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    Subject[tip:core/urgent] rcutorture: Occasionally delay readers enough to make RCU force_quiescent_state
    Commit-ID:  f4a82a059aea43947d4f37dba9da1782d11caece
    Gitweb: http://git.kernel.org/tip/f4a82a059aea43947d4f37dba9da1782d11caece
    Author: Josh Triplett <josh@joshtriplett.org>
    AuthorDate: Tue, 8 Sep 2009 15:54:35 -0700
    Committer: Ingo Molnar <mingo@elte.hu>
    CommitDate: Sat, 12 Sep 2009 09:47:07 +0200

    rcutorture: Occasionally delay readers enough to make RCU force_quiescent_state

    rcutorture already delays readers, but never for long enough to
    make RCU force a quiescent state. Add an occasional delay of
    50ms.

    Signed-off-by: Josh Triplett <josh@joshtriplett.org>
    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Acked-by: Steven Rostedt <rostedt@goodmis.org>
    Cc: laijs@cn.fujitsu.com
    Cc: dipankar@in.ibm.com
    Cc: akpm@linux-foundation.org
    Cc: mathieu.desnoyers@polymtl.ca
    Cc: josht@linux.vnet.ibm.com
    Cc: dvhltc@us.ibm.com
    Cc: niv@us.ibm.com
    Cc: peterz@infradead.org
    LKML-Reference: <12524504772607-git-send-email->
    Signed-off-by: Ingo Molnar <mingo@elte.hu>


    ---
    kernel/rcutorture.c | 15 +++++++++------
    1 files changed, 9 insertions(+), 6 deletions(-)

    diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
    index b33db53..328a825 100644
    --- a/kernel/rcutorture.c
    +++ b/kernel/rcutorture.c
    @@ -281,14 +281,17 @@ static int rcu_torture_read_lock(void) __acquires(RCU)

    static void rcu_read_delay(struct rcu_random_state *rrsp)
    {
    - long delay;
    - const long longdelay = 200;
    + const unsigned long shortdelay_us = 200;
    + const unsigned long longdelay_ms = 50;

    - /* We want there to be long-running readers, but not all the time. */
    + /* We want a short delay sometimes to make a reader delay the grace
    + * period, and we want a long delay occasionally to trigger
    + * force_quiescent_state. */

    - delay = rcu_random(rrsp) % (nrealreaders * 2 * longdelay);
    - if (!delay)
    - udelay(longdelay);
    + if (!(rcu_random(rrsp) % (nrealreaders * 2000 * longdelay_ms)))
    + mdelay(longdelay_ms);
    + if (!(rcu_random(rrsp) % (nrealreaders * 2 * shortdelay_us)))
    + udelay(shortdelay_us);
    }

    static void rcu_torture_read_unlock(int idx) __releases(RCU)

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