Netdev Archive on lore.kernel.org
 help / color / Atom feed
From: Thomas Gleixner <tglx@linutronix.de>
To: David Miller <davem@davemloft.net>
Cc: stephen@networkplumber.org, a.darwish@linutronix.de,
	peterz@infradead.org, mingo@redhat.com, will@kernel.org,
	paulmck@kernel.org, bigeasy@linutronix.de, rostedt@goodmis.org,
	linux-kernel@vger.kernel.org, kuba@kernel.org,
	netdev@vger.kernel.org
Subject: Re: [PATCH v1 01/25] net: core: device_rename: Use rwsem instead of a seqcount
Date: Wed, 20 May 2020 21:37:11 +0200
Message-ID: <87wo56v1nc.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20200519.195722.1091264300612213554.davem@davemloft.net>

David Miller <davem@davemloft.net> writes:
> From: Thomas Gleixner <tglx@linutronix.de>
> Date: Wed, 20 May 2020 01:42:30 +0200
>>> Please try, it isn't that hard..
>>>
>>> # time for ((i=0;i<1000;i++)); do ip li add dev dummy$i type dummy; done
>>>
>>> real	0m17.002s
>>> user	0m1.064s
>>> sys	0m0.375s
>> 
>> And that solves the incorrectness of the current code in which way?
>
> You mentioned that there wasn't a test case, he gave you one to try.

If it makes you happy to compare incorrrect code with correct code, here
you go:

5 runs of 1000 device add, 1000 device rename and 1000 device del

CONFIG_PREEMPT_NONE=y

         Base      rwsem
 add     0:05.01   0:05.28
	 0:05.93   0:06.11
	 0:06.52   0:06.26
	 0:06.06   0:05.74
	 0:05.71   0:06.07

 rename  0:32.57   0:33.04
	 0:32.91   0:32.45
	 0:32.72   0:32.53
	 0:39.65   0:34.18
	 0:34.52   0:32.50

 delete  3:48.65   3:48.91
	 3:49.66   3:49.13
	 3:45.29   3:48.26
	 3:47.56   3:46.60
	 3:50.01   3:48.06

 -------------------------

CONFIG_PREEMPT_VOLUNTARY=y

         Base      rwsem
 add     0:06.80   0:06.42
	 0:04.77   0:05.03
	 0:05.74   0:04.62
	 0:05.87   0:04.34
	 0:04.20   0:04.12

 rename  0:33.33   0:42.02
	 0:42.36   0:32.55
	 0:39.58   0:31.60
	 0:33.69   0:35.08
	 0:34.24   0:33.97

 delete  3:47.82   3:44.00
	 3:47.42   3:51.00
	 3:48.52   3:48.88
	 3:48.50   3:48.09
	 3:50.03   3:46.56

 -------------------------

CONFIG_PREEMPT=y

         Base      rwsem

 add     0:07.89   0:07.72
	 0:07.25   0:06.72
	 0:07.42   0:06.51
	 0:06.92   0:06.38
	 0:06.20   0:06.72

 rename  0:41.77   0:32.39
	 0:44.29   0:33.29
	 0:36.19   0:34.86
	 0:33.19   0:35.06
	 0:37.00   0:34.78

 delete  2:36.96   2:39.97
	 2:37.80   2:42.19
	 2:44.66   2:48.40
	 2:39.75   2:41.02
	 2:40.77   2:38.36

The runtime variation is rather large and when running the same in a VM
I got complete random numbers for both base and rwsem. The most amazing
was delete where the time varies from 30s to 6m20s.

Btw, Sebastian noticed that rename spams dmesg:

  netdev_info(dev, "renamed from %s\n", oldname);

which eats about 50% of the Rename run time.

