nginx not responding to some SYN packets

[Radek Burkat]

Thanks Igor, for eliminating one variable for me. I noticed that when I use
a single worker and set the affinity to the same core as the ethernet
interface interrupt I decrease the frequency of the issue but do not
eliminate it.  Not sure
Are there any kernel/network debugging tools which reach a little deeper
than tcpdump?

Radek

On Tue, Feb 3, 2009 at 10:11 PM, Igor Sysoev <is at rambler-co.ru> wrote:

> On Tue, Feb 03, 2009 at 10:07:27PM -0800, Radek Burkat wrote:
>
> > Have a machine running the latest devel version nginx-0.7.33 (tried
> 0.6.35
> > with same results) for serving small (less than 10K images) and am seeing
> on
> > tcpdump that some SYN packets are not responded to right away.The browser
> > does retransmit these image requests every second and on the 2nd or 3rd
> > resent SYN, I finally start seeing and ACK, and the images load.
> > It is very indeterministic as to when it happens and can only reproduce
> it
> > some of the time.  When it does occur the outcome is a page with some
> images
> > loaded and others (whose SYN packets are not ACKs) are not loaded.....a
> few
> > seconds later they load.
> > Typically the system has ~2000 active connections, most in keep alive.
>  The
> > load is around 100-200 req/sec.
> >
> > I have tries all sorts of settings and configurations suggested in the
> > maillist but I still dont have the solution for this issue.  from 1 to 4
> > workers, changing the connection counts, different even handlers, kernel
> > buffers, etc.
> > It just seems so anecdotal to just change a bunch of settings without
> being
> > able to what is happening internally.
> > I'd like to be able to debug a little deeper to find out what is
> happening
> > to these packets.
> >
> > How would I go about debugging what is the cause of it.  Is it the
> interface
> > driver, kernel, or nginx?  What kind of tools and debugging options can I
> > try next?
>
> nginx has not any relation to TCP handshake (SYN, SYN/ACK, ACK),
> this is kernel or driver issue.
>
> > Thanks, Radek
> >
> >
> > System Details
> > model name : Intel(R) Xeon(R) CPU X3210 @ 2.13GHz
> > Linux n06 2.6.18-92.1.22.el5 #1 SMP Tue Dec 16 12:03:43 EST 2008 i686
> i686
> > i386 GNU/Linux
> > eth0
> > Advertised auto-negotiation: Yes
> > Speed: 1000Mb/s
> > Duplex: Full
> > Port: Twisted Pair
> > PHYAD: 1
> > Transceiver: internal
> > Auto-negotiation: on
> > Supports Wake-on: g
> > Wake-on: d
> > Current message level: 0x000000ff (255)
> > Link detected: yes
> > driver: tg3
> > version: 3.86
> > firmware-version: 5721-v3.61, ASFIPMI v6.21
> > bus-info: 0000:05:00.0
> >
> > avg-cpu: %user %nice %system %iowait %steal %idle
> > 0.10 0.00 0.20 2.43 0.00 97.27
> > Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm
> > %util
> > sda 0.00 0.00 27.40 0.00 443.20 0.00 16.18 0.10 3.50 3.32 9.10
> > no overruns or errors on interface.
>
> --
> Igor Sysoev
> http://sysoev.ru/en/
>
>
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