Re: [REGRESSION] nfsd crashing with 3.6.0-rc7 on PowerPC

On Mon, 2012-10-01 at 16:03 +0200, Alexander Graf wrote:

Phew. Here we go :). It looks to be more of a PPC specific problem than it appeared as at first:

Ok, so I suspect the problem is the pushing down of the locks which
breaks with iommu backends that have a separate flush callback. In
that case, the flush moves out of the allocator lock.

Now we do call flush before we return, still, but it becomes racy
I suspect, but somebody needs to give it a closer look. I'm hoping
Anton or Nish will later today.

Cheers,
Ben.

b4c3a8729ae57b4f84d661e16a192f828eca1d03 is first bad commit
commit b4c3a8729ae57b4f84d661e16a192f828eca1d03
Author: Anton Blanchard [off-list ref]
Date:   Thu Jun 7 18:14:48 2012 +0000

    powerpc/iommu: Implement IOMMU pools to improve multiqueue adapter performance
    
    At the moment all queues in a multiqueue adapter will serialise
    against the IOMMU table lock. This is proving to be a big issue,
    especially with 10Gbit ethernet.
    
    This patch creates 4 pools and tries to spread the load across
    them. If the table is under 1GB in size we revert back to the
    original behaviour of 1 pool and 1 largealloc pool.
    
    We create a hash to map CPUs to pools. Since we prefer interrupts to
    be affinitised to primary CPUs, without some form of hashing we are
    very likely to end up using the same pool. As an example, POWER7
    has 4 way SMT and with 4 pools all primary threads will map to the
    same pool.
    
    The largealloc pool is reduced from 1/2 to 1/4 of the space to
    partially offset the overhead of breaking the table up into pools.
    
    Some performance numbers were obtained with a Chelsio T3 adapter on
    two POWER7 boxes, running a 100 session TCP round robin test.
    
    Performance improved 69% with this patch applied.
    
    Signed-off-by: Anton Blanchard [off-list ref]
    Signed-off-by: Benjamin Herrenschmidt [off-list ref]

:040000 040000 039ae3cbdcfded9c6b13e58a3fc67609f1b587b0 6755a8c4a690cc80dcf834d1127f21db925476d6 M	arch


Alex