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Date: Wed, 8 Nov 2017 16:57:41 +0100
From: Jiri Olsa <jolsa@redhat.com>
To: Milind Chabbi <chabbi.milind@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
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        Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>,
        Jin Yao <yao.jin@linux.intel.com>
Subject: Re: [PATCH] perf/core: fast breakpoint modification via
 _IOC_MODIFY_BREAKPOINT
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On Wed, Nov 08, 2017 at 07:51:10AM -0800, Milind Chabbi wrote:
> 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?

I don't know ;-)

jirka