Re: [PATCH] perf/core: fast breakpoint modification via _IOC_MODIFY_BREAKPOINT

Milind Chabbi
2017-11-08T15:51:28Z

On Wed, Nov 8, 2017 at 7:12 AM, Jiri Olsa <jolsa@redhat.com> wrote:

> > I am not able to fully understand your concern.
> > Can you point to a code file and line related to your observation?
> > The patch is modeled after the existing modify_user_hw_breakpoint() function
> > present in events/hw_breakpoint.c; don't you see this problem in that code?
>
> the reserve_bp_slot/release_bp_slot functions manage
> counts for current breakpoints based on its type
>
> those counts are cumulated in here:
> static DEFINE_PER_CPU(struct bp_cpuinfo, bp_cpuinfo[TYPE_MAX]);
>
> you allow to change the breakpoint type, so I'd expect
> to see some code that release slot count for old type
> and take new one (if it's available)
>
> jirka

Why is this not a concern for modify_user_hw_breakpoint() function?