[squid-users] Howto: Squid3 on Debian Sarge with Linux 2.6 + NPTL + epoll

Hello,

I tried the latest Squid3 today on Debian Sarge (testing) with Linux
2.6.3, NPTL and epoll and I was quite satisfied with it after a small
test run. For everyone else interested trying it, I wrote a small
howto-stylish description how to do it quite easily.

If you don't know what NPTL and epoll are and why Linux 2.6 is (afaik)
better for Squid3 than 2.4, here are short explanations:

NPTL (The Native POSIX Thread Library for Linux) is a new thread library
for Linux which is going to replace the old LinuxThreads-library
distributed with glibc by many Linux-distributions. Old implementation
is based on the principles outlined by the kernel developers at the time
the code was written, 1996. Since that, many new kernel extensions have
been introduced to kernel which makes it possible to create a new thread
library far better than the old LinuxThreads in scalability and
performance. For example Redhat has already included NPTL in their Red
Hat Linux 9 and Enterprise-editions and others will probably follow.
Squid uses threads for example with aufs. For more information about
NPTL and it's design, read http://people.redhat.com/drepper/nptl-design.pdf

Epoll is a replacement for poll which is used to delivery network events
from kernel mode to user mode (here, Squid3). Because Squid3 heavily
depends on network I/O, efficient delivery of events is vital. For more
information about epoll and it's efficiency (for example compared to
traditional poll), check
http://www.xmailserver.org/linux-patches/nio-improve.html

Linux 2.6 kernel introduced (for example) a new mmap syscall which is
O(1) compared to the old implementation of O(n). For cache/proxy servers
it is important to map files into memory instead of having a buffer and
reading the file contents into the buffer. Mapping the file into memory
directly leaves more free memory for operating system to do I/O
buffering. This is what the mmap syscall is used for. What does O(1) and
O(n) mean, then? O(1) (ordo one) means that the operation (execution of
mmap syscall) is always executed in a fixed time -- number of mapped
pages doesn't matter. O(n) (ordo n) means that the number of pages has
an effect on the execution time (here, linear) -- the more pages, the
longer it takes. There's a page on the WWW that has some benchmarks
about BSD and Linux but also Linux 2.4 and 2.6. This page is located at
http://bulk.fefe.de/scalability

After this short (hopefully) explanatory part, I assume that you have at
least base install of Sarge running and have some knowledge on using apt
and compiling stuff (like Linux kernel). Also remember that if you use
epoll, you can't use delay pools or deferred reads (there is a notice
about this in comm_epoll.cc).

1. Install all Debian packages needed to compile 2.6 kernel and Squid3
(you will need at least libc6-dev, bin86, binutils, make, gcc and g++).

2. Install Debian package "module-init-tools" which is needed for
loading modules of 2.6 kernel. Sarge's scripts are smart enough to check
which kernel version (2.4 or 2.6) you're running and uses the correct
version of these tools, so you don't have to worry about this if you
want to revert back to 2.4 kernel later.

3. Get the source code for 2.6 (for example from www.kernel.org's
mirror), compile and reboot with it. This is needed for NPTL and epoll
to work (it will work with 2.4 too, but it will need some serious patching).

4. Install Debian package "libc6-i686". This is an i686 optimized
version of libc6 (so you will need a i686 class CPU, ie. "uname -m"
should print "i686"). What's more important, it includes NPTL instead of
LinuxThreads.

5. Extract Squid3 sources and execute configure. Remember to include
"--enable-epoll --with-pthreads" on your configure line among other
parameters you want.

6. Remove all occurences of "-lepoll" from Squid3's src/Makefile. This
has to be done because Sarge's libc6-dev already contains epoll support
and separate epoll library is not needed (Squid3 will probably figure
this out itself in future). I counted four occurences. Then compile
Squid with "make" and install it with "make install".

7. You should now have Squid3 compiled with NPTL and epoll. Go have fun
with it.

And always the so needed disclaimer: I do not take any responsibility if
something goes wrong and so on. Squid3 is not yet production ready so do
not expect too much.

Comments and corrections on the list, please. :-)

Regards,

-- 
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