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    Subject[PATCH] cleanup sched_yield (sys)call nesting.
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    On Wed, 2009-11-18 at 17:52 +0100, Jean Delvare wrote:
    > On Wed, 18 Nov 2009 17:28:53 +0100, Leon Woestenberg wrote:
    > > On Wed, Nov 18, 2009 at 2:05 AM, Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:
    > > > Our timers are very efficient and some day we will need to make jiffies a
    > > > function and stop the timer ticking for best performance. At that point
    > > > timers are probably the most efficient way to do much of this.
    > >
    > > The problem with I2C bitbanged is the stringent timing, we need a way
    > > to have fine-grained sleeping
    > > mixed with real-time tasks in order to make this work.
    >
    > FWIW, the problem that was initially reported has nothing to do with
    > this. i2c-algo-bit used mdelay() during transactions, not yield().
    > yield() is used only in once place, _between_ transactions attempts.
    > There are no strict timing constraints there.
    >

    I agree that dropping out sched_yield entirely should maybe start by
    deprecating / flagging as a warning in sched_rt.c.

    This is just a minimal cleanup I stumbled across while looking at it -
    to get away from the uglyness of calling into the syscall interface from
    inside the Kernel.

    I'll generate something more substantial for discussion later.

    Subject: clean up chaining in sched_yield()
    From: Sven-Thorsten Dietrich <sdietrich@suse.de>

    The call to sys_sched_yield for in-Kernel is messy.
    and the return code from sys_sched_yield is ignored when called from
    in-kernel.

    Signed-off-by: Sven-Thorsten Dietrich <sdietrich@suse.de>

    diff --git a/kernel/sched.c b/kernel/sched.c
    index 3c11ae0..db2c0f9 100644
    --- a/kernel/sched.c
    +++ b/kernel/sched.c
    @@ -6647,12 +6647,12 @@ SYSCALL_DEFINE3(sched_getaffinity, pid_t, pid, unsigned int, len,
    }

    /**
    - * sys_sched_yield - yield the current processor to other threads.
    + * do_sched_yield - yield the current processor to other threads.
    *
    * This function yields the current CPU to other tasks. If there are no
    * other threads running on this CPU then this function will return.
    */
    -SYSCALL_DEFINE0(sched_yield)
    +static inline void do_sched_yield(void)
    {
    struct rq *rq = this_rq_lock();

    @@ -6669,6 +6669,11 @@ SYSCALL_DEFINE0(sched_yield)
    preempt_enable_no_resched();

    schedule();
    +}
    +
    +SYSCALL_DEFINE0(sched_yield)
    +{
    + do_sched_yield();

    return 0;
    }
    @@ -6746,7 +6751,7 @@ EXPORT_SYMBOL(__cond_resched_softirq);
    void __sched yield(void)
    {
    set_current_state(TASK_RUNNING);
    - sys_sched_yield();
    + do_sched_yield();
    }
    EXPORT_SYMBOL(yield);




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