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    SubjectRe: [PATCH] x86: enable preemption in delay

    On Sun, 25 May 2008, Arjan van de Ven wrote:

    > On Sat, 24 May 2008 23:11:20 -0400 (EDT)
    > Steven Rostedt <> wrote:
    > >
    > > In git commit 35d5d08a085c56f153458c3f5d8ce24123617faf, Andrew Morton
    > > placed preempt_disable around the entire delay due to TSC's not
    > > working nicely on SMP. Unfortunately for those that care about
    > > latencies this is devastating! Especially when we have callers to
    > > mdelay(8).
    > we used to have a WARN_ON if mdelay was called while preemptable..
    > maybe we should put that back in?

    That would be a good idea, but that wouldn't solve this issue. The issue
    here is that the mdelay itself disables preemption. The caller had
    preemption enabled.

    The problem was caused by a quick fix by Andrew to handle out of sync
    TSC's for a delay that used TSC's as a counter.

    -- Steve

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