linux-kernel - Re: [PATCH 10/12] sched: use {cpu|node}mask pr

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Message-ID: <20150112135034.GC25256@twins.programming.kicks-ass.net>
Date:	Mon, 12 Jan 2015 14:50:34 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH 10/12] sched: use {cpu|node}mask pr_cont and seq output
 functions

On Mon, Jan 12, 2015 at 08:31:45AM -0500, Tejun Heo wrote:
> Hello, Peter.
> 
> On Mon, Dec 15, 2014 at 11:39:15AM +0100, Peter Zijlstra wrote:
> > I would very much prefer something like the below instead..
> > 
> > I'm not a great fan of pr_cont, it makes a mess of things if there's
> > multiple cpus printing bits.
> 
> Yeah, it does sometimes get annoying and bitmaps should be generic
> enough to have support from core printk functions.
> 
> ...
> > --- a/lib/vsprintf.c
> > +++ b/lib/vsprintf.c
> > @@ -27,6 +27,7 @@
> >  #include <linux/uaccess.h>
> >  #include <linux/ioport.h>
> >  #include <linux/dcache.h>
> > +#include <linux/cpumask.h>
> >  #include <net/addrconf.h>
> >  
> >  #include <asm/page.h>		/* for PAGE_SIZE */
> > @@ -1218,6 +1219,7 @@ int kptr_restrict __read_mostly;
> >   *            The maximum supported length is 64 bytes of the input. Consider
> >   *            to use print_hex_dump() for the larger input.
> >   * - 'a' For a phys_addr_t type and its derivative types (passed by reference)
> > + * - 'c' For a cpumask list
> >   *
> >   * Note: The difference between 'S' and 'F' is that on ia64 and ppc64
> >   * function pointers are really function descriptors, which contain a
> > @@ -1335,6 +1337,8 @@ char *pointer(const char *fmt, char *buf
> >  		return dentry_name(buf, end,
> >  				   ((const struct file *)ptr)->f_path.dentry,
> >  				   spec, fmt);
> > +	case 'c':
> > +		return buf + cpulist_scnprintf(buf, end - buf, ptr);
> 
> I think we prolly want something more generic than hard coding cpu and
> node masks into printk.  Prolly something along the line of %*pb so
> that the caller can do something along the line of
> 
>   printk("cpumask: %*pb\n", nr_cpumask_bits, cpumask);
> 
> I'll see if that's actually doable.

See this thread:
  https://lkml.org/lkml/2012/5/9/416
  https://lkml.org/lkml/2012/5/9/353

At the time I couldn't make it work :/
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