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 <anton@xxxxxxxxx> > 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 <anton@xxxxxxxxx> > Signed-off-by: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> > > :040000 040000 039ae3cbdcfded9c6b13e58a3fc67609f1b587b0 6755a8c4a690cc80dcf834d1127f21db925476d6 M arch > > > Alex -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
