> -----Original Message-----
> From: Robin Murphy [mailto:robin.mur...@arm.com]
> Sent: Tuesday, June 2, 2020 1:14 AM
> To: Song Bao Hua (Barry Song) <song.bao....@hisilicon.com>; w...@kernel.org;
> h...@lst.de; m.szyprow...@samsung.com; iommu@lists.linux-foundation.org
> Cc: Linuxarm <linux...@huawei.com>; linux-arm-ker...@lists.infradead.org
> Subject: Re: [PATCH] iommu/arm-smmu-v3: expose numa_node attribute to
> users in sysfs
>
> On 2020-05-30 10:15, Barry Song wrote:
> > As tests show the latency of dma_unmap can increase dramatically while
> > calling them cross NUMA nodes, especially cross CPU packages, eg.
> > 300ns vs 800ns while waiting for the completion of CMD_SYNC in an
> > empty command queue. The large latency causing by remote node will
> > in turn make contention of the command queue more serious, and enlarge
> > the latency of DMA users within local NUMA nodes.
> >
> > Users might intend to enforce NUMA locality with the consideration of
> > the position of SMMU. The patch provides minor benefit by presenting
> > this information to users directly, as they might want to know it without
> > checking hardware spec at all.
>
> Hmm, given that dev-to_node() is a standard driver model thing, is there
> not already some generic device property that can expose it - and if
> not, should there be? Presumably if userspace cares enough to want to
> know whereabouts in the system an IOMMU is, it probably also cares where
> the actual endpoint devices are too.
>
> At the very least, it doesn't seem right for it to be specific to one
> single IOMMU driver.
Right now pci devices have generally got the numa_node in sysfs by
drivers/pci/pci-sysfs.c
static ssize_t numa_node_store(struct device *dev,
struct device_attribute *attr, const char *buf,
size_t count)
{
...
add_taint(TAINT_FIRMWARE_WORKAROUND, LOCKDEP_STILL_OK);
pci_alert(pdev, FW_BUG "Overriding NUMA node to %d. Contact your
vendor for updates.",
node);
dev->numa_node = node;
return count;
}
static ssize_t numa_node_show(struct device *dev, struct device_attribute *attr,
char *buf)
{
return sprintf(buf, "%d\n", dev->numa_node);
}
static DEVICE_ATTR_RW(numa_node);
for other devices who care about numa information, the specific drivers are
doing that, for example:
drivers/dax/bus.c: if (a == &dev_attr_numa_node.attr &&
!IS_ENABLED(CONFIG_NUMA))
drivers/dax/bus.c: &dev_attr_numa_node.attr,
drivers/dma/idxd/sysfs.c: &dev_attr_numa_node.attr,
drivers/hv/vmbus_drv.c: &dev_attr_numa_node.attr,
drivers/nvdimm/bus.c: &dev_attr_numa_node.attr,
drivers/nvme/host/core.c: &dev_attr_numa_node.attr,
smmu is usually a platform device, we can actually expose numa_node for
platform_device, or globally expose numa_node
for general "device" if people don't opposite.
Barry
>
> Robin.
>
> > Signed-off-by: Barry Song <song.bao....@hisilicon.com>
> > ---
> > drivers/iommu/arm-smmu-v3.c | 40
> ++++++++++++++++++++++++++++++++++++-
> > 1 file changed, 39 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
> > index 82508730feb7..754c4d59498b 100644
> > --- a/drivers/iommu/arm-smmu-v3.c
> > +++ b/drivers/iommu/arm-smmu-v3.c
> > @@ -4021,6 +4021,44 @@ err_reset_pci_ops: __maybe_unused;
> > return err;
> > }
> >
> > +static ssize_t numa_node_show(struct device *dev,
> > + struct device_attribute *attr, char *buf)
> > +{
> > + return sprintf(buf, "%d\n", dev_to_node(dev));
> > +}
> > +static DEVICE_ATTR_RO(numa_node);
> > +
> > +static umode_t arm_smmu_numa_attr_visible(struct kobject *kobj, struct
> attribute *a,
> > + int n)
> > +{
> > + struct device *dev = container_of(kobj, typeof(*dev), kobj);
> > +
> > + if (!IS_ENABLED(CONFIG_NUMA))
> > + return 0;
> > +
> > + if (a == &dev_attr_numa_node.attr &&
> > + dev_to_node(dev) == NUMA_NO_NODE)
> > + return 0;
> > +
> > + return a->mode;
> > +}
> > +
> > +static struct attribute *arm_smmu_dev_attrs[] = {
> > + &dev_attr_numa_node.attr,
> > + NULL
> > +};
> > +
> > +static struct attribute_group arm_smmu_dev_attrs_group = {
> > + .attrs = arm_smmu_dev_attrs,
> > + .is_visible = arm_smmu_numa_attr_visible,
> > +};
> > +
> > +
> > +static const struct attribute_group *arm_smmu_dev_attrs_groups[] = {
> > + &arm_smmu_dev_attrs_group,
> > + NULL,
> > +};
> > +
> > static int arm_smmu_device_probe(struct platform_device *pdev)
> > {
> > int irq, ret;
> > @@ -4097,7 +4135,7 @@ static int arm_smmu_device_probe(struct
> platform_device *pdev)
> > return ret;
> >
> > /* And we're up. Go go go! */
> > - ret = iommu_device_sysfs_add(&smmu->iommu, dev, NULL,
> > + ret = iommu_device_sysfs_add(&smmu->iommu, dev,
> arm_smmu_dev_attrs_groups,
> > "smmu3.%pa", &ioaddr);
> > if (ret)
> > return ret;
> >
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