On Thu, Jun 26, 2008 at 01:42:58PM -0400, Chuck Lever wrote: > On Jun 26, 2008, at 3:19 AM, Krishna Kumar2 wrote: >> Benny Halevy <bhalevy@xxxxxxxxxxx> wrote on 06/23/2008 06:10:40 PM: >> >>> Apparently the file is cached. You needed to restart nfs >>> and remount the file system to make sure it isn't before reading it. >>> Or, you can create a file larger than your host's cache size so >>> when you write (or read) it sequentially, its tail evicts its head >>> out of the cache. This is a less reliable method, yet creating a >>> file about 25% larger than the host's memory size should work for >>> you. >> >> I did a umount of all filesystems and restart NFS before testing. Here >> is the result: >> >> Local: >> Read: 69.5 MB/s >> Write: 70.0 MB/s >> NFS of same FS mounted loopback on same system: >> Read: 29.5 MB/s (57% drop) >> Write: 27.5 MB/s (60% drop) >> >> The drops seems exceedingly high. How can I figure out the source of >> the >> problem? Even if it is as general as to be able to state: "Problem is >> in >> the NFS client code" or "Problem is in the NFS server code", or >> "Problem >> can be mitigated by tuning" :-) > > It's hard to say what might be the problem just by looking at > performance results. > > You can look at client-side NFS and RPC performance metrics using some > prototype Python tools that were just added to nfs-utils. The scripts > themselves can be downloaded from: > > http://oss.oracle.com/~cel/Linux-2.6/2.6.25 > > but unfortunately they are not fully documented yet so you will have to > approach them with an open mind and a sense of experimentation. > > You can also capture network traces on your loopback interface to see if > there is, for example, unexpected congestion or latency, or if there are > other problems. > > But for loopback, the problem is often that the client and server are > sharing the same physical memory for caching data. Analyzing your test > system's physical memory utilization might be revealing. If he's just doing a single large read or write with cold caches (sounds like that's probably the case), then memory probably doesn't matter much, does it? --b. > > Otherwise, you should always expect some performance degradation when > comparing NFS and local disk. 50% is not completely unheard of. It's > the price paid for being able to share your file data concurrently among > multiple clients. > > -- > Chuck Lever > chuck[dot]lever[at]oracle[dot]com > -- > To unsubscribe from this list: send the line "unsubscribe linux-nfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
