linux-kernel - Re: [PATCH v13 12/32] x86,fs/resctrl: Support binary fixed point event counters

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Message-ID: <aRIYZOm6ZtpQFr4m@agluck-desk3>
Date: Mon, 10 Nov 2025 08:52:52 -0800
From: "Luck, Tony" <tony.luck@...el.com>
To: Dave Martin <Dave.Martin@....com>
CC: Fenghua Yu <fenghuay@...dia.com>, Reinette Chatre
	<reinette.chatre@...el.com>, Maciej Wieczor-Retman
	<maciej.wieczor-retman@...el.com>, Peter Newman <peternewman@...gle.com>,
	James Morse <james.morse@....com>, Babu Moger <babu.moger@....com>, "Drew
 Fustini" <dfustini@...libre.com>, Chen Yu <yu.c.chen@...el.com>,
	<x86@...nel.org>, <linux-kernel@...r.kernel.org>, <patches@...ts.linux.dev>
Subject: Re: [PATCH v13 12/32] x86,fs/resctrl: Support binary fixed point
 event counters

On Wed, Nov 05, 2025 at 02:42:18PM +0000, Dave Martin wrote:
> > +static void print_event_value(struct seq_file *m, unsigned int binary_bits, u64 val)
> > +{
> > +	unsigned long long frac;
> > +	char buf[10];
> 
> In place of the magic number 10, how about
> decplaces[MAX_BINARY_BITS] + 1 ?
> 
> (I think the compiler should accept that as an initialiser if the array
> is const.)

The compiler (gcc 15.2.1) accepts without any warnings. But generates
different code.

sparse complains:
fs/resctrl/ctrlmondata.c:640:45: warning: Variable length array is used.

I may change the hard coded constant to 21 (guaranteed to be big enough
for a "long long" plus terminating NUL byte.)

-Tony