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From: Ingo Molnar on 22 Aug 2008 00:50

* Paul E. McKenney <paulmck(a)linux.vnet.ibm.com> wrote:

> +#define MAX_RCU_LEVELS 3
> +#if NR_CPUS <= CONFIG_RCU_FANOUT
> +#define NUM_RCU_LEVELS 1
> +#define NUM_RCU_LEVEL_1 1
> +#define NUM_RCU_LEVEL_2 NR_CPUS
> +#define NUM_RCU_LEVEL_3 0
> +#define NUM_RCU_LEVEL_4 0
> +#define NUM_RCU_NODES NUM_RCU_LEVEL_1
> +#elif NR_CPUS <= CONFIG_RCU_FANOUT * CONFIG_RCU_FANOUT
> +#define NUM_RCU_LEVELS 2
> +#define NUM_RCU_LEVEL_1 1
> +#define NUM_RCU_LEVEL_2 \
> + (((NR_CPUS) + (CONFIG_RCU_FANOUT) - 1) / (CONFIG_RCU_FANOUT))
> +#define NUM_RCU_LEVEL_3 NR_CPUS
> +#define NUM_RCU_LEVEL_4 0
> +#define NUM_RCU_NODES \
> + ((NUM_RCU_LEVEL_1) + (NUM_RCU_LEVEL_2))
> +#elif NR_CPUS <= CONFIG_RCU_FANOUT * CONFIG_RCU_FANOUT * CONFIG_RCU_FANOUT
> +#define NUM_RCU_LEVELS 3
> +#define RCU_FANOUT_SQ ((CONFIG_RCU_FANOUT) * (CONFIG_RCU_FANOUT))
> +#define NUM_RCU_LEVEL_1 1
> +#define NUM_RCU_LEVEL_2 \
> + (((NR_CPUS) + (RCU_FANOUT_SQ) - 1) / (RCU_FANOUT_SQ))
> +#define NUM_RCU_LEVEL_3 \
> + ((NR_CPUS) + (CONFIG_RCU_FANOUT) - 1) / (CONFIG_RCU_FANOUT)
> +#define NUM_RCU_LEVEL_4 NR_CPUS
> +#define NUM_RCU_NODES \
> + ((NUM_RCU_LEVEL_1) + \
> + (NUM_RCU_LEVEL_2) + \
> + (NUM_RCU_LEVEL_3))
> +#else
> +#error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
> +#endif

just a quick stylistic suggestion: if feasible then such sizing ugliness
should be hidden in a Kconfig file. (if Kconfig is capable enough for
this that is)

Ingo
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From: Paul E. McKenney on 22 Aug 2008 09:50
On Fri, Aug 22, 2008 at 06:37:15AM +0200, Ingo Molnar wrote:
>
> * Paul E. McKenney <paulmck(a)linux.vnet.ibm.com> wrote:
>
> > +#define MAX_RCU_LEVELS 3
> > +#if NR_CPUS <= CONFIG_RCU_FANOUT
> > +#define NUM_RCU_LEVELS 1
> > +#define NUM_RCU_LEVEL_1 1
> > +#define NUM_RCU_LEVEL_2 NR_CPUS
> > +#define NUM_RCU_LEVEL_3 0
> > +#define NUM_RCU_LEVEL_4 0
> > +#define NUM_RCU_NODES NUM_RCU_LEVEL_1
> > +#elif NR_CPUS <= CONFIG_RCU_FANOUT * CONFIG_RCU_FANOUT
> > +#define NUM_RCU_LEVELS 2
> > +#define NUM_RCU_LEVEL_1 1
> > +#define NUM_RCU_LEVEL_2 \
> > + (((NR_CPUS) + (CONFIG_RCU_FANOUT) - 1) / (CONFIG_RCU_FANOUT))
> > +#define NUM_RCU_LEVEL_3 NR_CPUS
> > +#define NUM_RCU_LEVEL_4 0
> > +#define NUM_RCU_NODES \
> > + ((NUM_RCU_LEVEL_1) + (NUM_RCU_LEVEL_2))
> > +#elif NR_CPUS <= CONFIG_RCU_FANOUT * CONFIG_RCU_FANOUT * CONFIG_RCU_FANOUT
> > +#define NUM_RCU_LEVELS 3
> > +#define RCU_FANOUT_SQ ((CONFIG_RCU_FANOUT) * (CONFIG_RCU_FANOUT))
> > +#define NUM_RCU_LEVEL_1 1
> > +#define NUM_RCU_LEVEL_2 \
> > + (((NR_CPUS) + (RCU_FANOUT_SQ) - 1) / (RCU_FANOUT_SQ))
> > +#define NUM_RCU_LEVEL_3 \
> > + ((NR_CPUS) + (CONFIG_RCU_FANOUT) - 1) / (CONFIG_RCU_FANOUT)
> > +#define NUM_RCU_LEVEL_4 NR_CPUS
> > +#define NUM_RCU_NODES \
> > + ((NUM_RCU_LEVEL_1) + \
> > + (NUM_RCU_LEVEL_2) + \
> > + (NUM_RCU_LEVEL_3))
> > +#else
> > +#error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
> > +#endif
>
> just a quick stylistic suggestion: if feasible then such sizing ugliness
> should be hidden in a Kconfig file. (if Kconfig is capable enough for
> this that is)

