From: Jamal Hadi Salim <jhs@mojatatu•com>
To: Eric Dumazet <eric.dumazet@gmail•com>,
Cong Wang <xiyou.wangcong@gmail•com>
Cc: netdev <netdev@vger•kernel.org>,
John Fastabend <john.fastabend@gmail•com>,
Kevin Athey <kda@google•com>, Xiaotian Pei <xiaotian@google•com>
Subject: Re: [RFC net-next] net: sched: do not acquire qdisc spinlock in qdisc/class stats dump
Date: Sun, 22 May 2016 12:35:07 -0400 [thread overview]
Message-ID: <5741DFBB.8040003@mojatatu.com> (raw)
In-Reply-To: <1463723432.18194.274.camel@edumazet-glaptop3.roam.corp.google.com>
On 16-05-20 01:50 AM, Eric Dumazet wrote:
> It wont be inaccurate (no drift), as the writers hold the qdisc
> spinlock.
>
> It it the same with say IP/TCP SNMP counters :
>
> When an incoming frame is handled, it might change many SNMP counters,
> but an SNMP agent might fetch the whole set of SNMP values in the middle
> of the changes.
>
> IpInReceives
> IpInDelivers
> TcpInSegs
> IpExtInOctets
> IpExtInNoECTPkts
> ...
>
> The only 'problem' can be a off-by-one (or off-by-bytes-in-the-packet)
> transient error, that all SNMP agents are normally handling just fine.
>
I think qdisc stats being off by a bit are ok - hence the rcu
suggestion. I would have problems with action stats being off
(where they are used for billing).
cheers,
jamal
next prev parent reply other threads:[~2016-05-22 16:47 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-19 12:35 [RFC net-next] net: sched: do not acquire qdisc spinlock in qdisc/class stats dump Eric Dumazet
2016-05-19 16:08 ` Alexei Starovoitov
2016-05-19 17:02 ` Eric Dumazet
2016-05-20 1:50 ` Cong Wang
2016-05-20 2:45 ` Eric Dumazet
2016-05-20 5:23 ` Cong Wang
2016-05-20 5:50 ` Eric Dumazet
2016-05-22 16:35 ` Jamal Hadi Salim [this message]
2016-05-20 12:44 ` Eric Dumazet
2016-05-20 13:01 ` Eric Dumazet
2016-05-20 13:09 ` Eric Dumazet
2016-05-20 23:38 ` David Miller
2016-05-22 16:30 ` Jamal Hadi Salim
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