         Base      netdev_info() removed

Rename   0:34.84   0:17.48

That number at least makes tons of sense

Thanks,

        tglx

  parent reply index

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-19 21:45 [PATCH v1 00/25] seqlock: Extend seqcount API with associated locks Ahmed S. Darwish
2020-05-19 21:45 ` [PATCH v1 01/25] net: core: device_rename: Use rwsem instead of a seqcount Ahmed S. Darwish
2020-05-19 22:01   ` Stephen Hemminger
2020-05-19 22:23     ` Thomas Gleixner
2020-05-19 23:11       ` Stephen Hemminger
2020-05-19 23:42         ` Thomas Gleixner
2020-05-20  0:06           ` Stephen Hemminger
2020-05-20  1:55             ` Thomas Gleixner
2020-05-20  2:57           ` David Miller
2020-05-20  3:18             ` Eric Dumazet
2020-05-20  4:36               ` Stephen Hemminger
2020-05-20 19:37             ` Thomas Gleixner [this message]
2020-05-20 21:36               ` Stephen Hemminger
2020-05-20  2:01   ` Eric Dumazet
2020-05-20  6:42     ` Ahmed S. Darwish
2020-05-20 12:51       ` Eric Dumazet
2020-06-03 14:33         ` Ahmed S. Darwish
2020-05-20 14:37   ` Dan Carpenter
2020-05-25 16:22     ` Ahmed S. Darwish
2020-05-19 21:45 ` [PATCH v1 03/25] net: phy: fixed_phy: Remove unused seqcount Ahmed S. Darwish
2020-05-19 21:45 ` [PATCH v1 05/25] u64_stats: Document writer non-preemptibility requirement Ahmed S. Darwish
2020-05-19 21:45 ` [PATCH v1 15/25] netfilter: conntrack: Use sequence counter with associated spinlock Ahmed S. Darwish
2020-05-19 21:45 ` [PATCH v1 16/25] netfilter: nft_set_rbtree: Use sequence counter with associated rwlock Ahmed S. Darwish
2020-05-19 21:45 ` [PATCH v1 17/25] xfrm: policy: Use sequence counters with associated lock Ahmed S. Darwish
2020-06-08  0:57 ` [PATCH v2 00/18] seqlock: Extend seqcount API with associated locks Ahmed S. Darwish
2020-06-08  0:57   ` [PATCH v2 08/18] netfilter: conntrack: Use sequence counter with associated spinlock Ahmed S. Darwish
2020-06-08  0:57   ` [PATCH v2 09/18] netfilter: nft_set_rbtree: Use sequence counter with associated rwlock Ahmed S. Darwish
2020-06-08  0:57   ` [PATCH v2 10/18] xfrm: policy: Use sequence counters with associated lock Ahmed S. Darwish
2020-06-30  5:44 ` [PATCH v3 00/20] seqlock: Extend seqcount API with associated locks Ahmed S. Darwish
2020-06-30  5:44   ` [PATCH v3 10/20] netfilter: conntrack: Use sequence counter with associated spinlock Ahmed S. Darwish
2020-06-30  5:44   ` [PATCH v3 11/20] netfilter: nft_set_rbtree: Use sequence counter with associated rwlock Ahmed S. Darwish
2020-06-30  5:44   ` [PATCH v3 12/20] xfrm: policy: Use sequence counters with associated lock Ahmed S. Darwish
2020-07-20 15:55 ` [PATCH v4 00/24] seqlock: Extend seqcount API with associated locks Ahmed S. Darwish
2020-07-20 15:55   ` [PATCH v4 14/24] netfilter: conntrack: Use sequence counter with associated spinlock Ahmed S. Darwish
2020-07-20 15:55   ` [PATCH v4 15/24] netfilter: nft_set_rbtree: Use sequence counter with associated rwlock Ahmed S. Darwish
2020-07-20 15:55   ` [PATCH v4 16/24] xfrm: policy: Use sequence counters with associated lock Ahmed S. Darwish
2020-07-20 16:49   ` [PATCH v4 00/24] seqlock: Extend seqcount API with associated locks Eric Biggers
2020-07-20 17:33     ` Ahmed S. Darwish

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=87wo56v1nc.fsf@nanos.tec.linutronix.de \
    --to=tglx@linutronix.de \
    --cc=a.darwish@linutronix.de \
    --cc=bigeasy@linutronix.de \
    --cc=davem@davemloft.net \
    --cc=kuba@kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=netdev@vger.kernel.org \
    --cc=paulmck@kernel.org \
    --cc=peterz@infradead.org \
    --cc=rostedt@goodmis.org \
    --cc=stephen@networkplumber.org \
    --cc=will@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Netdev Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/netdev/0 netdev/git/0.git
	git clone --mirror https://lore.kernel.org/netdev/1 netdev/git/1.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 netdev netdev/ https://lore.kernel.org/netdev \
		netdev@vger.kernel.org
	public-inbox-index netdev

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.netdev


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git