[lkml]   [2007]   [Aug]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH] SLUB use cmpxchg_local
* Christoph Lameter ( wrote:
> On Tue, 21 Aug 2007, Mathieu Desnoyers wrote:
> > Are you running a UP or SMP kernel ? If you run a UP kernel, the
> > cmpxchg_local and cmpxchg are identical.
> UP.
> > Oh, and if you run your tests at boot time, the alternatives code may
> > have removed the lock prefix, therefore making cmpxchg and cmpxchg_local
> > exactly the same.
> Tests were run at boot time.
> That still does not explain kmalloc not showing improvements.

Hrm, weird.. because it should. Here are the numbers I posted

The measurements I get (in cycles):
enable interrupts (STI) disable interrupts (CLI) local CMPXCHG
IA32 (P4) 112 82 26
x86_64 AMD64 125 102 19

So both AMD64 and IA32 should be improved.

So why those improvements are not shown in your test ? A few possible

- Do you have any CONFIG_DEBUG_* options activated ? smp_processor_id()
may end up being more expensive in these cases.
- Rounding error.. you seem to round at 0.1ms, but I keep the values in
cycles. The times that you get (1.1ms) seems strangely higher than
mine, which are under 1000 cycles on a 3GHz system (less than 333ns).
I guess there is both a ms - ns error there and/or not enough
precision in your numbers.


Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2007-08-22 02:05    [W:0.131 / U:0.568 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site