linux-kernel - Re: [PATCH net-next 1/3] net: sched: cls_api: add skip

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Date: Fri, 16 Feb 2024 10:35:40 +0200
From: Vlad Buslov <vladbu@...dia.com>
To: Asbjørn Sloth Tønnesen <ast@...erby.net>
CC: Jamal Hadi Salim <jhs@...atatu.com>, Cong Wang <xiyou.wangcong@...il.com>,
	Jiri Pirko <jiri@...nulli.us>, Daniel Borkmann <daniel@...earbox.net>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>, <llu@...erby.dk>,
	Marcelo Ricardo Leitner <mleitner@...hat.com>
Subject: Re: [PATCH net-next 1/3] net: sched: cls_api: add skip_sw counter

On Thu 15 Feb 2024 at 23:34, Asbjørn Sloth Tønnesen <ast@...erby.net> wrote:
> Hi Jamal,
>
> Thank you for the review.
>
> On 2/15/24 17:39, Jamal Hadi Salim wrote:
>> +Cc Vlad and Marcelo..
>> On Thu, Feb 15, 2024 at 11:06 AM Asbjørn Sloth Tønnesen <ast@...erby.net>
>> wrote:
>>>
>>> Maintain a count of skip_sw filters.
>>>
>>> This counter is protected by the cb_lock, and is updated
>>> at the same time as offloadcnt.
>>>
>>> Signed-off-by: Asbjørn Sloth Tønnesen <ast@...erby.net>
>>> ---
>>>   include/net/sch_generic.h | 1 +
>>>   net/sched/cls_api.c       | 4 ++++
>>>   2 files changed, 5 insertions(+)
>>>
>>> diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
>>> index 934fdb977551..46a63d1818a0 100644
>>> --- a/include/net/sch_generic.h
>>> +++ b/include/net/sch_generic.h
>>> @@ -476,6 +476,7 @@ struct tcf_block {
>>>          struct flow_block flow_block;
>>>          struct list_head owner_list;
>>>          bool keep_dst;
>>> +       atomic_t skipswcnt; /* Number of skip_sw filters */
>>>          atomic_t offloadcnt; /* Number of oddloaded filters */
>> For your use case is skipswcnt ever going to be any different than offloadcnt?
>
> No, we only use skip_sw filters, since we only use TC as a control path to
> install skip_sw rules into hardware.
>
> AFAICT offloadcnt is the sum of skip_sw filters, and filters with no flags which
> have implicitly been offloaded.
>
> The reason that I didn't just use offloadcnt, is that I'm not sure if it is
> acceptable to treat implicitly offloaded rules without skip_sw, as if they were
> explicitly skip_sw. It sounds reasonable, given that the filters without skip_* flags
> shouldn't really care.

It is not acceptable since there are valid use-cases where packets need
to match sw filters that are supposedly also in-hw. For example, filters
with tunnel_key set action during neighbor update event.

>
> I tried to only trigger the TC bypass, in the cases that I was absolutely sure would
> be safe as a first step.
>
>
>> cheers,
>> jamal
>> 
>>>          unsigned int nooffloaddevcnt; /* Number of devs unable to do offload */
>>>          unsigned int lockeddevcnt; /* Number of devs that require rtnl lock. */
>>> diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
>>> index ca5676b2668e..397c3d29659c 100644
>>> --- a/net/sched/cls_api.c
>>> +++ b/net/sched/cls_api.c
>>> @@ -3483,6 +3483,8 @@ static void tcf_block_offload_inc(struct tcf_block *block, u32 *flags)
>>>          if (*flags & TCA_CLS_FLAGS_IN_HW)
>>>                  return;
>>>          *flags |= TCA_CLS_FLAGS_IN_HW;
>>> +       if (tc_skip_sw(*flags))
>>> +               atomic_inc(&block->skipswcnt);
>>>          atomic_inc(&block->offloadcnt);
>>>   }
>>>
>>> @@ -3491,6 +3493,8 @@ static void tcf_block_offload_dec(struct tcf_block *block, u32 *flags)
>>>          if (!(*flags & TCA_CLS_FLAGS_IN_HW))
>>>                  return;
>>>          *flags &= ~TCA_CLS_FLAGS_IN_HW;
>>> +       if (tc_skip_sw(*flags))
>>> +               atomic_dec(&block->skipswcnt);
>>>          atomic_dec(&block->offloadcnt);
>>>   }
>>>
>>> --
>>> 2.43.0
>>>