Re: BUG: Slowdown on 3000 socket-machines tracked down

Christian Schmid
2005-03-09T23:59:02Z

> Yes, 2.6.11. I have tuned max_backlog and some other TCP and networking
> related settings to give more buffers etc to networking tasks. I have not
> tried any significant disk-IO while doing these tests.
>
> I finally got my systems set up so I can run my WAN emulator at full 1Gbps:
>
> I am getting right at 986Mbps throughput with 30ms round-trip latency
> (15ms in both directions).
>
> So, latency does not seem to be the problem either.
>
> I think the problem can be narrowed down to:
>
> 1) Non-optimal kernel network tunings on your server.

I used all the default-settings on 2.6.11

> 2) Disk-IO (my disk is small and slow compared to a 'real' server, not
> sure I can
> really test this side of things, and I have not tried as of yet.)

This doesnt explain the speed-up when I change lower_zone_protection from 0 to 1024. It also doesnt
explain the slowdown on 2.6.11 compared to 2.6.10

> 3) Your clients have much more latency and/or don't have enough bandwidth
> to fully load your server. Since you didn't answer before: I
> assume you
> do not have a reliable test bed and are just hoping that enough
> clients connect
> to do your benchmarking.

Yes I just wait until they connect. On the graph it only takes about 2 minutes until 3000 sockets
are created again.

> 4) There is something strange with sendfile and/or your application's
> coding.

I am not doing more than calling sendfile. There is nothing one can do wrong.

> My suggestion would be to eliminate these variables by coming up with a
> repeatable
> test bed, alternative traffic generators, WAN/Network emulators for
> latency, etc.

The problem still is that 1) it speeds up immediately when lower_zone_protection is raised to 1024.
This proves it is NOT a disk-bottleneck. And second: it got much worse with 2.6.11 and
lower_zone_protection disappeared on 2.6.11

Chris