On 01/24/2013 11:21 AM, Leandro Lucarella wrote: > On Thu, Jan 24, 2013 at 10:44:32AM -0800, Rick Jones wrote: >> On 01/24/2013 04:22 AM, Leandro Lucarella wrote: >>> On Wed, Jan 23, 2013 at 11:28:08AM -0800, Rick Jones wrote: >>>>> Then if syncookies are enabled, the time spent in connect() shouldn't be >>>>> bigger than 3 seconds even if SYNs are being "dropped" by listen, right? >>>> >>>> Do you mean if "ESTABLISHED" connections are dropped because the >>>> listen queue is full? I don't think I would put that as "SYNs being >>>> dropped by listen" - too easy to confuse that with an actual >>>> dropping of a SYN segment. >>> >>> I was just kind of quoting the name given by netstat: "SYNs to LISTEN >>> sockets dropped" (for kernel 3.0, I noticed newer kernels don't have >>> this stat anymore, or the name was changed). I still don't know if we >>> are talking about the same thing. >> [snip] >> I will sometimes be tripped-up by netstat's not showing a statistic >> with a zero value...
Leandro, you should be able to do an nstat -z, it will print all counters even if zero. You should see something like so: ipv4]> nstat -z #kernel IpInReceives 2135 0.0 IpInHdrErrors 0 0.0 IpInAddrErrors 202 0.0 ... You might want to take a look at those (your pkts may not even be making it to tcp) and these in particular: TcpExtSyncookiesSent 0 0.0 TcpExtSyncookiesRecv 0 0.0 TcpExtSyncookiesFailed 0 0.0 TcpExtListenOverflows 0 0.0 TcpExtListenDrops 0 0.0 TcpExtTCPBacklogDrop 0 0.0 TcpExtTCPMinTTLDrop 0 0.0 TcpExtTCPDeferAcceptDrop 0 0.0 If you don't have nstat on that version for some reason, download the latest iproute pkg. Looking at the counter names is a lot more helpful and precise than the netstat converstion to human consumption. > Yes, I already did captures and we are definitely loosing packets > (including SYNs), but it looks like the amount of SYNs I'm loosing is > lower than the amount of long connect() times I observe. This is not > confirmed yet, I'm still investigating. Where did you narrow down the drop to? There are quite a few places in the networking stack we silently drop packets (such as the one pointed out earlier in this thread), although they should almost all be extremely low probability/NEVER type events. Do you want a patch to gap the most likely scenario? (I'll post that to netdev separately). thanks, Nivedita -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
