Re: [GIT PULL] kdbus for 4.1-rc1

Greg Kroah-Hartman
2015-04-24T08:35:08Z

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