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From: Wu Fengguang on 2 Mar 2010 20:50
On Wed, Mar 03, 2010 at 04:14:33AM +0800, Bret Towe wrote:

> how do you determine which bdi to use? I skimmed thru
> the filesystem in /sys and didn't see anything that says which is what

MOUNTPOINT=" /mnt/ext4_test "
# grep "$MOUNTPOINT" /proc/$$/mountinfo|awk '{print $3}'
0:24

Thanks,
Fengguang
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From: Wu Fengguang on 2 Mar 2010 22:30
On Wed, Mar 03, 2010 at 02:42:19AM +0800, Trond Myklebust wrote:
> On Tue, 2010-03-02 at 12:33 -0500, John Stoffel wrote:
> > >>>>> "Trond" == Trond Myklebust <Trond.Myklebust(a)netapp.com> writes:
> >
> > Trond> On Tue, 2010-03-02 at 11:10 +0800, Wu Fengguang wrote:
> > >> Dave,
> > >>
> > >> Here is one more test on a big ext4 disk file:
> > >>
> > >> 16k 39.7 MB/s
> > >> 32k 54.3 MB/s
> > >> 64k 63.6 MB/s
> > >> 128k 72.6 MB/s
> > >> 256k 71.7 MB/s
> > >> rsize ==> 512k 71.7 MB/s
> > >> 1024k 72.2 MB/s
> > >> 2048k 71.0 MB/s
> > >> 4096k 73.0 MB/s
> > >> 8192k 74.3 MB/s
> > >> 16384k 74.5 MB/s
> > >>
> > >> It shows that >=128k client side readahead is enough for single disk
> > >> case :) As for RAID configurations, I guess big server side readahead
> > >> should be enough.
> >
> > Trond> There are lots of people who would like to use NFS on their
> > Trond> company WAN, where you typically have high bandwidths (up to
> > Trond> 10GigE), but often a high latency too (due to geographical
> > Trond> dispersion). My ping latency from here to a typical server in
> > Trond> NetApp's Bangalore office is ~ 312ms. I read your test results
> > Trond> with 10ms delays, but have you tested with higher than that?
> >
> > If you have that high a latency, the low level TCP protocol is going
> > to kill your performance before you get to the NFS level. You really
> > need to open up the TCP window size at that point. And it only gets
> > worse as the bandwidth goes up too.
>
> Yes. You need to open the TCP window in addition to reading ahead
> aggressively.

I only get ~10MB/s throughput with following settings.

# huge NFS ra size
echo 89512 > /sys/devices/virtual/bdi/0:15/read_ahead_kb

# on both sides
/sbin/tc qdisc add dev eth0 root netem delay 200ms

net.core.rmem_max = 873800000
net.core.wmem_max = 655360000
net.ipv4.tcp_rmem = 8192 87380000 873800000
net.ipv4.tcp_wmem = 4096 65536000 655360000

Did I miss something?

Thanks,
Fengguang
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