Re: Scalability requirements for sysv ipc (+namespaces broken withSEM_UNDO)

[Nadia Derbey]

Nadia Derbey wrote:
> Mike Galbraith wrote:
>
> > On Sun, 2008-03-30 at 16:12 +0200, Manfred Spraul wrote:
> >
> > > Mike Galbraith wrote:
> > >
> > > > On Sat, 2008-03-22 at 20:08 +0100, Manfred Spraul wrote:
> > > >
> > > >  
> > > >
> > > > > just the normal performance of 2.6.25-rc3 is abyssimal, 55 to 60% 
> > > > > slower than 2.6.18.8:
> > > > >    
> > > >
> > > >
> > > > After manually reverting 3e148c79938aa39035669c1cfa3ff60722134535,
> > > > 2.6.25.git scaled linearly
> > >
> > >
> > > We can't just revert that patch: with IDR, a global lock is mandatory 
> > > :-(
> > > We must either revert the whole idea of using IDR or live with the 
> > > reduced scalability.
> >
> >
> >
> > Yeah, I looked at the problem, but didn't know what the heck to do about
> > it, so just grabbed my axe to verify/quantify.
> >
> >
> > > Actually, there are further bugs: the undo structures are not 
> > > namespace-aware, thus semop with SEM_UNDO, unshare, create new array 
> > > with same id, but more semaphores, another semop with SEM_UNDO will 
> > > corrupt kernel memory :-(
> > > I'll try to clean up the bugs first, then I'll look at the 
> > > scalability again.
> >
> >
> >
> > Great!
> >
> >     -Mike
>
> I could get better results with the following solution:
> wrote an RCU-based idr api (layers allocation is managed similarly to 
> the radix-tree one)
>
> Using it in the ipc code makes me get rid of the read lock taken in 
> ipc_lock() (the one introduced in 
> 3e148c79938aa39035669c1cfa3ff60722134535).
>
> You'll find the results in attachment (kernel is 2.6.25-rc3-mm1).
> output.25_rc3_mm1.ref.8  --> pmsg output for the 2.6.25-rc3-mm1
> plot.25_rc3_mm1.ref.8    --> previous file results for use by gnuplot
> output.25_rc3_mm1.ridr.8 --> pmsg output for the 2.6.25-rc3-mm1
>                              + rcu-based idrs
> plot.25_rc3_mm1.ridr.8   --> previous file results for use by gnuplot
>
>
> I think I should be able to send a patch next week. It is presently an 
> uggly code: I copied idr.c and idr.h into ridr.c and ridr.h to go fast, 
> so didn't do any code factorization.
>
> Regards
> Nadia

Sorry forgot the command:

for i in 1 2 3 4 5 6 7 8;do ./pmsg $i 5;done > output.25_rc3_mm1.ref.8


Regards,
Nadia

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