On Thu, 15 Jan 2015 16:40:32 +0900
Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> wrote:
[...]
>
> I saw roughly 5% win in a fast-path loop over kmem_cache_alloc/free
> in CONFIG_PREEMPT. (14.821 ns -> 14.049 ns)
>
> Below is the result of Christoph's slab_test reported by
> Jesper Dangaard Brouer.
>
[...]
Acked-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
> Acked-by: Christoph Lameter <cl@xxxxxxxxx>
> Tested-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> ---
> mm/slub.c | 35 +++++++++++++++++++++++------------
> 1 file changed, 23 insertions(+), 12 deletions(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index fe376fe..ceee1d7 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2398,13 +2398,24 @@ redo:
[...]
> */
> - preempt_disable();
> - c = this_cpu_ptr(s->cpu_slab);
> + do {
> + tid = this_cpu_read(s->cpu_slab->tid);
> + c = this_cpu_ptr(s->cpu_slab);
> + } while (IS_ENABLED(CONFIG_PREEMPT) && unlikely(tid != c->tid));
> +
> + /*
> + * Irqless object alloc/free alogorithm used here depends on sequence
Spelling of algorithm contains a typo ^^
> + * of fetching cpu_slab's data. tid should be fetched before anything
> + * on c to guarantee that object and page associated with previous tid
> + * won't be used with current tid. If we fetch tid first, object and
> + * page could be one associated with next tid and our alloc/free
> + * request will be failed. In this case, we will retry. So, no problem.
> + */
> + barrier();
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Sr. Network Kernel Developer at Red Hat
Author of http://www.iptv-analyzer.org
LinkedIn: http://www.linkedin.com/in/brouer
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