On Mon, 11 Jun 2007, Eric Sesterhenn / Snakebyte wrote:
>
> +unlikely | 40969931| 6228144 __slab_free()@:mm/slub.c@1606
> +unlikely | 47198075| 0 __slab_free()@:mm/slub.c@1599
> -likely | 0| 47198075 slab_free()@:mm/slub.c@1660
> +unlikely | 47280864| 0 __slab_alloc()@:mm/slub.c@1475
> +unlikely | 26857| 0 new_slab()@:mm/slub.c@1107
> +unlikely | 47280864| 0 slab_alloc()@:mm/slub.c@1557
>
> three of the unlikely cases are caused by "if (unlikely(SlabDebug(page)))"
> if SLUB_DEBUG is turned off, it really is unlikely, since SlabDebug()
> always returns 0, if SLUB_DEBUG is turned on it is likely (not sure if there are
> cases where it can return 0) therefore it makes sense to change this
> to likely for the SLUB_DEBUG case.
>
> The following patch changes the SlabDebug() functions to defines, so gcc
> can easily optimize the if away entirely and changes the unlikely() to a
> likely().
>
> Remaining problem is, that if likely/unlikely profiling is turned on,
> gcc does not optimize away a likely(0), and they still show up in the
> stats... guess heisenbug is involved in this :-)
There is a fundamental misunderstanding here to think that SLUB_DEBUG
would enable debugging. Not true. Debugging is enabled by booting with
"slub_debug".
It is true that SlabDebug() is always false if !CONFIG_SLUB_DEBUG. That is
only the case for embedded systems that want to conserve memory.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
