# Re: \[PATCH 1/3\] printk: Release console\_sem after logbuf\_lock

- From: Peter Zijlstra \<peterz@infradead.org\>
- Date: 2011-06-10 12:42:23 
- List: linux-fbdev
- Page: https://ratatoskr.run/linux-fbdev/2011/06/3727846
- Thread: https://ratatoskr.run/linux-fbdev/2011/06/3727840/t.md

```text
On Fri, 2011-06-10 at 14:34 +0200, Ingo Molnar wrote:
> * Peter Zijlstra [ref] wrote:
> 
> > thinking that that would have my printk stmts appear on both the 
> > fbcon as well as the serial line. But they fail to appear on the 
> > latency tracer (current max was 165us waking an idle cpu).
> 
> Have you removed this bit:
> 
>                 spin_unlock(&logbuf_lock);
>                 stop_critical_timings();        /* don't trace print latency */
>                 call_console_drivers(_con_start, _log_end);
>                 start_critical_timings();
>                 local_irq_restore(flags);
> 
> which hides the latencies from the latency tracer?

it shouldn't those flags come from spin_lock_irqsave(), which already
has IRQs disabled, so the restore shouldn't re-enable them.

Hmm,. that might actually already be true for mainline too, yeah, looks
like we call vprintk()->console_unlock() with IRQs-disabled.

Hohumm..
```