lkml.org 
[lkml]   [2011]   [May]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    SubjectRe: [BUG] "sched: Remove rq->lock from the first half of ttwu()" locks up on ARM
    From
    Date
    On Thu, 2011-05-26 at 19:17 +0200, Peter Zijlstra wrote:
    > On Thu, 2011-05-26 at 19:04 +0200, Oleg Nesterov wrote:
    > > On 05/26, Peter Zijlstra wrote:
    > > >
    > > > @@ -2636,7 +2636,8 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
    > > > * to spin on ->on_cpu if p is current, since that would
    > > > * deadlock.
    > > > */
    > > > - if (p == current) {
    > > > + if (cpu == smp_processor_id()) {
    > > > + p->sched_contributes_to_load = 0;
    > > > ttwu_queue(p, cpu);
    > >
    > > Btw. I do not pretend I really understand se->vruntime, but in this
    > > case we are doing enqueue_task() without ->task_waking(), however we
    > > pass ENQUEUE_WAKING. Is it correct?
    >
    > No its not, that's the thing that I got wrong the first time and caused
    > these pauses.

    We'd end up with something like the below, which isn't too different
    from what I've now got queued.

    It has the extra cpu == smp_processor_id() check, but I'm not sure this
    whole case is worth the trouble. I could go stick some counters in to
    verify how often all this happens I guess.

    ---
    arch/x86/include/asm/system.h | 2 ++
    kernel/sched.c | 14 +++++++++++---
    kernel/sched_debug.c | 7 +++++++
    3 files changed, 20 insertions(+), 3 deletions(-)

    diff --git a/arch/x86/include/asm/system.h b/arch/x86/include/asm/system.h
    index c2ff2a1..2c597e8 100644
    --- a/arch/x86/include/asm/system.h
    +++ b/arch/x86/include/asm/system.h
    @@ -10,6 +10,8 @@
    #include <linux/kernel.h>
    #include <linux/irqflags.h>

    +#define __ARCH_WANT_INTERRUPTS_ON_CTXSW
    +
    /* entries in ARCH_DLINFO: */
    #if defined(CONFIG_IA32_EMULATION) || !defined(CONFIG_X86_64)
    # define AT_VECTOR_SIZE_ARCH 2
    diff --git a/kernel/sched.c b/kernel/sched.c
    index 2d12893..e4f7a9f 100644
    --- a/kernel/sched.c
    +++ b/kernel/sched.c
    @@ -2636,9 +2636,17 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
    * to spin on ->on_cpu if p is current, since that would
    * deadlock.
    */
    - if (p == current) {
    - ttwu_queue(p, cpu);
    - goto stat;
    + if (cpu == smp_processor_id()) {
    + struct rq *rq;
    +
    + rq = __task_rq_lock(p);
    + if (p->on_cpu) {
    + ttwu_activate(rq, p, ENQUEUE_WAKEUP);
    + ttwu_do_wakeup(rq, p, wake_flags);
    + __task_rq_unlock(rq);
    + goto stat;
    + }
    + __task_rq_unlock(rq);
    }
    #endif
    cpu_relax();
    diff --git a/kernel/sched_debug.c b/kernel/sched_debug.c
    index a6710a1..f0ff1de 100644
    --- a/kernel/sched_debug.c
    +++ b/kernel/sched_debug.c
    @@ -332,6 +332,13 @@ static int sched_debug_show(struct seq_file *m, void *v)
    (int)strcspn(init_utsname()->version, " "),
    init_utsname()->version);

    +#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW
    + SEQ_printf(m, "__ARCH_WANT_INTERRUPTS_ON_CTXSW\n");
    +#endif
    +#ifdef __ARCH_WANT_UNLOCKED_CTXSW
    + SEQ_printf(m, "__ARCH_WANT_UNLOCKED_CTXSW\n");
    +#endif
    +
    #define P(x) \
    SEQ_printf(m, "%-40s: %Ld\n", #x, (long long)(x))
    #define PN(x) \



    \
     
     \ /
      Last update: 2011-05-26 19:23    [W:0.026 / U:59.876 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site