Messages in this thread | | | Date | Mon, 03 Feb 2003 10:03:48 -0800 | From | Ben Greear <> | Subject | Re: problems achieving decent throughput with latency. |
| |
John Bradford wrote: >>>TCP can only send into a pipe as fast as it can see the >>>ACKs coming back. That is how TCP clocks its sending rate, >>>and latency thus affects that. >> >>Wouldn't you just need larger windows? The problem is latency, not >>bandwidth. > > > Exactly - the original post says that no problems are experienced > using UDP, which backs that up.
I started poking around, and found the tcp_mem, tcp_rmem, and tcp_wmem tunables in /proc/sys/net/ipv4...
If I change the values, I see up to 25Mbps with 25ms of latency. It would go higher, but I have uncovered a performance bug in my code that drops a packet every now and then at those higher rates, so that backs tcp off quickly. I should have that fixed this evening and will continue testing.
Here are the values that I used. The documentation I found is not overly descriptive, so if anyone has any suggestions for improving my tunings, please let me know!
Also, if it's as simple as allocating a few more buffers for tcp, maybe we should consider defaulting to higher in the normal kernel? (I'm not suggesting **my** numbers..)
# See the kernel documentation: Documentation/networking/ip-sysctl.txt my $tcp_rmem_min = 4096; my $tcp_rmem_default = 256000; # TCP specific receive memory pool size. my $tcp_rmem_max = 3000000; # TCP specific receive memory pool size.
my $tcp_wmem_min = 4096; my $tcp_wmem_default = 256000; # TCP specific receive memory pool size. my $tcp_wmem_max = 3000000; # TCP specific receive memory pool size.
my $tcp_mem_lo = 20000000; # Below here there is no memory pressure. my $tcp_mem_pressure = 30000000; # Can use up to 30MB for TCP buffers. my $tcp_mem_high = 30000000; # Can use up to 30MB for TCP buffers.
> > John. > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >
-- Ben Greear <greearb@candelatech.com> <Ben_Greear AT excite.com> President of Candela Technologies Inc http://www.candelatech.com ScryMUD: http://scry.wanfear.com http://scry.wanfear.com/~greear
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |