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Date: Tue, 09 Nov 2010 15:38:36 +0100
From: Jesper Dangaard Brouer <jdb@...x.dk>
To: Eric Dumazet <eric.dumazet@...il.com>
Cc: netdev <netdev@...r.kernel.org>
Subject: Re: Loopback performance from kernel 2.6.12 to 2.6.37
On Tue, 2010-11-09 at 15:16 +0100, Jesper Dangaard Brouer wrote:
> On Tue, 2010-11-09 at 14:59 +0100, Jesper Dangaard Brouer wrote:
> > On Mon, 2010-11-08 at 16:06 +0100, Eric Dumazet wrote:
> > ...
> > > > > > > I noticed that the loopback performance has gotten quite bad:
> > > > > > >
> > > > > > > http://www.phoronix.com/scan.php?page=article&item=linux_2612_2637&num=6
>
> > > Their network test is basically :
> > >
> > > netcat -l 9999 >/dev/null &
> > > time dd if=/dev/zero bs=1M count=10000 | netcat 127.0.0.1 9999
> >
> > Should it not be:
> > netcat -l -p 9999 >/dev/null &
> >
> > When I run the commands "dd | netcat", netcat never finish/exits, I have
> > to press Ctrl-C to stop it. What am I doing wrong? Any tricks?
>
> To fix this I added "-q 0" to netcat. Thus my working commands are:
>
> netcat -l -p 9999 >/dev/null &
> time dd if=/dev/zero bs=1M count=10000 | netcat -q0 127.0.0.1 9999
>
> Running this on my "big" 10G testlab system, Dual Xeon 5550 2.67GHz,
> kernel version 2.6.32-5-amd64 (which I usually don't use)
> The results are 7.487 sec
Using kernel 2.6.35.8-comx01+ (which is 35-stable with some minor
patches of my own) on the same type of hardware (our preprod server).
The result is 12 sec.
time dd if=/dev/zero bs=1M count=10000 | netcat -q0 127.0.0.1 9999
10000+0 records in
10000+0 records out
10485760000 bytes (10 GB) copied, 12,0805 s, 868 MB/s
real 0m12.082s
user 0m0.311s
sys 0m15.896s
BUT perf top reveals that its probably related to the function
'find_busiest_group' ... any kernel config hints how I get rid of that?
samples pcnt function DSO
_______ _____ ___________________________ ______________
4152.00 12.8% copy_user_generic_string [kernel]
1802.00 5.6% find_busiest_group [kernel]
852.00 2.6% __clear_user [kernel]
836.00 2.6% _raw_spin_lock_bh [kernel]
819.00 2.5% ipt_do_table [ip_tables]
628.00 1.9% rebalance_domains [kernel]
564.00 1.7% _raw_spin_lock [kernel]
562.00 1.7% _raw_spin_lock_irqsave [kernel]
522.00 1.6% schedule [kernel]
441.00 1.4% find_next_bit [kernel]
413.00 1.3% _raw_spin_unlock_irqrestore [kernel]
394.00 1.2% tcp_sendmsg [kernel]
391.00 1.2% tcp_packet [nf_conntrack]
368.00 1.1% do_select [kernel]
> Using vmstat I see approx 400000 context switches per sec.
>
Previous:
> Perf top says:
> samples pcnt function DSO
> _______ _____ _________________________ ___________
>
> 6442.00 16.3% copy_user_generic_string [kernel]
> 2226.00 5.6% __clear_user [kernel]
> 912.00 2.3% _spin_lock_irqsave [kernel]
> 773.00 2.0% _spin_lock_bh [kernel]
> 736.00 1.9% schedule [kernel]
> 582.00 1.5% ipt_do_table [ip_tables]
> 569.00 1.4% _spin_lock [kernel]
> 505.00 1.3% get_page_from_freelist [kernel]
> 451.00 1.1% _spin_unlock_irqrestore [kernel]
> 434.00 1.1% do_select [kernel]
> 354.00 0.9% tcp_sendmsg [kernel]
> 348.00 0.9% tick_nohz_stop_sched_tick [kernel]
> 347.00 0.9% tcp_transmit_skb [kernel]
> 345.00 0.9% zero_fd_set [kernel]
--
Jesper Dangaard Brouer
ComX Networks A/S
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