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[146.241.55.253]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6f2a5856350sm34464696d6.97.2025.04.17.01.29.06 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 17 Apr 2025 01:29:08 -0700 (PDT) Message-ID: <75e10631-00a3-405a-b4d8-96b422ffbe41@redhat.com> Date: Thu, 17 Apr 2025 10:29:05 +0200 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net-next v2 13/18] net/sched: act_mirred: Move the recursion counter struct netdev_xmit To: Sebastian Andrzej Siewior , netdev@vger.kernel.org, linux-rt-devel@lists.linux.dev Cc: "David S. Miller" , Eric Dumazet , Jakub Kicinski , Simon Horman , Thomas Gleixner , Jamal Hadi Salim , Cong Wang , Jiri Pirko References: <20250414160754.503321-1-bigeasy@linutronix.de> <20250414160754.503321-14-bigeasy@linutronix.de> Content-Language: en-US From: Paolo Abeni In-Reply-To: <20250414160754.503321-14-bigeasy@linutronix.de> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/14/25 6:07 PM, Sebastian Andrzej Siewior wrote: > mirred_nest_level is a per-CPU variable and relies on disabled BH for its > locking. Without per-CPU locking in local_bh_disable() on PREEMPT_RT > this data structure requires explicit locking. > > Move mirred_nest_level to struct netdev_xmit as u8, provide wrappers. > > Cc: Jamal Hadi Salim > Cc: Cong Wang > Cc: Jiri Pirko > Signed-off-by: Sebastian Andrzej Siewior > --- > include/linux/netdevice_xmit.h | 3 +++ > net/sched/act_mirred.c | 28 +++++++++++++++++++++++++--- > 2 files changed, 28 insertions(+), 3 deletions(-) > > diff --git a/include/linux/netdevice_xmit.h b/include/linux/netdevice_xmit.h > index 3bbbc1a9860a3..4793ec42b1faa 100644 > --- a/include/linux/netdevice_xmit.h > +++ b/include/linux/netdevice_xmit.h > @@ -11,6 +11,9 @@ struct netdev_xmit { > #if IS_ENABLED(CONFIG_NF_DUP_NETDEV) > u8 nf_dup_skb_recursion; > #endif > +#if IS_ENABLED(CONFIG_NET_ACT_MIRRED) > + u8 sched_mirred_nest; > +#endif > }; How many of such recursion counters do you foresee will be needed? AFAICS this one does not fit the existing hole anymore; the binary layout before this series is: struct netdev_xmit { /* typedef u16 -> __u16 */ short unsigned int recursion; /* 2442 2 */ /* typedef u8 -> __u8 */ unsigned char more; /* 2444 1 */ /* typedef u8 -> __u8 */ unsigned char skip_txqueue; /* 2445 1 */ } net_xmit; /* 2442 4 */ /* XXX 2 bytes hole, try to pack */ and this series already added 2 u8 fields. Since all the recursion counters could be represented with less than 8 bits, perhaps using a bitfield here could be worthy?!? In any case I think we need explicit ack from the sched people. > diff --git a/net/sched/act_mirred.c b/net/sched/act_mirred.c > index 5b38143659249..5f01f567c934d 100644 > --- a/net/sched/act_mirred.c > +++ b/net/sched/act_mirred.c > @@ -30,7 +30,29 @@ static LIST_HEAD(mirred_list); > static DEFINE_SPINLOCK(mirred_list_lock); > > #define MIRRED_NEST_LIMIT 4 > -static DEFINE_PER_CPU(unsigned int, mirred_nest_level); > + > +#ifndef CONFIG_PREEMPT_RT > +static u8 tcf_mirred_nest_level_inc_return(void) > +{ > + return __this_cpu_inc_return(softnet_data.xmit.sched_mirred_nest); > +} > + > +static void tcf_mirred_nest_level_dec(void) > +{ > + __this_cpu_dec(softnet_data.xmit.sched_mirred_nest); > +} > + > +#else > +static u8 tcf_mirred_nest_level_inc_return(void) > +{ > + return current->net_xmit.sched_mirred_nest++; > +} > + > +static void tcf_mirred_nest_level_dec(void) > +{ > + current->net_xmit.sched_mirred_nest--; > +} > +#endif There are already a few of this construct. Perhaps it would be worthy to implement a netdev_xmit() helper returning a ptr to the whole struct and use it to reduce the number of #ifdef Thanks, Paolo