[+cc Rusty] On Mon, Jun 24, 2013 at 2:05 PM, Alexander Duyck <alexander.h.duyck@xxxxxxxxx> wrote: > This patch is meant to address the fact that we are making unnecessary calls > to work_on_cpu. To resolve this I have added a check to see if the current > node is the correct node for the device before we decide to assign the probe > task to another CPU. > > The advantages to this approach is that we can avoid reentrant calls to > work_on_cpu. In addition we should not make any calls to setup the work > remotely in the case of a single node system that has NUMA enabled. The description above makes it sound like this is just a minor performance enhancement, but I think the real reason you want this is to resolve the lockdep warning mentioned at [1]. That thread is long and confusing, so I'd like to see a bugzilla that distills out the useful details, and a synopsis in this changelog. [1] https://lkml.kernel.org/r/1368498506-25857-7-git-send-email-yinghai@xxxxxxxxxx > Signed-off-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxx> > --- > > This patch is based off of work I submitted in an earlier patch that I never > heard back on. The change was originally submitted in: > pci: Avoid reentrant calls to work_on_cpu > > I'm not sure what ever happened with that patch, however after reviewing it > some myself I decided I could do without the change to the comments since they > were unneeded. As such I am resubmitting this as a much simpler patch that > only adds the line of code needed to avoid calling work_on_cpu for every call > to probe on an NUMA node specific device. > > drivers/pci/pci-driver.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c > index 79277fb..7d81713 100644 > --- a/drivers/pci/pci-driver.c > +++ b/drivers/pci/pci-driver.c > @@ -282,7 +282,7 @@ static int pci_call_probe(struct pci_driver *drv, struct pci_dev *dev, > its local memory on the right node without any need to > change it. */ > node = dev_to_node(&dev->dev); > - if (node >= 0) { > + if ((node >= 0) && (node != numa_node_id())) { > int cpu; > > get_online_cpus(); I think it's theoretically unsafe to use numa_node_id() while preemption is enabled. It seems a little strange to me that this "run the driver probe method on the correct node" code is in PCI. I would think this behavior would be desirable for *all* bus types, not just PCI, so maybe it would make sense to do this up in device_attach() or somewhere similar. But Rusty added this (in 873392ca51), and he knows way more about this stuff than I do. Bjorn -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
