Date: Fri, 24 Apr 2015 10:35:01 +0200
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Borislav Petkov <bp@alien8.de>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Arnd Bergmann <arnd@arndb.de>, gnomes@lxorguk.ukuu.org.uk, teg@jklm.no,
        jkosina@suse.cz, luto@amacapital.net, linux-kernel@vger.kernel.org,
        daniel@zonque.org, dh.herrmann@gmail.com, tixxdz@opendz.org
Subject: Re: [GIT PULL] kdbus for 4.1-rc1
Message-ID: <20150424083501.GB7782@kroah.com>
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 <20150422085827.GA6962@pd.tnic>
 <20150423191433.GB13607@kroah.com>
 <20150423205640.GR28327@pd.tnic>
 <20150424063603.GA4790@kroah.com>
 <20150424064515.GA5103@kroah.com>
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On Fri, Apr 24, 2015 at 08:45:15AM +0200, Greg Kroah-Hartman wrote:
> On Fri, Apr 24, 2015 at 08:36:03AM +0200, Greg Kroah-Hartman wrote:
> > On Thu, Apr 23, 2015 at 10:56:40PM +0200, Borislav Petkov wrote:
> > > > Hm, this seems to be to be O(1), pretty constant, we do the same amount
> > > > of work all the time.
> > > 
> > > The same *pile* of unnecessary and needless work. You go and collect
> > > *all* that data on *every* packet send?!
> > 
> > No, not at all, the metadata is cached, we only collect that for the
> > first message sent, if we didn't know it already, or we do it on the
> > "open" of the connection, depending on what we are gathering metadata
> > for.
> > 
> > The mc->collected test right before collecting the specific metadata is
> > that "cached or not" test.
> 
> Oh wait, no, there are some send-time metadata that is collected for
> every message, see Linus's email for more details about that.  Maybe
> this can be changed to cache things even more than we currently do.
> 
> it's early, shouldn't write emails before coffee...
> 
> David had some flamegraphs floating around that showed where all the
> time on transmit / receive was being spent, and I don't think that the
> metadata area was all that relevant, but I can't find them anymore to
> say for sure.  There are other areas that can be sped up on the send
> path, but perf data is the best way to verify this.

Here's the graphs that he posted during the last code review cycle that
are relevant here:
	http://lkml.iu.edu/hypermail/linux/kernel/1503.2/02624.html

greg k-h
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