we need the info->len for hw anyway. if mask != 0 then
len == X86_BREAKPOINT_LEN_1 and it is still used by encode_dr7().
Note that it is not the length in bytes, it is the magic x86 code.

->bp_len is the length.

Oleg.