From: Paolo Abeni <pabeni@redhat•com>
To: Cong Wang <xiyou.wangcong@gmail•com>
Cc: Linux Kernel Network Developers <netdev@vger•kernel.org>,
Jamal Hadi Salim <jhs@mojatatu•com>,
Jiri Pirko <jiri@resnulli•us>,
"David S. Miller" <davem@davemloft•net>
Subject: Re: [RFC PATCH] net_sched: bulk free tcf_block
Date: Fri, 01 Dec 2017 12:05:07 +0100 [thread overview]
Message-ID: <1512126307.3155.26.camel@redhat.com> (raw)
In-Reply-To: <CAM_iQpWt5B0q5GE_gs-772H+dWUDJxJHG5vy-i6V9SyThyCihg@mail.gmail.com>
On Thu, 2017-11-30 at 23:14 -0800, Cong Wang wrote:
> On Wed, Nov 29, 2017 at 6:25 AM, Paolo Abeni <pabeni@redhat•com> wrote:
> > Currently deleting qdisc with a large number of children and filters
> > can take a lot of time:
> >
> > tc qdisc add dev lo root htb
> > for I in `seq 1 1000`; do
> > tc class add dev lo parent 1: classid 1:$I htb rate 100kbit
> > tc qdisc add dev lo parent 1:$I handle $((I + 1)): htb
> > for J in `seq 1 10`; do
> > tc filter add dev lo parent $((I + 1)): u32 match ip src 1.1.1.$J
> > done
> > done
> > time tc qdisc del dev root
> >
> > real 0m54.764s
> > user 0m0.023s
> > sys 0m0.000s
> >
> > This is due to the multiple rcu_barrier() calls, one for each tcf_block
> > freed, invoked with the rtnl lock held. Most other network related
> > tasks will block in this timespan.
>
> Yeah, Eric pointed out this too and I already had an idea to cure
> this.
>
> As I already mentioned before, my idea is to refcnt the tcf block
> so that we don't need to worry about which is the last. Something
> like the attached patch below, note it is PoC _only_, not even
> compiled yet. And I am not 100% sure it works either, I will look
> deeper tomorrow.
Thank you for the feedback.
I tested your patch and in the above scenario I measure:
real 0m0.017s
user 0m0.000s
sys 0m0.017s
so it apparently works well for this case.
We could still have a storm of rtnl lock/unlock operations while
deleting a large tc tree with lot of filters, and I think we can reduce
them with bulk free, evenutally applying it to filters, too.
That will also reduce the pressure on the rtnl lock when e.g. OVS H/W
offload pushes a lot of rules/sec.
WDYT?
Cheers,
Paolo
next prev parent reply other threads:[~2017-12-01 11:05 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-29 14:25 [RFC PATCH] net_sched: bulk free tcf_block Paolo Abeni
2017-11-29 16:14 ` Alexander Duyck
2017-11-29 18:47 ` Paolo Abeni
2017-12-01 7:14 ` Cong Wang
2017-12-01 11:05 ` Paolo Abeni [this message]
2017-12-01 22:07 ` Cong Wang
2017-12-04 10:12 ` Paolo Abeni
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1512126307.3155.26.camel@redhat.com \
--to=pabeni@redhat$(echo .)com \
--cc=davem@davemloft$(echo .)net \
--cc=jhs@mojatatu$(echo .)com \
--cc=jiri@resnulli$(echo .)us \
--cc=netdev@vger$(echo .)kernel.org \
--cc=xiyou.wangcong@gmail$(echo .)com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox