Re: [PATCH] PCI/VMD: Use local SRCU to prevent delaying global RCU

[Jon Derrick <jonathan.derrick@intel.com>]

Hi Bjorn,

I need to attach a patch which selects SRCU in the Kconfig. Do you want
this and the original patch as a new set or should I just send this new
Kconfig patch?

On Fri, Nov 11, 2016 at 03:07:25PM -0600, Bjorn Helgaas wrote:
> 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@intel.com>
> 
> 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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