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From Colm MacCarthaigh <c...@stdlib.net>
Subject Re: do we still want sendfile enabled with our default conf files?
Date Thu, 17 Mar 2005 17:37:38 GMT
On Thu, Mar 17, 2005 at 07:27:54AM -0800, Justin Erenkrantz wrote:
> These seem like broken OSes and not a suitable justification to disable
> sendfile.  We should fix the code - perhaps by teaching APR not to enable the
> sendfile-variants on these buggy platforms - not disable it entirely.  For
> those platforms that don't have bugs, 

It's not simply a question of OS bugs. The Linux/IPv6 problem is
actually a symptom of TCP checksum-offloading bugs in most network
interface cards. In an effort to speed up sendfile() even more, Linux
lets the NiC handle the TCP checksumming, and most cards niaively assume
an IPv4 header and that the payload starts 20-bytes in (which it doesn't
for IPv6). So it's not entirely fair to blame the OS developers, or to
expect maintaining an "on" default for EnableSendfile to exert much
useful pressure on people to fix the bugs :(

> disabling sendfile would be a ridiculous performance hit.  -1.  -- justin

Is there any quantification of this? I'm not entirely convinced of the
performance hit, mostly - network writes tend to be network-IO bound no
matter what, and I've yet to see much of a CPU/Memory hit using my own
benchmarks, with MMap. But I've only run them on Linux and the ammount
of Ram I have may be distorting the truth of it.

-- 
Colm MacCárthaigh                        Public Key: colm+pgp@stdlib.net

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