On Thu, Oct 06, 2016 at 04:47:42PM -0600, Jon Derrick wrote:
> SRCU lets synchronize_srcu depend on VMD-local RCU primitives,
> preventing long delays from locking up RCU in other systems. VMD
> performs a synchronize when removing a device, but will hit all irq
> lists if the device uses all VMD vectors. This patch will not help VMD's
> RCU synchronization, but will isolate the read side delays to the VMD
> subsystem. Additionally, the use of SRCU in VMD's isr will keep it
> isolated from any other RCU waiters in the rest of the system.
>
> The patch was tested using concurrent fio and nvme resets:
> [global]
> rw=read
> bs=4k
> direct=1
> ioengine=libaio
> iodepth=32
> norandommap
> timeout=300
> runtime=1000000000
>
> [nvme0]
> cpus_allowed=0-63
> numjobs=8
> filename=/dev/nvme0n1
>
> [nvme1]
> cpus_allowed=0-63
> numjobs=8
> filename=/dev/nvme1n1
>
> while (true) do
> for i in /sys/class/nvme/nvme*; do
> echo "Resetting ${i##*/}"
> echo 1 > $i/reset_controller;
> sleep 5
> done;
> done
>
> Signed-off-by: Jon Derrick <jonathan.derrick@xxxxxxxxx>
Keith? I wait for your ack before applying VMD changes.
> ---
> Applies to pci/host-vmd with cherry-pick:
> 21c80c9fefc3db10b530a96eb0478c29eb28bf77 x86/PCI: VMD: Fix infinite loop
> executing irq's
>
>
> drivers/pci/host/vmd.c | 26 ++++++++++++++++++++------
> 1 file changed, 20 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/pci/host/vmd.c b/drivers/pci/host/vmd.c
> index 5705852..6bd57ee 100644
> --- a/drivers/pci/host/vmd.c
> +++ b/drivers/pci/host/vmd.c
> @@ -19,6 +19,7 @@
> #include <linux/module.h>
> #include <linux/msi.h>
> #include <linux/pci.h>
> +#include <linux/srcu.h>
> #include <linux/rculist.h>
> #include <linux/rcupdate.h>
>
> @@ -39,7 +40,6 @@ static DEFINE_RAW_SPINLOCK(list_lock);
> /**
> * struct vmd_irq - private data to map driver IRQ to the VMD shared vector
> * @node: list item for parent traversal.
> - * @rcu: RCU callback item for freeing.
> * @irq: back pointer to parent.
> * @enabled: true if driver enabled IRQ
> * @virq: the virtual IRQ value provided to the requesting driver.
> @@ -48,7 +48,6 @@ static DEFINE_RAW_SPINLOCK(list_lock);
> */
> struct vmd_irq {
> struct list_head node;
> - struct rcu_head rcu;
> struct vmd_irq_list *irq;
> bool enabled;
> unsigned int virq;
> @@ -56,11 +55,13 @@ struct vmd_irq {
> /**
> * struct vmd_irq_list - list of driver requested IRQs mapping to a VMD vector
> * @irq_list: the list of irq's the VMD one demuxes to.
> + * @srcu: SRCU struct for local synchronization.
> * @count: number of child IRQs assigned to this vector; used to track
> * sharing.
> */
> struct vmd_irq_list {
> struct list_head irq_list;
> + struct srcu_struct srcu;
> unsigned int count;
> };
>
> @@ -218,14 +219,14 @@ static void vmd_msi_free(struct irq_domain *domain,
> struct vmd_irq *vmdirq = irq_get_chip_data(virq);
> unsigned long flags;
>
> - synchronize_rcu();
> + synchronize_srcu(&vmdirq->irq->srcu);
>
> /* XXX: Potential optimization to rebalance */
> raw_spin_lock_irqsave(&list_lock, flags);
> vmdirq->irq->count--;
> raw_spin_unlock_irqrestore(&list_lock, flags);
>
> - kfree_rcu(vmdirq, rcu);
> + kfree(vmdirq);
> }
>
> static int vmd_msi_prepare(struct irq_domain *domain, struct device *dev,
> @@ -639,11 +640,12 @@ static irqreturn_t vmd_irq(int irq, void *data)
> {
> struct vmd_irq_list *irqs = data;
> struct vmd_irq *vmdirq;
> + int idx;
>
> - rcu_read_lock();
> + idx = srcu_read_lock(&irqs->srcu);
> list_for_each_entry_rcu(vmdirq, &irqs->irq_list, node)
> generic_handle_irq(vmdirq->virq);
> - rcu_read_unlock();
> + srcu_read_unlock(&irqs->srcu, idx);
>
> return IRQ_HANDLED;
> }
> @@ -689,6 +691,10 @@ static int vmd_probe(struct pci_dev *dev, const struct pci_device_id *id)
> return -ENOMEM;
>
> for (i = 0; i < vmd->msix_count; i++) {
> + err = init_srcu_struct(&vmd->irqs[i].srcu);
> + if (err)
> + return err;
> +
> INIT_LIST_HEAD(&vmd->irqs[i].irq_list);
> err = devm_request_irq(&dev->dev, pci_irq_vector(dev, i),
> vmd_irq, 0, "vmd", &vmd->irqs[i]);
> @@ -707,11 +713,19 @@ static int vmd_probe(struct pci_dev *dev, const struct pci_device_id *id)
> return 0;
> }
>
> +static void vmd_cleanup_srcu(struct vmd_dev *vmd)
> +{
> + int i;
> + for (i = 0; i < vmd->msix_count; i++)
> + cleanup_srcu_struct(&vmd->irqs[i].srcu);
> +}
> +
> static void vmd_remove(struct pci_dev *dev)
> {
> struct vmd_dev *vmd = pci_get_drvdata(dev);
>
> vmd_detach_resources(vmd);
> + vmd_cleanup_srcu(vmd);
> pci_set_drvdata(dev, NULL);
> sysfs_remove_link(&vmd->dev->dev.kobj, "domain");
> pci_stop_root_bus(vmd->bus);
> --
> 1.8.3.1
>
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