From: Joe Perches <joe@perches•com>
To: "Jason A. Donenfeld" <Jason@zx2c4•com>
Cc: Andrew Morton <akpm@linux-foundation•org>,
"David S. Miller" <davem@davemloft•net>,
netdev@vger•kernel.org, linux-kernel@vger•kernel.org
Subject: Re: [PATCH] net_dbg_ratelimited: turn into no-op when !DEBUG
Date: Mon, 03 Aug 2015 20:57:57 -0700 [thread overview]
Message-ID: <1438660677.10829.1.camel@perches.com> (raw)
In-Reply-To: <1438658773-3220-1-git-send-email-Jason@zx2c4.com>
On Tue, 2015-08-04 at 05:26 +0200, Jason A. Donenfeld wrote:
> The pr_debug family of functions turns into a no-op when -DDEBUG is not
> specified, opting instead to call "no_printk", which gets compiled to a
> no-op (but retains gcc's nice warnings about printf-style arguments).
>
> The problem with net_dbg_ratelimited is that it is defined to be a
> variant of net_ratelimited_function, which expands to essentially:
>
> if (net_ratelimit())
> pr_debug(fmt, ...);
>
> When DEBUG is not defined, then this becomes,
>
> if (net_ratelimit())
> ;
>
> This seems benign, except it isn't. Firstly, there's the obvious
> overhead of calling net_ratelimit needlessly, which does quite some book
> keeping for the rate limiting. Given that the pr_debug and
> net_dbg_ratelimited family of functions are sprinkled liberally through
> performance critical code, with developers assuming they'll be compiled
> out to a no-op most of the time, we certainly do not want this needless
> book keeping. Secondly, and most visibly, even though no debug message
> is printed when DEBUG is not defined, if there is a flood of
> invocations, dmesg winds up peppered with messages such as
> "net_ratelimit: 320 callbacks suppressed". This is because our
> aforementioned net_ratelimit() function actually prints this text in
> some circumstances. It's especially odd to see this when there isn't any
> other accompanying debug message.
>
> So, in sum, it doesn't make sense to have this function's current
> behavior, and instead it should match what every other debug family of
> functions in the kernel does with !DEBUG -- nothing.
>
> This patch replaces calls to net_dbg_ratelimited when !DEBUG with
> no_printk, keeping with the idiom of all the other debug print helpers.
Makes sense, thanks Jason.
next prev parent reply other threads:[~2015-08-04 3:57 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-04 3:26 [PATCH] net_dbg_ratelimited: turn into no-op when !DEBUG Jason A. Donenfeld
2015-08-04 3:57 ` Joe Perches [this message]
2015-08-04 4:02 ` Joe Perches
2015-08-04 4:59 ` David Miller
2015-08-04 15:07 ` Jason A. Donenfeld
2015-08-04 15:08 ` Jason A. Donenfeld
2015-08-04 15:51 ` Joe Perches
2015-08-04 16:26 ` [PATCH v3] " Jason A. Donenfeld
2015-08-07 6:51 ` David Miller
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=1438660677.10829.1.camel@perches.com \
--to=joe@perches$(echo .)com \
--cc=Jason@zx2c4$(echo .)com \
--cc=akpm@linux-foundation$(echo .)org \
--cc=davem@davemloft$(echo .)net \
--cc=linux-kernel@vger$(echo .)kernel.org \
--cc=netdev@vger$(echo .)kernel.org \
/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