I have no idea if Kconfig can do it, but I will check.

Thanx, Paul
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From: Paul E. McKenney on 22 Aug 2008 13:30
On Fri, Aug 22, 2008 at 06:47:20AM -0700, Paul E. McKenney wrote:
> On Fri, Aug 22, 2008 at 06:37:15AM +0200, Ingo Molnar wrote:
> >
> > * Paul E. McKenney <paulmck(a)linux.vnet.ibm.com> wrote:
> >
> > > +#define MAX_RCU_LEVELS 3
> > > +#if NR_CPUS <= CONFIG_RCU_FANOUT
> > > +#define NUM_RCU_LEVELS 1
> > > +#define NUM_RCU_LEVEL_1 1
> > > +#define NUM_RCU_LEVEL_2 NR_CPUS
> > > +#define NUM_RCU_LEVEL_3 0
> > > +#define NUM_RCU_LEVEL_4 0
> > > +#define NUM_RCU_NODES NUM_RCU_LEVEL_1
> > > +#elif NR_CPUS <= CONFIG_RCU_FANOUT * CONFIG_RCU_FANOUT
> > > +#define NUM_RCU_LEVELS 2
> > > +#define NUM_RCU_LEVEL_1 1
> > > +#define NUM_RCU_LEVEL_2 \
> > > + (((NR_CPUS) + (CONFIG_RCU_FANOUT) - 1) / (CONFIG_RCU_FANOUT))
> > > +#define NUM_RCU_LEVEL_3 NR_CPUS
> > > +#define NUM_RCU_LEVEL_4 0
> > > +#define NUM_RCU_NODES \
> > > + ((NUM_RCU_LEVEL_1) + (NUM_RCU_LEVEL_2))
> > > +#elif NR_CPUS <= CONFIG_RCU_FANOUT * CONFIG_RCU_FANOUT * CONFIG_RCU_FANOUT
> > > +#define NUM_RCU_LEVELS 3
> > > +#define RCU_FANOUT_SQ ((CONFIG_RCU_FANOUT) * (CONFIG_RCU_FANOUT))
> > > +#define NUM_RCU_LEVEL_1 1
> > > +#define NUM_RCU_LEVEL_2 \
> > > + (((NR_CPUS) + (RCU_FANOUT_SQ) - 1) / (RCU_FANOUT_SQ))
> > > +#define NUM_RCU_LEVEL_3 \
> > > + ((NR_CPUS) + (CONFIG_RCU_FANOUT) - 1) / (CONFIG_RCU_FANOUT)
> > > +#define NUM_RCU_LEVEL_4 NR_CPUS
> > > +#define NUM_RCU_NODES \
> > > + ((NUM_RCU_LEVEL_1) + \
> > > + (NUM_RCU_LEVEL_2) + \
> > > + (NUM_RCU_LEVEL_3))
> > > +#else
> > > +#error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
> > > +#endif
> >
> > just a quick stylistic suggestion: if feasible then such sizing ugliness
> > should be hidden in a Kconfig file. (if Kconfig is capable enough for
> > this that is)
>
> I have no idea if Kconfig can do it, but I will check.

