Re: why is NFS performance poor when decompress linux kernel

From: Xin Zhao
Date: Sat Oct 08 2005 - 09:35:34 EST

I think the stat might be one reason. cuz when I do 'nfsstat', I
noticed that "getattr" and "setattr" are executed about 40000 times
while other operations are executed for less than 10000 times. That
gave me a feeling that some optimization can be considered to reduce
the getattr and setattr requests.

async and sync options affect write performance on large files more
significantly. But decompress kernel involves a lot of small files.
Because nfs will force data sync to disk before file close. async and
sync do not behave quite different.

Anyone has exeprience with NFS4? I don't know whether it improves in this parts


On 10/8/05, Willy Tarreau <willy@xxxxxxxxx> wrote:
> Hi,
> On Sat, Oct 08, 2005 at 01:59:48AM -0400, Lee Revell wrote:
> > On Sat, 2005-10-08 at 00:39 -0400, Xin Zhao wrote:
> > > I noticed that when doing large file copy or linux kernel compilation
> > > in a NFS direcotry, the performance is not bad compared to local disk
> > > filesystem such as ext2. However, if I do linux kernel tarball
> > > decompression on a NFS directory, the performance is much worse than
> > > local disk filesystem (over 3 times slower). Anybody know the reason?
> >
> > Because NFS requires all writes to be synchronous by default, and
> > uncompressing the kernel is the most write intensive of those three
> > operations. Mount with the async option and the performance should be
> > closer to a local disk. Obviously this is more dangerous.
> I don't agree with you, Lee. My NFS is mounted with async by default,
> and what takes the most time when extracting a kernel archive is that
> tar does a stat() on every file before writing it. And THAT stat()
> prevents writes from being buffered. A better solution might be to
> process several files in parallel (multi-process/multi-thread).
> Perhaps a project for a new tar ?
> Just for a test, I tried extracting multiple files in parallel. The
> method is completely crappy, but I could saturate my NFS server this
> way :
> $ tar ztf /tmp/linux-2.6.9.tar.gz >/tmp/file-list
> $ sed -n '1~4p' < /tmp/file-list >/tmp/file-list1
> $ sed -n '2~4p' < /tmp/file-list >/tmp/file-list2
> $ sed -n '3~4p' < /tmp/file-list >/tmp/file-list3
> $ sed -n '4~4p' < /tmp/file-list >/tmp/file-list4
> $ tar zxf /tmp/linux-2.6.9.tar.gz -T /tmp/file-list1 & tar zxf /tmp/linux-2.6.9.tar.gz -T /tmp/file-list2 & tar zxf /tmp/linux-2.6.9.tar.gz -T /tmp/file-list3 & tar zxf /tmp/linux-2.6.9.tar.gz -T /tmp/file-list4 & wait
> OK, it finally took more time, although the server was saturated (maybe
> it crawled under seeks at the end, I did not check). This may constitute
> a starting point for people having more time to research in this area.
> > Lee
> Cheers,
> Willy
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