Messages in this thread | | | Date | Tue, 12 Jan 2010 04:39:32 +0100 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 14/26] trace: Convert various locks to raw_spinlock |
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On Mon, Jan 11, 2010 at 10:26:44PM +0100, John Kacur wrote: > Convert locks that cannot sleep in preempt-rt to raw_spinlocks. > > See also: 87654a70523a8c5baadcbbc07d80cbae8f912837 > > Signed-off-by: John Kacur <jkacur@redhat.com> > --- > kernel/trace/ring_buffer.c | 52 +++++++++++++++++++++--------------------- > kernel/trace/trace.c | 10 ++++---- > kernel/trace/trace_irqsoff.c | 6 ++-- > 3 files changed, 34 insertions(+), 34 deletions(-) > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index 2326b04..ffaddc5 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c > @@ -422,7 +422,7 @@ int ring_buffer_print_page_header(struct trace_seq *s) > struct ring_buffer_per_cpu { > int cpu; > struct ring_buffer *buffer; > - spinlock_t reader_lock; /* serialize readers */ > + raw_spinlock_t reader_lock; /* serialize readers */
Why this one? This is a reader lock, not taken in any tracing fast path places. Why should it never sleep in rt, it's taken by a reader of the ring buffer, which doesn't seem to me involved in any critical work.
I may be wrong though, better wait for Steve to correct me if needed.
In any case, the changelog needs more details about the individual purpose of this patch.
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index 0df1b0f..0c6bbcb 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -258,7 +258,7 @@ unsigned long trace_flags = TRACE_ITER_PRINT_PARENT | TRACE_ITER_PRINTK | > TRACE_ITER_GRAPH_TIME; > > static int trace_stop_count; > -static DEFINE_SPINLOCK(tracing_start_lock); > +static DEFINE_RAW_SPINLOCK(tracing_start_lock);
Same here. I don't understand why this should never sleep in -rt. This is not a critical lock. It is taken in rare and not critical places, mostly in reader places when we open/release a trace file and also in tracing selftests.
> diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c > index 2974bc7..60ba58e 100644 > --- a/kernel/trace/trace_irqsoff.c > +++ b/kernel/trace/trace_irqsoff.c > @@ -23,7 +23,7 @@ static int tracer_enabled __read_mostly; > > static DEFINE_PER_CPU(int, tracing_cpu); > > -static DEFINE_SPINLOCK(max_trace_lock); > +static DEFINE_RAW_SPINLOCK(max_trace_lock);
But there yeah, it does seem necessary as it is involved in irqsoff tracing fastpath.
This needs a comment though.
Thanks.
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