linux-kernel - Re: [RFC PATCH v2 06/20] tracing/filters: Optimise scalar vs cpumask filtering when the user mask is a single CPU

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Message-ID: <b7cf996a-f443-402c-8e13-c5f25a964184@kadam.mountain>
Date:   Mon, 31 Jul 2023 19:03:04 +0300
From:   Dan Carpenter <dan.carpenter@...aro.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Valentin Schneider <vschneid@...hat.com>,
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Subject: Re: [RFC PATCH v2 06/20] tracing/filters: Optimise scalar vs cpumask
 filtering when the user mask is a single CPU

On Mon, Jul 31, 2023 at 11:54:53AM -0400, Steven Rostedt wrote:
> On Mon, 31 Jul 2023 15:07:52 +0300
> Dan Carpenter <dan.carpenter@...aro.org> wrote:
> 
> > On Sat, Jul 29, 2023 at 03:55:47PM -0400, Steven Rostedt wrote:
> > > > @@ -1761,6 +1761,11 @@ static int parse_pred(const char *str, void *data,
> > > >  				FILTER_PRED_FN_CPUMASK;
> > > >  		} else if (field->filter_type == FILTER_CPU) {
> > > >  			pred->fn_num = FILTER_PRED_FN_CPU_CPUMASK;
> > > > +		} else if (single) {
> > > > +			pred->op = pred->op == OP_BAND ? OP_EQ : pred->op;  
> > > 
> > > Nit, the above can be written as:
> > > 
> > > 			pred->op = pret->op != OP_BAND ? : OP_EQ;
> > >   
> > 
> > Heh.  Those are not equivalent.  The right way to write this is:
> 
> You mean because of my typo?

No, I hadn't seen the s/pred/pret/ typo.  Your code does:

	if (pred->op != OP_BAND)
		pred->op = true;
	else
		pred->op OP_EQ;

Realy we should probably trigger a static checker warning any time
someone does a compare operations as part of a "x = comparison ?: bar;
Years ago, someone asked me to do that with regards to error codes like:

	return ret < 0 ?: -EINVAL;

but I don't remember the results.

regards,
dan carpenter