Re: [patch/rfc/rft] sd: allocate request_queue on device's localnuma node

From: Bart Van Assche
Date: Tue Oct 23 2012 - 02:45:25 EST

On 10/22/12 21:01, Jeff Moyer wrote:
All of the infrastructure is available to allocate a request_queue on a
particular numa node, but it isn't being utilized at all. Wire up the
sd driver to allocate the request_queue on the HBA's local numa node.

This is a request for comments and testing (I've built and booted it,
nothing more). I believe that this should be a performance win, but I
have no numbers to back it up as yet. Suggestions for workloads to test
are welcome.


Signed-off-by: Jeff Moyer <jmoyer@xxxxxxxxxx>

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index da36a3a..7986483 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1664,7 +1664,8 @@ struct request_queue *__scsi_alloc_queue(struct Scsi_Host *shost,
struct request_queue *q;
struct device *dev = shost->dma_dev;

- q = blk_init_queue(request_fn, NULL);
+ q = blk_init_queue_node(request_fn, NULL,
+ dev_to_node(&shost->shost_dev));
if (!q)
return NULL;

Are you sure this approach will always result in the queue being allocated on the same NUMA node as the HCA ? If e.g. a user triggers LUN scanning via sysfs the above code may be invoked on another NUMA node than the node to which the HCA is connected. Also, if you have a look at e.g. scsi_request_fn() or scsi_device_unbusy() you will see that in order to avoid inter-node traffic it's important to allocate the sdev and shost data structures on the same NUMA node. How about the following approach ?
- Add a variant of scsi_host_alloc() that allows to specify on which
NUMA node to allocate the shost structure and also that stores the
identity of that node in the shost structure.
- Modify __scsi_alloc_queue() such that it allocates the sdev structure
on the same NUMA node as the shost structure.
- Modify the SCSI LLD of your choice such that it uses the new
scsi_host_alloc() call. According to what is appropriate the NUMA node
on which to allocate the shost could be specified by the user or could
be identical to the NUMA node of the HCA controlled by the SCSI LLD
(see e.g. /sys/devices/pci*/*/numa_node). Please keep in mind that a
single PCIe bus may have a minimal distance to more than one NUMA
node. See e.g. the diagram at the top of page 8 in
for a system diagram of a NUMA system where each PCIe bus has a
minimal distance to two different NUMA nodes.

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