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    SubjectRe: 2.6.21-rc3-mm1 RSDL results
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    Con Kolivas <kernel@kolivas.org> writes:

    > On Friday 09 March 2007 18:53, Matt Mackall wrote:
    ...
    >>
    >> With a single non-parallel make running (all in cache, mind you), the
    >> system kicks up into just about 100% CPU usage at full speed. Desktop
    >> spinning becomes between 10x to 100x slower (from ~30fps to < 1fps).
    >> Galeon scrolling pauses for as much as a second. Mouse movement pauses
    >> for as much as a second. Typing in terminals lags noticeably.
    >>
    >> This is not the expected behavior of a fair, low-latency scheduler.
    >
    > No indeed it does not sound right at all to me either. Last time I encountered
    > something like this we traced it and hit sched_yield calls somewhere in the
    > graphic pipeline. So first question is, how does mainline perform with the
    > same testcase, and second question is umm whatever it is that is slow is
    > there a way to trace it to see if it yields?

    Matt, some 3d drivers are known to do sched_yield() behind user's back,

    (notably dri radeon ones, grep for sched_yield:
    http://webcvs.freedesktop.org/mesa/Mesa/src/mesa/drivers/dri/r200/r200_ioctl.c?revision=1.37&view=markup
    http://webcvs.freedesktop.org/mesa/Mesa/src/mesa/drivers/dri/r300/radeon_ioctl.c?revision=1.14&view=markup)

    thus absolutely killing any desktop interactivity whatsoever.

    If you see sched_yield() when stracing any 3d program, I suggest you
    to try this bruteforce workaround, which works fine for me,
    disable sched_yield():


    kernel/sched.c | 9 +++++++--
    1 file changed, 7 insertions(+), 2 deletions(-)

    Index: linux/kernel/sched.c
    ===================================================================
    --- linux.orig/kernel/sched.c
    +++ linux/kernel/sched.c
    @@ -4285,7 +4285,7 @@ asmlinkage long sys_sched_getaffinity(pi
    * This function yields the current CPU by dropping the priority of current
    * to the lowest priority.
    */
    -asmlinkage long sys_sched_yield(void)
    +static long sys_sched_yield1(void)
    {
    struct rq *rq = this_rq_lock();
    struct task_struct *p = current;
    @@ -4312,6 +4312,11 @@ asmlinkage long sys_sched_yield(void)
    return 0;
    }

    +asmlinkage long sys_sched_yield(void)
    +{
    + return 0;
    +}
    +
    static void __cond_resched(void)
    {
    #ifdef CONFIG_DEBUG_SPINLOCK_SLEEP
    @@ -4395,7 +4400,7 @@ EXPORT_SYMBOL(cond_resched_softirq);
    void __sched yield(void)
    {
    set_current_state(TASK_RUNNING);
    - sys_sched_yield();
    + sys_sched_yield1();
    }
    EXPORT_SYMBOL(yield);

    -
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      Last update: 2007-03-09 10:11    [W:0.036 / U:32.892 seconds]
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