OK, Kconfig does not currently support arithmetic, based on zconf.y:

expr: symbol { $$ = expr_alloc_symbol($1); }
| symbol T_EQUAL symbol { $$ = expr_alloc_comp(E_EQUAL, $1, $3); }
| symbol T_UNEQUAL symbol { $$ = expr_alloc_comp(E_UNEQUAL, $1, $3); }
| T_OPEN_PAREN expr T_CLOSE_PAREN { $$ = $2; }
| T_NOT expr { $$ = expr_alloc_one(E_NOT, $2); }
| expr T_OR expr { $$ = expr_alloc_two(E_OR, $1, $3); }
| expr T_AND expr { $$ = expr_alloc_two(E_AND, $1, $3); }
;

All we currently get is basic comparison and logical operators. It would
not be all -that- hard to add general arithmetic (famous last words),
but when I tried mapping out what the sizing code would look like in
such an augmented Kconfig, it was even uglier than the above.

So I took a hard look at the current mess, and prettied it as shown below.
Is this a sufficient improvement?

Another alternative I am considering is moving this to a separate
include file.

Thoughts?

Thanx, Paul

#define MAX_RCU_LEVELS 3
#define RCU_FANOUT (CONFIG_RCU_FANOUT)
#define RCU_FANOUT_SQ (RCU_FANOUT * RCU_FANOUT)
#define RCU_FANOUT_CUBE (RCU_FANOUT_SQ * RCU_FANOUT)

#if (NR_CPUS) <= RCU_FANOUT
# define NUM_RCU_LVLS 1
# define NUM_RCU_LVL_0 1
# define NUM_RCU_LVL_1 (NR_CPUS)
# define NUM_RCU_LVL_2 0
# define NUM_RCU_LVL_3 0
#elif (NR_CPUS) <= RCU_FANOUT_SQ
# define NUM_RCU_LVLS 2
# define NUM_RCU_LVL_0 1
# define NUM_RCU_LVL_1 (((NR_CPUS) + RCU_FANOUT - 1) / RCU_FANOUT)
# define NUM_RCU_LVL_2 (NR_CPUS)
# define NUM_RCU_LVL_3 0
#elif (NR_CPUS) <= RCU_FANOUT_CUBE
# define NUM_RCU_LVLS 3
# define NUM_RCU_LVL_0 1
# define NUM_RCU_LVL_1 (((NR_CPUS) + RCU_FANOUT_SQ - 1) / RCU_FANOUT_SQ)
# define NUM_RCU_LVL_2 (((NR_CPUS) + (RCU_FANOUT) - 1) / (RCU_FANOUT))
# define NUM_RCU_LVL_3 NR_CPUS
#else
# error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
#endif /* #if (NR_CPUS) <= RCU_FANOUT */

