Date: Fri, 24 Apr 2015 08:45:15 +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
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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.

greg k-h
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