linux-kernel - Re: [PATCH 1/3] x86: modify show_shared_cpu_map in intel

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Message-ID: <47FBD915.7020809@sgi.com>
Date:	Tue, 08 Apr 2008 13:44:05 -0700
From:	Mike Travis <travis@....com>
To:	Bert Wesarg <bert.wesarg@...glemail.com>
CC:	Ingo Molnar <mingo@...e.hu>, Paul Jackson <pj@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] x86: modify show_shared_cpu_map in intel_cacheinfo
 v3

Bert Wesarg wrote:
> On Tue, Apr 8, 2008 at 8:43 PM, Mike Travis <travis@....com> wrote:
>>  --- linux-2.6.x86.sched.orig/arch/x86/kernel/cpu/intel_cacheinfo.c
>>  +++ linux-2.6.x86.sched/arch/x86/kernel/cpu/intel_cacheinfo.c
>>  @@ -591,20 +591,34 @@ static ssize_t show_size(struct _cpuid4_
>>         return sprintf (buf, "%luK\n", this_leaf->size / 1024);
>>   }
>>
>>  -static ssize_t show_shared_cpu_map(struct _cpuid4_info *this_leaf, char *buf)
>>  +static ssize_t show_shared_cpu_map_func(struct _cpuid4_info *this_leaf,
>>  +                                       int type, char *buf)
> I don't know if this is more efficient or better or cleaner, but how
> about to pass the function pointer (ie. cpulist_scnprintf or
> cpumap_scnprintf)? You safe at least one condition.
> 
>>  +               n = type?
>>  +                       cpulist_scnprintf(buf, len-2, *mask):
>>  +                       cpumask_scnprintf(buf, len-2, *mask);
> 
> Thanks.
> Bert

I have to subvert the cpumask interface a bit, but the resultant
code size is about 7 instructions smaller.

static ssize_t show_shared_cpu_map_func(struct _cpuid4_info *this_leaf,
		int (*cpumap_func)(char *, int, const cpumask_t *, int),
		char *buf)
{
	ptrdiff_t len = PTR_ALIGN(buf + PAGE_SIZE - 1, PAGE_SIZE) - buf;
	int n = 0;

	if (len > 1) {
		cpumask_t *mask = &this_leaf->shared_cpu_map;
		n = cpumap_func(buf, len-2, mask, NR_CPUS);
		buf[n++] = '\n';
		buf[n] = '\0';
	}
	return n;
}

static inline ssize_t show_shared_cpu_map(struct _cpuid4_info *leaf, char *buf)
{
	return show_shared_cpu_map_func(leaf, &__cpumask_scnprintf, buf);
}

static inline ssize_t show_shared_cpu_list(struct _cpuid4_info *leaf, char *buf)
{
	return show_shared_cpu_map_func(leaf, &__cpulist_scnprintf, buf);
}

Btw, you were asking about how to determine NR_CPUS.  Here's one way:

root@...ton:~# cat /sys/devices/system/cpu/online
0-2,4-7
root@...ton:~# cat /sys/devices/system/cpu/possible
0-511
root@...ton:~# cat /sys/devices/system/cpu/present
0-7
root@...ton:~# cat /sys/devices/system/cpu/system
0-4095

Thanks,
Mike
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