#define RCU_SUM (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2 + NUM_RCU_LVL_3)
#define NUM_RCU_NODES (RCU_SUM - NR_CPUS)
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From: Josh Triplett on 22 Aug 2008 14:20
On Fri, 2008-08-22 at 10:22 -0700, Paul E. McKenney wrote:
> On Fri, Aug 22, 2008 at 06:47:20AM -0700, Paul E. McKenney wrote:
> > On Fri, Aug 22, 2008 at 06:37:15AM +0200, Ingo Molnar wrote:
> > >
> > > * Paul E. McKenney <paulmck(a)linux.vnet.ibm.com> wrote:
> > >
> > > > +#define MAX_RCU_LEVELS 3
> > > > +#if NR_CPUS <= CONFIG_RCU_FANOUT
> > > > +#define NUM_RCU_LEVELS 1
> > > > +#define NUM_RCU_LEVEL_1 1
> > > > +#define NUM_RCU_LEVEL_2 NR_CPUS
> > > > +#define NUM_RCU_LEVEL_3 0
> > > > +#define NUM_RCU_LEVEL_4 0
> > > > +#define NUM_RCU_NODES NUM_RCU_LEVEL_1
> > > > +#elif NR_CPUS <= CONFIG_RCU_FANOUT * CONFIG_RCU_FANOUT
> > > > +#define NUM_RCU_LEVELS 2
> > > > +#define NUM_RCU_LEVEL_1 1
> > > > +#define NUM_RCU_LEVEL_2 \
> > > > + (((NR_CPUS) + (CONFIG_RCU_FANOUT) - 1) / (CONFIG_RCU_FANOUT))
> > > > +#define NUM_RCU_LEVEL_3 NR_CPUS
> > > > +#define NUM_RCU_LEVEL_4 0
> > > > +#define NUM_RCU_NODES \
> > > > + ((NUM_RCU_LEVEL_1) + (NUM_RCU_LEVEL_2))
> > > > +#elif NR_CPUS <= CONFIG_RCU_FANOUT * CONFIG_RCU_FANOUT * CONFIG_RCU_FANOUT
> > > > +#define NUM_RCU_LEVELS 3
> > > > +#define RCU_FANOUT_SQ ((CONFIG_RCU_FANOUT) * (CONFIG_RCU_FANOUT))
> > > > +#define NUM_RCU_LEVEL_1 1
> > > > +#define NUM_RCU_LEVEL_2 \
> > > > + (((NR_CPUS) + (RCU_FANOUT_SQ) - 1) / (RCU_FANOUT_SQ))
> > > > +#define NUM_RCU_LEVEL_3 \
> > > > + ((NR_CPUS) + (CONFIG_RCU_FANOUT) - 1) / (CONFIG_RCU_FANOUT)
> > > > +#define NUM_RCU_LEVEL_4 NR_CPUS
> > > > +#define NUM_RCU_NODES \
> > > > + ((NUM_RCU_LEVEL_1) + \
> > > > + (NUM_RCU_LEVEL_2) + \
> > > > + (NUM_RCU_LEVEL_3))
> > > > +#else
> > > > +#error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
> > > > +#endif
> > >
> > > just a quick stylistic suggestion: if feasible then such sizing ugliness
> > > should be hidden in a Kconfig file. (if Kconfig is capable enough for
> > > this that is)
> >
> > I have no idea if Kconfig can do it, but I will check.
>
> OK, Kconfig does not currently support arithmetic, based on zconf.y:
>
> expr: symbol { $$ = expr_alloc_symbol($1); }
> | symbol T_EQUAL symbol { $$ = expr_alloc_comp(E_EQUAL, $1, $3); }
> | symbol T_UNEQUAL symbol { $$ = expr_alloc_comp(E_UNEQUAL, $1, $3); }
> | T_OPEN_PAREN expr T_CLOSE_PAREN { $$ = $2; }
> | T_NOT expr { $$ = expr_alloc_one(E_NOT, $2); }
> | expr T_OR expr { $$ = expr_alloc_two(E_OR, $1, $3); }
> | expr T_AND expr { $$ = expr_alloc_two(E_AND, $1, $3); }
> ;
>
> All we currently get is basic comparison and logical operators. It would
> not be all -that- hard to add general arithmetic (famous last words),
> but when I tried mapping out what the sizing code would look like in
> such an augmented Kconfig, it was even uglier than the above.

Makes sense.

> So I took a hard look at the current mess, and prettied it as shown below.
> Is this a sufficient improvement?

Looks significantly improved.

> Another alternative I am considering is moving this to a separate
> include file.

I personally don't think that would help. The revised version seems
fine.

