fcntl spinlock in Linux?

[Volker Lendecke]

On Wed, Jan 30, 2013 at 10:19:47AM -0500, J. Bruce Fields wrote:
> On Wed, Jan 30, 2013 at 03:25:27PM +0100, Volker Lendecke wrote:
> > On Wed, Jan 30, 2013 at 09:18:53AM -0500, J. Bruce Fields wrote:
> > > On Wed, Jan 30, 2013 at 08:32:47AM +0100, Volker Lendecke wrote:
> > > > On Tue, Jan 29, 2013 at 05:03:58PM -0500, J. Bruce Fields wrote:
> > > > > On Tue, Jan 29, 2013 at 10:51:33PM +0100, Volker Lendecke wrote:
> > > > > > On Tue, Jan 29, 2013 at 04:37:03PM -0500, J. Bruce Fields wrote:
> > > > > > > It's probably also easiest to fix.
> > > > > > 
> > > > > > Including deadlock detection? I guess this would have to
> > > > > > look at all locks held by a thread, possibly on different
> > > > > > inodes.
> > > > > 
> > > > > As a way of at least testing whether this is your problem, we could rip
> > > > > out the deadlock detection entirely.
> > > > 
> > > > Depending on the workload, this is partly Samba's problem.
> > > > Some real-world workloads imposed upon Samba make thousands
> > > > of smbds contend on a single lock.
> > > 
> > > By the way, do you have a way to boil any of these down into simple test
> > > cases that we could use?  (If it didn't even require installing Samba
> > > that would be ideal.)
> > 
> > I could send you a statically linked tdbtorture binary. It
> > is very easy to run that into the problems we are seeing.
> > Would that help?
> 
> Oh, well, if that's all it needs, I built tdbtorture here (just
> ./configure && make from samba git on an F16 machine).  Hm, now what do
> I do?:
> 
> 	# ./bin/tdbtorture -h
> 	Usage: tdbtorture [-t] [-k] [-n NUM_PROCS] [-l NUM_LOOPS] [-s SEED] [-H HASH_SIZE]
> 
> Any recommended commandline, or any data you could share with expected
> vs. actual results?

TDB_NO_FSYNC=1 time bin/tdbtorture -n 5000

and the load goes through the roof. Your mileage may vary
depending on your machine, number of cpus etc. As this is
essentially 5000 processes marching one behind another on
two hash chains, the ideal result would be something like 2
or so.

With best regards,

Volker Lendecke

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