From: Daniel Borkmann <daniel@iogearbox•net>
To: Eric Dumazet <eric.dumazet@gmail•com>
Cc: davem@davemloft•net, jhs@mojatatu•com, ast@plumgrid•com,
edumazet@google•com, netdev@vger•kernel.org
Subject: Re: [PATCH net-next] net: use jump label patching for ingress qdisc in __netif_receive_skb_core
Date: Sat, 11 Apr 2015 00:34:46 +0200 [thread overview]
Message-ID: <55285006.9040805@iogearbox.net> (raw)
In-Reply-To: <1428705014.25985.331.camel@edumazet-glaptop2.roam.corp.google.com>
On 04/11/2015 12:30 AM, Eric Dumazet wrote:
> On Fri, 2015-04-10 at 23:07 +0200, Daniel Borkmann wrote:
>> Even if we make use of classifier and actions from the egress
>> path, we're going into handle_ing() executing additional code
>> on a per-packet cost for ingress qdisc, just to realize that
>> nothing is attached on ingress.
>>
>> Instead, this can just be blinded out as a no-op entirely with
>> the use of a static key. On input fast-path, we already make
>> use of static keys in various places, e.g. skb time stamping,
>> in RPS, etc. It makes sense to not waste time when we're assured
>> that no ingress qdisc is attached anywhere.
>>
>> Enabling/disabling of that code path is being done via two
>> helpers, namely net_{inc,dec}_ingress_queue(), that are being
>> invoked under RTNL mutex when a ingress qdisc is being either
>> initialized or destructed.
>>
>> Signed-off-by: Daniel Borkmann <daniel@iogearbox•net>
>
> My concern about jump labels is they add a conditional on arches where
> CONFIG_JUMP_LABEL=n
>
> They look great on x86, but not sure about say MIPS.
>
> The cost of the extra conditional on MIPS was OK to avoid a call to
> __net_timestamp(), but maybe not to avoid a simple dereference ?
Thanks for the review! I could change that test into a macro and
test if CONFIG_JUMP_LABEL=n to make that if (1) effectively.
next prev parent reply other threads:[~2015-04-10 22:34 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-10 21:07 [PATCH net-next] net: use jump label patching for ingress qdisc in __netif_receive_skb_core Daniel Borkmann
2015-04-10 22:30 ` Eric Dumazet
2015-04-10 22:34 ` Daniel Borkmann [this message]
2015-04-10 22:40 ` Alexei Starovoitov
2015-04-11 1:14 ` Cong Wang
2015-04-11 1:41 ` Alexei Starovoitov
2015-04-11 15:40 ` Alexei Starovoitov
2015-04-13 17:35 ` David Miller
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