linux-kernel - RE: [PATCH v5 8/8] selftests/resctrl: Adjust effective L3 cache size when SNC enabled

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Message-ID: <SJ1PR11MB60838CA98A341F59260BDE18FCE6A@SJ1PR11MB6083.namprd11.prod.outlook.com>
Date:   Wed, 30 Aug 2023 15:43:05 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     "Wieczor-Retman, Maciej" <maciej.wieczor-retman@...el.com>
CC:     "Yu, Fenghua" <fenghua.yu@...el.com>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        Peter Newman <peternewman@...gle.com>,
        "Jonathan Corbet" <corbet@....net>,
        Shuah Khan <skhan@...uxfoundation.org>,
        "x86@...nel.org" <x86@...nel.org>,
        Shaopeng Tan <tan.shaopeng@...itsu.com>,
        James Morse <james.morse@....com>,
        Jamie Iles <quic_jiles@...cinc.com>,
        "Babu Moger" <babu.moger@....com>,
        Randy Dunlap <rdunlap@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "patches@...ts.linux.dev" <patches@...ts.linux.dev>
Subject: RE: [PATCH v5 8/8] selftests/resctrl: Adjust effective L3 cache size
 when SNC enabled

> >+static int count_sys_bitmap_bits(char *name)
> >+{
> >+    FILE *fp = fopen(name, "r");
> >+    int count = 0, c;
> >+
> >+    if (!fp)
> >+            return 0;
> >+
> >+    while ((c = fgetc(fp)) != EOF) {
> >+            if (!isxdigit(c))
> >+                    continue;
> >+            switch (c) {
> >+            case 'f':
> >+                    count++;
> >+            case '7': case 'b': case 'd': case 'e':
> >+                    count++;
> >+            case '3': case '5': case '6': case '9': case 'a': case 'c':
> >+                    count++;
> >+            case '1': case '2': case '4': case '8':
> >+                    count++;
> >+            }
> >+    }
> >+    fclose(fp);
> >+
> >+    return count;
> >+}
> >+
>
> The resctrl selftest has a function for counting bits, could it be used
> here instead of the switch statement like this for example?
>
> count = count_bits(c);
>
> Or is there some reason this wouldn't be a good fit here?

Thanks for looking at my patch.

That count_bits() function is doing so with input from an "unsigned long"
argument.  My function is parsing the string result from a sysfs file which
might look like this:

$ cat shared_cpu_map
0000,00000fff,ffffff00,0000000f,ffffffff

To use count_bits() I'd have to use something like strtol() on each of the
comma separated fields first to convert from ascii strings to binary
values to feed into count_bits().

-Tony