Re: [PATCH net-next v2 2/9] net: sched: act_sample: add action cookie to sample
From: Ilya Maximets
Date: Tue Jun 18 2024 - 07:11:31 EST
On 6/18/24 09:38, Adrián Moreno wrote:
> On Mon, Jun 17, 2024 at 12:00:04PM GMT, Ilya Maximets wrote:
>> On 6/3/24 20:56, Adrian Moreno wrote:
>>> If the action has a user_cookie, pass it along to the sample so it can
>>> be easily identified.
>>>
>>> Signed-off-by: Adrian Moreno <amorenoz@xxxxxxxxxx>
>>> ---
>>> net/sched/act_sample.c | 12 ++++++++++++
>>> 1 file changed, 12 insertions(+)
>>>
>>> diff --git a/net/sched/act_sample.c b/net/sched/act_sample.c
>>> index a69b53d54039..5c3f86ec964a 100644
>>> --- a/net/sched/act_sample.c
>>> +++ b/net/sched/act_sample.c
>>> @@ -165,9 +165,11 @@ TC_INDIRECT_SCOPE int tcf_sample_act(struct sk_buff *skb,
>>> const struct tc_action *a,
>>> struct tcf_result *res)
>>> {
>>> + u8 cookie_data[TC_COOKIE_MAX_SIZE] = {};
>>
>> Is it necessary to initialize these 16 bytes on every call?
>> Might be expensive. We're passing the data length around,
>> so the uninitialized parts should not be accessed.
>>
>
> They "should" not, indeed. I was just trying to be extra careful.
> Are you worried TC_COOKIE_MAX_SIZE could grow or the cycles needed to
> clear the current 16 bytes?
I'm assuming that any extra cycles spent per packet are undesirable,
so should be avoided, if possible. Even if we save 1-2 cycles per
packet, it's a lot when we talk about millions of packets per second.
In this particular case, it seems, we do not sacrifice anything, so
it's just a couple of cycles back for free.
Best regards, Ilya Maximets.