Re: RCU scaling on large systems

[Andrea Arcangeli]

On Sat, May 01, 2004 at 02:17:04PM -0700, William Lee Irwin III wrote:
> On Sat, May 01, 2004 at 07:08:05AM -0500, Jack Steiner wrote:
> > On a 512p idle 2.6.5 system, each cpu spends ~6% of the time in the kernel
> > RCU code. The time is spent contending for shared cache lines.
> 
> Would something like this help cacheline contention? This uses the
> per_cpu data areas to hold per-cpu booleans for needing switches.
> Untested/uncompiled.
> 
> The global lock is unfortunately still there.

I'm afraid this cannot help, the rcu_cpu_mask and the mutex are in the same
cacheline, so it's not just about the global lock being still there,
it's about the cpumask being in the same cacheline with the global lock.
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