From: Eric Dumazet <eric.dumazet@gmail.com>
To: Nick Piggin <npiggin@suse.de>
Cc: David Miller <davem@davemloft.net>,
netdev@vger.kernel.org, bhutchings@solarflare.com
Subject: Re: [PATCH net-next-2.6] net: Introduce u64_stats_sync infrastructure
Date: Tue, 15 Jun 2010 14:12:52 +0200 [thread overview]
Message-ID: <1276603972.2541.99.camel@edumazet-laptop> (raw)
In-Reply-To: <20100615110413.GJ6138@laptop>
Le mardi 15 juin 2010 à 21:04 +1000, Nick Piggin a écrit :
> So if you have a regular seqlock, the sequence:
>
> write_seqcount_begin
> stat1++
> stat2--
> write_seqcount_end
>
> do read_seqcount_begin
> sum = stat1+stat2;
> while (read_seqcount_retry)
> BUG_ON(sum != 0);
>
> This code is OK. But if it is using your stat sync, then it is buggy.
> This is obvious to you of course, but someone who doesn't consider
> the implementation might get caught out.
>
> I guess all my other points are properties of seqcount code itself,
> but they are not documented really well with the seqlock API
> unfortunately.
>
Yep, not counting fact that stat_sync is a noop on 64 bits anyway, so
external synchronization is pretty much needed (and probably already
present on all path were I need this stuff. If not, it must be fixed)
next prev parent reply other threads:[~2010-06-15 12:18 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-06-14 15:59 [PATCH net-next-2.6] loopback: Implement 64bit stats on 32bit arches Eric Dumazet
2010-06-15 6:14 ` David Miller
2010-06-15 6:49 ` Nick Piggin
2010-06-15 7:23 ` Eric Dumazet
2010-06-15 10:14 ` [PATCH net-next-2.6] net: Introduce u64_stats_sync infrastructure Eric Dumazet
2010-06-15 10:25 ` Nick Piggin
2010-06-15 10:43 ` Eric Dumazet
2010-06-15 11:04 ` Nick Piggin
2010-06-15 12:12 ` Eric Dumazet [this message]
2010-06-15 13:29 ` [PATCH net-next-2.6 v2] " Eric Dumazet
2010-06-22 17:24 ` David Miller
2010-06-22 17:31 ` Eric Dumazet
2010-06-15 10:39 ` [PATCH net-next-2.6] bridge: 64bit rx/tx counters Eric Dumazet
2010-06-22 17:25 ` David Miller
2010-08-10 4:47 ` Andrew Morton
2010-08-12 12:16 ` Eric Dumazet
2010-08-12 15:07 ` Andrew Morton
2010-08-12 21:47 ` Eric Dumazet
2010-08-12 22:11 ` Andrew Morton
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=1276603972.2541.99.camel@edumazet-laptop \
--to=eric.dumazet@gmail.com \
--cc=bhutchings@solarflare.com \
--cc=davem@davemloft.net \
--cc=netdev@vger.kernel.org \
--cc=npiggin@suse.de \
/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
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