On Fri, 2012-07-20 at 15:41 -0700, Nishanth Aravamudan wrote: > Ping on this ... we've tripped the same issue on a different system, it > would appear. Would appreciate if anyone can provide answers to the > questions below.
Well, I haven't hit it but your description makes sense. Why not use dma_alloc_coherent though ? Rather than kmalloc followed by map ? At least on power we give you page alignment for these, so the problem is solved magically :-) Another option is GFP + dma_map_page which is roughly equivalent. If you think it's a waste of space based on the queue size, then just add an extra pointer, I wouldn't bother with a cache for something only allocated when the driver initializes. Cheers, Ben. > Thanks, > Nish > > On 15.05.2012 [10:01:41 -0700], Nishanth Aravamudan wrote: > > Hi Santiago, > > > > Are you still working on ibmveth? > > > > I've found a very sporadic bug with ibmveth in some testing. PAPR > > requires that: > > > > "Validate the Buffer Descriptor of the receive queue buffer (I/O > > addresses for entire buffer length starting at the spec- ified I/O > > address are translated by the RTCE table, length is a multiple of 16 > > bytes, and alignment is on a 16 byte boundary) else H_Parameter." > > > > but from what I can tell ibmveth.c is not enforcing this last condition: > > > > adapter->rx_queue.queue_addr = > > kmalloc(adapter->rx_queue.queue_len, GFP_KERNEL); > > > > ... > > > > adapter->rx_queue.queue_dma = dma_map_single(dev, > > adapter->rx_queue.queue_addr, adapter->rx_queue.queue_len, > > DMA_BIDIRECTIONAL); > > > > ... > > > > rxq_desc.fields.address = adapter->rx_queue.queue_dma; > > > > ... > > > > > > lpar_rc = ibmveth_register_logical_lan(adapter, rxq_desc, > > mac_address); > > netdev_err(netdev, "buffer TCE:0x%llx filter TCE:0x%llx rxq " > > "desc:0x%llx MAC:0x%llx\n", adapter->buffer_list_dma, > > adapter->filter_list_dma, rxq_desc.desc, mac_address); > > > > And I got on one install attempt: > > > > [ 39.978430] ibmveth 30000004: eth0: h_register_logical_lan failed with -4 > > [ 39.978449] ibmveth 30000004: eth0: buffer TCE:0x1000 filter TCE:0x10000 > > rxq desc:0x80006010000200a8 MAC:0x56754de8e904 > > > > rxq desc, as you can see is not 16byte aligned. kmalloc() only > > guarantees 8-byte alignment (as does gcc, I think). Initially, I thought > > we could just overallocate the queue_addr and ALIGN() down, but then we > > would need to save the original kmalloc pointer in a new struct member > > per rx_queue. > > > > So a couple of questions: > > > > 1) Is my analysis accurate? :) > > > > 2) How gross would it be to save an extra pointer for every rx_queue? > > > > 3) Based upon 2), is it better to just go ahead and create our own > > kmem_cache (which gets an alignment specified)? > > > > For 3), I started coding this, but couldn't find a clean place to > > allocate the kmem_cache itself, as the size of each object depends on > > the run-time characteristics (afaict), but needs to be specified at > > cache creation time. Any insight you could provide would be great! > > > > Thanks, > > Nish > > > > -- > > Nishanth Aravamudan <n...@us.ibm.com> > > IBM Linux Technology Center > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
