Since there has been speculation about the throughput #s for lower end,
I have put up the comparison graph in the same page
(http://lse.sf.net/locking/dcache/dcache_lock.html).
As http://lse.sourceforge.net/locking/dcache/results/dbench/base+dc-tpt.png
would show, there is *no* performance degradation at the lower end or
UP. The absolute numbers are in
http://lse.sourceforge.net/locking/dcache/results/dbench/.
Thanks
Dipankar
-- Dipankar Sarma <dipankar@in.ibm.com> http://lse.sourceforge.net Linux Technology Center, IBM Software Lab, Bangalore, India.On Mon, Jan 21, 2002 at 05:40:39PM +0530, Maneesh Soni wrote: > Hi All, > > We have been doing experiments with dcache_lock to provide some relief from it. > Though dcache_lock is not a very hot lock in comparision to BKL but on higher > end machines it becomes quite contentious. We would like to have feedbacks, > comments about the approach taken and guidance on how to improve this further. > > As dcache_lock is acquired maximum number of times while doing lookup, the main > idea was to remove dcache_lock from d_lookup. With the help of Read Copy Update > it is possible to lookup the hash list of dentries without taking dcache_lock > but as d_lookup also updates the lru list, removing dcache_lock from d_lookup > was not straight forward. Various approaches were tried for that and the most > successful is doing lazy updation of lru list. > > Using this the dcache_lock contention was down from 16.5% to 0.95% on an > 8-way SMP box and lock utilization was down from 5.3% to 0.89% > > The patch for lazy lru updation using RCU can be found here: > > http://lse.sourceforge.net/locking/dcache/patches/2.4.17/dcache_rcu-lazy_lru-2.4.17-06.patch > > The basic conecpt for this approach is to not update the lru list in d_lookup > facilitating lockless d_lookup. The lru list can now have dentries with non zero > reference count also. The lru list is updated while pruning dentry cache. The > dcache_lock is kept around so that there are no changes in the update side > locking. > > The implementation details for lazy lru list updation and other approaches > can be found here: > > http://lse.sourceforge.net/locking/dcache/dcache_lock.html > > The above patch works fine with various file systems like ext2, JFS, ext3, /procand has been tested ok with ltp-20020108, dbench, httperf. And doesnot not have > any adverse effects on uni processor performance. > > > Regards, > Maneesh > > > -- > Maneesh Soni > IBM Linux Technology Center, > IBM India Software Lab, Bangalore. > Phone: +91-80-5044999 email: maneesh@in.ibm.com > http://lse.sourceforge.net/locking/rcupdate.html
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