Messages in this thread | | | Date | Thu, 26 Jul 2007 10:45:56 -0700 | From | "David J. Wilder" <> | Subject | Re: [Question] Hooks for scheduler tracing (CFS) |
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> I guess they might have to switch to such an asynchronous delivery > system if they want to do this properly. Simply put, your polling > solution is exactly what I do, but I check a flag set by the writer > instead of waking up the readers unconditionally. > > Mathieu >
Ingo's solution could call waitqueue_active() inside wakeup_readers() to determine if there are waiters. Right?
> >> Ingo >> >> -------------------------------------> >> Subject: relay: fix timer madness >> From: Ingo Molnar <mingo@elte.hu> >> >> remove timer calls (!!!) from deep within the tracing infrastructure. >> This was totally bogus code that can cause lockups and worse. >> Poll the buffer every 2 jiffies for now. >> >> Signed-off-by: Ingo Molnar <mingo@elte.hu> >> --- >> kernel/relay.c | 14 +++++--------- >> 1 file changed, 5 insertions(+), 9 deletions(-) >> >> Index: linux-rt-rebase.q/kernel/relay.c >> =================================================================== >> --- linux-rt-rebase.q.orig/kernel/relay.c >> +++ linux-rt-rebase.q/kernel/relay.c >> @@ -319,6 +319,10 @@ static void wakeup_readers(unsigned long >> { >> struct rchan_buf *buf = (struct rchan_buf *)data; >> wake_up_interruptible(&buf->read_wait); >> + /* >> + * Stupid polling for now: >> + */ >> + mod_timer(&buf->timer, jiffies + 1); >> } >> >> /** >> @@ -336,6 +340,7 @@ static void __relay_reset(struct rchan_b >> init_waitqueue_head(&buf->read_wait); >> kref_init(&buf->kref); >> setup_timer(&buf->timer, wakeup_readers, (unsigned long)buf); >> + mod_timer(&buf->timer, jiffies + 1); >> } else >> del_timer_sync(&buf->timer); >> >> @@ -604,15 +609,6 @@ size_t relay_switch_subbuf(struct rchan_ >> buf->subbufs_produced++; >> buf->dentry->d_inode->i_size += buf->chan->subbuf_size - >> buf->padding[old_subbuf]; >> - smp_mb(); >> - if (waitqueue_active(&buf->read_wait)) >> - /* >> - * Calling wake_up_interruptible() from here >> - * will deadlock if we happen to be logging >> - * from the scheduler (trying to re-grab >> - * rq->lock), so defer it. >> - */ >> - __mod_timer(&buf->timer, jiffies + 1); >> } >> >> old = buf->data; >> > >
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