linux-kernel - Re: [PATCH 3/3] blk-throttle: don't parse cgroup path if trace isn't enabled

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Date:	Tue, 10 May 2016 19:33:45 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jeff Moyer <jmoyer@...hat.com>
Cc:	Shaohua Li <shli@...com>, <linux-block@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <axboe@...com>,
	<Kernel-team@...com>
Subject: Re: [PATCH 3/3] blk-throttle: don't parse cgroup path if trace
 isn't enabled

On Tue, 10 May 2016 11:52:15 -0400
Jeff Moyer <jmoyer@...hat.com> wrote:

 
> > +static inline bool blk_trace_note_message_enabled(struct request_queue *q)
> > +{
> > +	struct blk_trace *bt = q->blk_trace;
> > +	if (likely(!bt))
> > +		return false;
> > +	return bt->act_mask & BLK_TC_NOTIFY;  
> 
> Do we want to return !!(bt->act_mask & BLK_TC_NOTIFY)?

The return type is bool. I would think that gcc would be smart enough
to make the conversion.

To check, I compiled the following function:

bool testbool(int x)
{
        return x & 1<<3;
}

and the result was:


0000000000000000 <testbool>:
   0:   55                      push   %rbp
   1:   48 89 e5                mov    %rsp,%rbp
   4:   89 7d fc                mov    %edi,-0x4(%rbp)
   7:   8b 45 fc                mov    -0x4(%rbp),%eax
   a:   83 e0 08                and    $0x8,%eax
   d:   85 c0                   test   %eax,%eax
   f:   0f 95 c0                setne  %al
  12:   5d                      pop    %rbp
  13:   c3                      retq   

I get the same by adding !!(x & 1<<3)

Looks like it does the conversion.

-- Steve