> #define MAX_RCU_LEVELS 3
> #define RCU_FANOUT (CONFIG_RCU_FANOUT)
> #define RCU_FANOUT_SQ (RCU_FANOUT * RCU_FANOUT)
> #define RCU_FANOUT_CUBE (RCU_FANOUT_SQ * RCU_FANOUT)
>
> #if (NR_CPUS) <= RCU_FANOUT
> # define NUM_RCU_LVLS 1
> # define NUM_RCU_LVL_0 1
> # define NUM_RCU_LVL_1 (NR_CPUS)
> # define NUM_RCU_LVL_2 0
> # define NUM_RCU_LVL_3 0
> #elif (NR_CPUS) <= RCU_FANOUT_SQ
> # define NUM_RCU_LVLS 2
> # define NUM_RCU_LVL_0 1
> # define NUM_RCU_LVL_1 (((NR_CPUS) + RCU_FANOUT - 1) / RCU_FANOUT)
> # define NUM_RCU_LVL_2 (NR_CPUS)
> # define NUM_RCU_LVL_3 0
> #elif (NR_CPUS) <= RCU_FANOUT_CUBE
> # define NUM_RCU_LVLS 3
> # define NUM_RCU_LVL_0 1
> # define NUM_RCU_LVL_1 (((NR_CPUS) + RCU_FANOUT_SQ - 1) / RCU_FANOUT_SQ)
> # define NUM_RCU_LVL_2 (((NR_CPUS) + (RCU_FANOUT) - 1) / (RCU_FANOUT))
> # define NUM_RCU_LVL_3 NR_CPUS
> #else
> # error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
> #endif /* #if (NR_CPUS) <= RCU_FANOUT */
>
> #define RCU_SUM (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2 + NUM_RCU_LVL_3)
> #define NUM_RCU_NODES (RCU_SUM - NR_CPUS)

- Josh Triplett


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From: Ingo Molnar on 23 Aug 2008 12:20

* Paul E. McKenney <paulmck(a)linux.vnet.ibm.com> wrote:

> Is this a sufficient improvement?

yeah - looks much better. This was the block that meets the eye for the
first time in the patch so it stuck out.

just one more small pet peeve of mine: please use vertical alignment too
to improve readability. Instead of:

> #define MAX_RCU_LEVELS 3
> #define RCU_FANOUT (CONFIG_RCU_FANOUT)
> #define RCU_FANOUT_SQ (RCU_FANOUT * RCU_FANOUT)
> #define RCU_FANOUT_CUBE (RCU_FANOUT_SQ * RCU_FANOUT)

this looks a bit more structured IMO:

> #define MAX_RCU_LEVELS 3
> #define RCU_FANOUT (CONFIG_RCU_FANOUT)
> #define RCU_FANOUT_SQ (RCU_FANOUT * RCU_FANOUT)
> #define RCU_FANOUT_CUBE (RCU_FANOUT_SQ * RCU_FANOUT)

maybe even this:

> #if (NR_CPUS) <= RCU_FANOUT
> # define NUM_RCU_LVLS 1
> # define NUM_RCU_LVL_0 1
> # define NUM_RCU_LVL_1 (NR_CPUS)
> # define NUM_RCU_LVL_2 0
> # define NUM_RCU_LVL_3 0
> #elif (NR_CPUS) <= RCU_FANOUT_SQ
> # define NUM_RCU_LVLS 2
> # define NUM_RCU_LVL_0 1
> # define NUM_RCU_LVL_1 (((NR_CPUS) + RCU_FANOUT - 1) / RCU_FANOUT)
> # define NUM_RCU_LVL_2 (NR_CPUS)
> # define NUM_RCU_LVL_3 0
> #elif (NR_CPUS) <= RCU_FANOUT_CUBE
> # define NUM_RCU_LVLS 3
> # define NUM_RCU_LVL_0 1
> # define NUM_RCU_LVL_1 (((NR_CPUS) + RCU_FANOUT_SQ - 1) / RCU_FANOUT_SQ)
> # define NUM_RCU_LVL_2 (((NR_CPUS) + (RCU_FANOUT) - 1) / (RCU_FANOUT))
> # define NUM_RCU_LVL_3 NR_CPUS
> #else
> # error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
> #endif /* #if (NR_CPUS) <= RCU_FANOUT */

but no strong feelings on that one. (maybe inserting a space at the
right places helps too, no need for a full tab)

Ingo
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