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    SubjectRe: [PATCH v6 2/2] Output stall data in debugfs
    On Thu, Aug 11, 2011 at 12:43 PM, Peter Zijlstra <> wrote:
    > zakmagnus seems to bounce, so who am I talking to anyway..
    > On Thu, 2011-08-11 at 21:35 +0200, Peter Zijlstra wrote:
    >> static void show_stall_trace(struct seq_file *f, void *v)
    >> {
    >>         struct stall *s = f->private;
    >>         int i, idx = ACCESS_ONCE(s->idx);
    >>         mutex_lock(&stall_mutex);
    >>         raw_spin_lock(&s->lock[idx]);
    >>         seq_printf(f, "stall: %d\n", s->worst);
    >>         for (i = 0; i < s->trace[idx].nr_entries; i++) {
    >>                 seq_printf(f, "[<%pK>] %pS\n",
    >>                         (void *)s->trace->entries[i],
    >>                         (void *)s->trace->entries[i]);
    >>         }
    >>         raw_spin_unlock(&s->lock[idx]);
    >>         mutex_unlock(&stall_mutex);
    >> }
    >> Yes its racy on s->worst, but who cares (if you do care you can keep a
    >> copy in s->delay[idx] or so). Also, it might be better to not do the
    >> spinlock but simply use an atomic bitop to set an in-use flag, there is
    >> no reason to disable preemption over the seq_printf() loop.
    > That also cures another problem you have, a seq_file buffer is only 1
    > page large, you should be using the seqfile iterator interface and print
    > one line at a time.. now clearly that won't work with preemption
    > disabled either.
    I didn't want to hold on to a lock while the lines were iterated over,
    and instead just dump it in one go. I guess it's not a big deal to do
    that, though. Nonetheless, is one page not enough?
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      Last update: 2011-08-11 21:53    [W:0.025 / U:8.568 seconds]
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