From: Alkis Georgopoulos <alkisg@gmail.com>
To: "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>
Subject: Re: rsize,wsize=1M causes severe lags in 10/100 Mbps
Date: Sat, 21 Sep 2019 10:59:55 +0300 [thread overview]
Message-ID: <675724ca-bdb4-324b-b3ec-2fba608b8358@gmail.com> (raw)
In-Reply-To: <ddf47f3c-d27e-972b-fd38-1fdfeaa105a3@gmail.com>
On 9/21/19 10:52 AM, Alkis Georgopoulos wrote:
> I think it's caused by the kernel readahead, not glibc readahead.
> TL;DR: This solves the problem:
> echo 4 > /sys/devices/virtual/bdi/0:58/read_ahead_kb
>
> Question: how to configure NFS/kernel to automatically set that?
>
> Long version:
> Doing step (4) below results in tremendous speedup:
>
> 1) mount -t nfs -o tcp,timeo=600,rsize=1048576,wsize=1048576
> 10.161.254.11:/srv/ltsp /mnt
>
> 2) cat /proc/fs/nfsfs/volumes
> We see the DEV number from there, e.g. 0:58
>
> 3) cat /sys/devices/virtual/bdi/0:58/read_ahead_kb
> 15360
> I assume that this means the kernel will try to read ahead up to 15 MB
> for each accessed file. *THIS IS THE PROBLEM*. For non-NFS devices, this
> value is 128 (KB).
>
> 4) echo 4 > /sys/devices/virtual/bdi/0:58/read_ahead_kb
>
> 5) Test. Traffic now should be a *lot* less, and speed a *lot* more.
> E.g. my NFS booting tests:
> - read_ahead_kb=15360 (the default) => 1160 MB traffic to boot
> - read_ahead_kb=128 => 324MB traffic
> - read_ahead_kb=4 => 223MB traffic
>
> So the question that remains, is how to properly configure either NFS or
> the kernel, to use small readahead values for NFS.
>
> I'm currently doing it with this workaround:
> for f in $(awk '/^v[0-9]/ { print $4 }' < /proc/fs/nfsfs/volumes); do
> echo 4 > /sys/devices/virtual/bdi/$f/read_ahead_kb; done
>
> Thanks,
> Alkis
Quoting https://lkml.org/lkml/2010/2/26/48
> nfs: use 2*rsize readahead size
> With default rsize=512k and NFS_MAX_READAHEAD=15, the current NFS
> readahead size 512k*15=7680k is too large than necessary for typical
> clients.
I.e. the problem probably is that when NFS_MAX_READAHEAD=15 was
implemented, rsize was 512k; now that rsize=1M, this results in
readaheads of 15M, which cause all the traffic and lags.
next prev parent reply other threads:[~2019-09-21 8:00 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-19 7:29 rsize,wsize=1M causes severe lags in 10/100 Mbps, what sets those defaults? Alkis Georgopoulos
2019-09-19 15:08 ` Trond Myklebust
2019-09-19 15:58 ` rsize,wsize=1M causes severe lags in 10/100 Mbps Alkis Georgopoulos
2019-09-19 16:11 ` Trond Myklebust
2019-09-19 19:21 ` Alkis Georgopoulos
2019-09-19 19:51 ` Trond Myklebust
2019-09-19 19:57 ` Alkis Georgopoulos
2019-09-19 20:05 ` Trond Myklebust
2019-09-19 20:20 ` Alkis Georgopoulos
2019-09-19 20:40 ` Trond Myklebust
2019-09-19 21:19 ` Daniel Forrest
2019-09-19 21:42 ` Trond Myklebust
2019-09-19 22:16 ` Daniel Forrest
2019-09-20 9:25 ` Alkis Georgopoulos
2019-09-20 9:48 ` Alkis Georgopoulos
2019-09-20 10:04 ` Alkis Georgopoulos
2019-09-21 7:52 ` Alkis Georgopoulos
2019-09-21 7:59 ` Alkis Georgopoulos [this message]
2019-09-21 11:02 ` Alkis Georgopoulos
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