Re: [PATCH RFC] netfilter: cacheline aligning in struct netns_ct

[Zhouyi Zhou]

Thanks Jesper and David for reviewing and replying.

Great commitment of Jesper for moving above three hlist_nulls_heads to
percpu structure. Sorry to miss the newest advances in nf-next.

And arbitrarily cache-line aligning structure members is not a good idea
for large cache lines.

Still I have an idea that could we pack the seldom changed members
 (nf_ct_proto included) to a structure and we allocated it from a
cache aligned slub when the structure "net" is initialized.


Zhouyi

On Wed, Mar 12, 2014 at 5:36 PM, David Laight <David.Laight@xxxxxxxxxx> wrote:
> From: Zhouyi Zhou
>> not frequently changing components should share same cachelines
>>
>> Signed-off-by: Zhouyi Zhou <yizhouzhou@xxxxxxxxx>
>> ---
>>  include/net/netns/conntrack.h |   12 ++++++++----
>>  1 file changed, 8 insertions(+), 4 deletions(-)
>>
>> diff --git a/include/net/netns/conntrack.h b/include/net/netns/conntrack.h
>> index fbcc7fa..69d2d58 100644
>> --- a/include/net/netns/conntrack.h
>> +++ b/include/net/netns/conntrack.h
>> @@ -65,6 +65,12 @@ struct nf_ip_net {
>>  struct netns_ct {
>>       atomic_t                count;
>>       unsigned int            expect_count;
>> +     struct hlist_nulls_head unconfirmed;
>> +     struct hlist_nulls_head dying;
>> +     struct hlist_nulls_head tmpl;
>> +
>> +     /*  not frequently changing components should share same cachelines */
>> +     struct nf_ip_net        nf_ct_proto ____cacheline_aligned_in_smp;
>
> I'm not sure this has the effect you are trying to achieve.
> Adding an __attribute__((aligned(n))) to a structure member not only
> adds padding before the member, but also pads the member to a multiple
> of the specified size.
>
> With large cache lines you probably want neither.
> IIRC one of the ppc systems has something like 256 byte cache lines
> (and if it doesn't now, it might have soon).
> So arbitrarily cache-line aligning structure members may not be a good idea.
>
> In any case reducing the number of cache lines accessed, and the number
> dirtied is probably more important than putting 'readonly' data in its
> own cache lines.
>
>         David
>
>
>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/