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    SubjectRe: [RFC PATCH 1/5] x86: introduce preemption disable prefix
    On Fri, Oct 19, 2018 at 1:22 AM Peter Zijlstra <peterz@infradead.org> wrote:
    >
    > On Thu, Oct 18, 2018 at 10:00:53PM -0700, Alexei Starovoitov wrote:
    > > >
    > > > >
    > > > > Another example is __BPF_PROG_RUN_ARRAY(), which also uses
    > > > > preempt_enable_no_resched().
    > > >
    > > > Alexei, I think this code is just wrong.
    > >
    > > why 'just wrong' ?
    >
    > Because you lost a preemption point, this is a no-no.
    >
    > >
    > > > Do you know why it uses
    > > > preempt_enable_no_resched()?
    > >
    > > dont recall precisely.
    > > we could be preemptable at the point where macro is called.
    > > I think the goal of no_resched was to avoid adding scheduling points
    > > where they didn't exist before just because a prog ran for few nsec.
    > > May be Daniel or Roman remember.
    >
    > No, you did the exact opposite, where there previously was a preemption,
    > you just ate it. The band saw didn't get stopped in time, you loose your
    > hand etc..

    Let me do few experiments then.
    We will fix it up.

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