2016-09-14 19:28:40

by Eric Biggers

[permalink] [raw]

Subject: [PATCH] blockgroup_lock.h: simplify definition of NR_BG_LOCKS

---

We can use ilog2() to more easily produce the desired NR_BG_LOCKS. This
works because ilog2() is evaluated at compile-time when its argument is
a compile-time constant.

I did not change the chosen NR_BG_LOCKS values.

Signed-off-by: Eric Biggers <[email protected]>
---
include/linux/blockgroup_lock.h | 22 ++--------------------
1 file changed, 2 insertions(+), 20 deletions(-)

diff --git a/include/linux/blockgroup_lock.h b/include/linux/blockgroup_lock.h
index 61b583d..225bdb7 100644
--- a/include/linux/blockgroup_lock.h
+++ b/include/linux/blockgroup_lock.h
@@ -10,28 +10,10 @@
#include <linux/cache.h>

#ifdef CONFIG_SMP
-
-/*
- * We want a power-of-two. Is there a better way than this?
- */
-
-#if NR_CPUS >= 32
-#define NR_BG_LOCKS 128
-#elif NR_CPUS >= 16
-#define NR_BG_LOCKS 64
-#elif NR_CPUS >= 8
-#define NR_BG_LOCKS 32
-#elif NR_CPUS >= 4
-#define NR_BG_LOCKS 16
-#elif NR_CPUS >= 2
-#define NR_BG_LOCKS 8
+#define NR_BG_LOCKS (4 << ilog2(NR_CPUS < 32 ? NR_CPUS : 32))
#else
-#define NR_BG_LOCKS 4
-#endif
-
-#else /* CONFIG_SMP */
#define NR_BG_LOCKS 1
-#endif /* CONFIG_SMP */
+#endif

struct bgl_lock {
spinlock_t lock;
--
2.8.0.rc3.226.g39d4020

2016-09-14 21:09:30

by Andreas Dilger

[permalink] [raw]

Subject: Re: [PATCH] blockgroup_lock.h: simplify definition of NR_BG_LOCKS

---

On Sep 14, 2016, at 1:28 PM, Eric Biggers <[email protected]> wrote:
>
> We can use ilog2() to more easily produce the desired NR_BG_LOCKS. This
> works because ilog2() is evaluated at compile-time when its argument is
> a compile-time constant.
>
> I did not change the chosen NR_BG_LOCKS values.
>
> Signed-off-by: Eric Biggers <[email protected]>

Reviewed-by: Andreas Dilger <[email protected]>

> ---
> include/linux/blockgroup_lock.h | 22 ++--------------------
> 1 file changed, 2 insertions(+), 20 deletions(-)
>
> diff --git a/include/linux/blockgroup_lock.h b/include/linux/blockgroup_lock.h
> index 61b583d..225bdb7 100644
> --- a/include/linux/blockgroup_lock.h
> +++ b/include/linux/blockgroup_lock.h
> @@ -10,28 +10,10 @@
> #include <linux/cache.h>
>
> #ifdef CONFIG_SMP
> -
> -/*
> - * We want a power-of-two. Is there a better way than this?
> - */
> -
> -#if NR_CPUS >= 32
> -#define NR_BG_LOCKS 128
> -#elif NR_CPUS >= 16
> -#define NR_BG_LOCKS 64
> -#elif NR_CPUS >= 8
> -#define NR_BG_LOCKS 32
> -#elif NR_CPUS >= 4
> -#define NR_BG_LOCKS 16
> -#elif NR_CPUS >= 2
> -#define NR_BG_LOCKS 8
> +#define NR_BG_LOCKS (4 << ilog2(NR_CPUS < 32 ? NR_CPUS : 32))
> #else
> -#define NR_BG_LOCKS 4
> -#endif
> -
> -#else /* CONFIG_SMP */
> #define NR_BG_LOCKS 1
> -#endif /* CONFIG_SMP */
> +#endif
>
> struct bgl_lock {
> spinlock_t lock;
> --
> 2.8.0.rc3.226.g39d4020
>


Cheers, Andreas

---

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2016-09-15 22:30:08

by Theodore Ts'o

[permalink] [raw]

Subject: Re: [PATCH] blockgroup_lock.h: simplify definition of NR_BG_LOCKS

---

On Wed, Sep 14, 2016 at 03:09:30PM -0600, Andreas Dilger wrote:
> On Sep 14, 2016, at 1:28 PM, Eric Biggers <[email protected]> wrote:
> >
> > We can use ilog2() to more easily produce the desired NR_BG_LOCKS. This
> > works because ilog2() is evaluated at compile-time when its argument is
> > a compile-time constant.
> >
> > I did not change the chosen NR_BG_LOCKS values.
> >
> > Signed-off-by: Eric Biggers <[email protected]>
>
> Reviewed-by: Andreas Dilger <[email protected]>

Applied, thanks.

- Ted