On Dec 20, 2007 12:20 +0200, Alex Lyashkov wrote: > On Thu, 2007-12-13 at 17:21 -0700, Andreas Dilger wrote: > > Well, we already have a beginning of this kind of operation on the client > > with client-side metadata statahead. That detects readdir->stat operation > > and prefetches the MDS attribute data. > > I'm not sure this was good idea. stat readahead is slow for single cpu > box, and slow in testing with local devices (very low network latency) - > and can add noticeable speedup only with high latency network links, > because can send many stats requests when main thread block in waiting > one answer.
This isn't the common configuration that we run in, however. Most Lustre setups today (and even laptops) have multiple CPUs, and clients are generally remote instead of local. In such testing the statahead is about 2x faster than without, and I think it could be even faster if we also had OST statahead. The current statahead is limited by the fact we are only hiding the client->MDS latency (1 of 2 synchronous RPCs) and not the client->OSTs latency (which happen concurrently for N stripes, but will be the slowest of all OST getattrs). So our maximum "ls -l" improvement is currently 2x until SOM (for closed files) or OST statahead is implemented. Cheers, Andreas -- Andreas Dilger Sr. Staff Engineer, Lustre Group Sun Microsystems of Canada, Inc. _______________________________________________ Lustre-devel mailing list [email protected] https://mail.clusterfs.com/mailman/listinfo/lustre-devel
