socket options

[Andrew Bartlett]

On Thu, 2013-02-28 at 16:40 -0500, Scott Lovenberg wrote:
> On 2/28/2013 4:37 PM, Andrew Bartlett wrote:
> > On Thu, 2013-02-28 at 09:37 -0500, Scott Lovenberg wrote:
> >> On Wed, Feb 20, 2013 at 4:47 PM, Scott Lovenberg
> >> <scott.lovenberg at gmail.com>  wrote:
> >>> On Wed, Feb 20, 2013 at 4:27 PM, Andrew Bartlett<abartlet at samba.org>  wrote:
> >>>> On Wed, 2013-02-20 at 16:15 -0500, Scott Lovenberg wrote:
> >>>>> On Sun, Feb 17, 2013 at 4:11 AM, Andrew Bartlett<abartlet at samba.org>  wrote:
> >>>>>> Would you like to write a patch to at least improve the warnings in 'man
> >>>>>> smb.conf'?  Probably not ascii-art, but some clear text explaining why
> >>>>>> this should be the last, not first resort, particularly on Linux.
> >>>>>>
> >>>>>> Thanks,
> >>>>>>
> >>>>>> Andrew Bartlett
> >>>>> How about this wording?  If everyone is ok with it, I'll format it for
> >>>>> a man page and submit it as a patch (since the mailing list hates
> >>>>> non-plain text).
> >>>>>
> >>>>> "
> >>>>> Warning:
> >>>>> "Premature optimization is the root of all evil." -- Donald Knuth
> >>>>>
> >>>>> Changing socket options should be attempted only after consulting the
> >>>>> Samba Performance Tuning chapter of _The Official Samba HOWTO and
> >>>>> Reference Guide_
> >>>>> (http://www.samba.org/samba/docs/man/Samba-HOWTO-Collection/speed.html)
> >>>>> and exhausting all other means of improving performance.
> >>>> The problem with linking to that document is that it is more a source of
> >>>> confusion and outdated information than a solution to it.
> >>>>
> >>>> I'm actually in a mood to totally remove it, or if not to gut it,
> >>>> because I have no indication (in the commit logs) that it has had any
> >>>> significant attention to technical detail in 10 (probably more like 15)
> >>>> years.  (Notice it compares with NT, and mentions NetBEUI as a common
> >>>> network protocol...).
> >>>>
> >>> I just actually read through the entire section.  It is very dated.
> >>> I'm not sure it is relevant any more and I'd understand if you removed
> >>> it entirely.
> >>>
> >>>>> Modern server operating systems are tuned for high network performance
> >>>>> in the majority of situations; when you set socket options you are
> >>>>> overriding those settings.  Linux in particular has an auto-tuning
> >>>>> mechanism for buffer sizes that will be disabled if you specify a
> >>>>> socket buffer size.  This can potentially cripple your TCP/IP stack.
> >>>>>
> >>>>> Getting the socket options correct can make a big difference to your
> >>>>> performance, but getting them wrong can degrade it by just as much.
> >>>>> As with any other low level setting, if you must make changes to it,
> >>>>> make small changes and test the effect before making any large
> >>>>> changes.
> >>>>> "
> >>>>>
> >>>>> Is this wording acceptable?  I could definitely drop the Knuth quote,
> >>>>> but I think it sets the tone perfectly for socket tuning.  Plus, I
> >>>>> like to quote Knuth.
> >>>> Otherwise, I like it.  Perhaps we start with just the last two
> >>>> paragraphs (and the quote, if you can find the right docbook syntax).
> >>>>
> >>> That works for me.  I'll write it up.
> >>>
> >>> --
> >>> Peace and Blessings,
> >>> -Scott.
> >> Sorry for the delay (I got a cold 2 days after getting over a cold.
> >> Never attend a 2 year old's birthday party, there be germs.), I'd like
> >> to make one additional change to the text in regards to Linux.
> >> Apparently, as is currently being discussed on the linux-cifs mailing
> >> list, the TCP_NODELAY socket option is essentially useless on Linux
> >> now that the sockets are "plugged" (ie, like the deadline disk
> >> scheduler does for writes).  The cifs mount utility is doing away with
> >> the option all together, so I think it should be noted in the
> >> documentation that this is another socket option that should not be
> >> used with Linux.
> >>
> >> If there is no objection, I will add that to my doc patch.
> > I would rather not.  Useless options that are ignored are pretty safe,
> > and if they are useful on another OS, then as defaults they should be
> > fine.  We don't need to call it out specifically if they don't do harm.
> > Instead, we want to just warn off making any changes here in general.
> >
> > Andrew Bartlett
> >
> That makes sense.  I'll write it up and submit the patch as worded before.

Thanks.  One more thing: much as I love the quote, please skip it, we
don't do that elsewhere in the manpages.

Andrew Bartlett

-- 
Andrew Bartlett                                http://samba.org/~abartlet/
Authentication Developer, Samba Team           http://samba.org