| Message ID | 20100420180112.1276.11906.stgit@ppwaskie-hc2.jf.intel.com |
|---|---|
| State | RFC, archived |
| Delegated to: | David Miller |
| Headers | show |
On Tue, 2010-04-20 at 11:01 -0700, Peter P Waskiewicz Jr wrote: > This patch adds a callback function pointer to the irq_desc > structure, along with a registration function and a read-only > proc entry for each interrupt. > > This affinity_hint handle for each interrupt can be used by > underlying drivers that need a better mechanism to control > interrupt affinity. The underlying driver can register a > callback for the interrupt, which will allow the driver to > provide the CPU mask for the interrupt to anything that > requests it. The intent is to extend the userspace daemon, > irqbalance, to help hint to it a preferred CPU mask to balance > the interrupt into. Doesn't it make more sense to have the driver follow affinity decisions made from user-space? I realise that reallocating queues is disruptive and we probably don't want irqbalance to trigger that, but there should be a mechanism for the administrator to trigger it. Looking at your patch for ixgbe: [...] > diff --git a/drivers/net/ixgbe/ixgbe_main.c > b/drivers/net/ixgbe/ixgbe_main.c > index 1b1419c..3e00d41 100644 > --- a/drivers/net/ixgbe/ixgbe_main.c > +++ b/drivers/net/ixgbe/ixgbe_main.c [...] > @@ -1083,6 +1113,16 @@ static void ixgbe_configure_msix(struct ixgbe_adapter *adapter) > q_vector->eitr = adapter->rx_eitr_param; > > ixgbe_write_eitr(q_vector); > + > + /* > + * Allocate the affinity_hint cpumask, assign the mask for > + * this vector, and register our affinity_hint callback. > + */ > + alloc_cpumask_var(&q_vector->affinity_mask, GFP_KERNEL); > + cpumask_set_cpu(v_idx, q_vector->affinity_mask); > + irq_register_affinity_hint(adapter->msix_entries[v_idx].vector, > + adapter, > + &ixgbe_irq_affinity_callback); > } > > if (adapter->hw.mac.type == ixgbe_mac_82598EB) [...] This just assigns IRQs to the first n CPU threads. Depending on the enumeration order, this might result in assigning an IRQ to each of 2 threads on a core while leaving other cores unused! irqbalance can already find the various IRQs associated with a single net device by looking at the handler names. So it can do at least as well as this without such a hint. Unless drivers have *useful* hints to give, I don't see the point in adding this mechanism. Ben.
On Wed, 21 Apr 2010, Ben Hutchings wrote: > On Tue, 2010-04-20 at 11:01 -0700, Peter P Waskiewicz Jr wrote: >> This patch adds a callback function pointer to the irq_desc >> structure, along with a registration function and a read-only >> proc entry for each interrupt. >> >> This affinity_hint handle for each interrupt can be used by >> underlying drivers that need a better mechanism to control >> interrupt affinity. The underlying driver can register a >> callback for the interrupt, which will allow the driver to >> provide the CPU mask for the interrupt to anything that >> requests it. The intent is to extend the userspace daemon, >> irqbalance, to help hint to it a preferred CPU mask to balance >> the interrupt into. > > Doesn't it make more sense to have the driver follow affinity decisions > made from user-space? I realise that reallocating queues is disruptive > and we probably don't want irqbalance to trigger that, but there should > be a mechanism for the administrator to trigger it. The driver here would be assisting userspace (irqbalance) to provide better details how the HW is laid out with respect to flows. As it stands today, irqbalance is almost guaranteed to move interrups to CPUs that are not aligned with where applications are running for network adapters. This is very apparent when running at speeds in the 10 Gigabit range, or even multiple 1 Gigabit ports running at the same time. > > Looking at your patch for ixgbe: > > [...] >> diff --git a/drivers/net/ixgbe/ixgbe_main.c >> b/drivers/net/ixgbe/ixgbe_main.c >> index 1b1419c..3e00d41 100644 >> --- a/drivers/net/ixgbe/ixgbe_main.c >> +++ b/drivers/net/ixgbe/ixgbe_main.c > [...] >> @@ -1083,6 +1113,16 @@ static void ixgbe_configure_msix(struct ixgbe_adapter *adapter) >> q_vector->eitr = adapter->rx_eitr_param; >> >> ixgbe_write_eitr(q_vector); >> + >> + /* >> + * Allocate the affinity_hint cpumask, assign the mask for >> + * this vector, and register our affinity_hint callback. >> + */ >> + alloc_cpumask_var(&q_vector->affinity_mask, GFP_KERNEL); >> + cpumask_set_cpu(v_idx, q_vector->affinity_mask); >> + irq_register_affinity_hint(adapter->msix_entries[v_idx].vector, >> + adapter, >> + &ixgbe_irq_affinity_callback); >> } >> >> if (adapter->hw.mac.type == ixgbe_mac_82598EB) > [...] > > This just assigns IRQs to the first n CPU threads. Depending on the > enumeration order, this might result in assigning an IRQ to each of 2 > threads on a core while leaving other cores unused! This ixgbe patch is only meant to be an example of how you could use it. I didn't hammer out all the corner cases of interrupt alignment in it yet. However, ixgbe is already aligning Tx flows onto the CPU/queue pair the Tx occurred (i.e. Tx session from CPU 4 will be queued on Tx queue 4), and then uses our Flow Director HW offload to steer Rx to Rx queue 4, assuming that the interrupt for Rx queue 4 is affinitized to CPU 4. The flow alignment breaks when the IRQ affinity has no knowledge what the underlying set of vectors are bound to, and what mode the HW is running in. FCoE offloads that spread multiple SCSI exchange IDs across CPU cores also needs this to properly align things. John Fastabend is going to provide some examples where this is very useful in the FCoE case. > irqbalance can already find the various IRQs associated with a single > net device by looking at the handler names. So it can do at least as > well as this without such a hint. Unless drivers have *useful* hints to > give, I don't see the point in adding this mechanism. irqbalance identifies which interrupts go with which network device. But it has no clue about flow management, and often will make a decision that hurts performance scaling. I have data showing when scaling multiple 10 Gigabit ports (4 in the current test), I can gain an extra 10 Gigabits of throughput just by aligning the interrupts properly (go from ~58 Gbps to ~68 Gbps in bi-directional tests). I do have the patches for irqbalance that uses this new handle to make better decisions for devices implementing the mask. I can send those to help show the whole picture of what's happening. Appreciate the feedback though Ben. Cheers, -PJ -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, 2010-04-22 at 05:11 -0700, Peter P Waskiewicz Jr wrote: > On Wed, 21 Apr 2010, Ben Hutchings wrote: > > > On Tue, 2010-04-20 at 11:01 -0700, Peter P Waskiewicz Jr wrote: > >> This patch adds a callback function pointer to the irq_desc > >> structure, along with a registration function and a read-only > >> proc entry for each interrupt. > >> > >> This affinity_hint handle for each interrupt can be used by > >> underlying drivers that need a better mechanism to control > >> interrupt affinity. The underlying driver can register a > >> callback for the interrupt, which will allow the driver to > >> provide the CPU mask for the interrupt to anything that > >> requests it. The intent is to extend the userspace daemon, > >> irqbalance, to help hint to it a preferred CPU mask to balance > >> the interrupt into. > > > > Doesn't it make more sense to have the driver follow affinity decisions > > made from user-space? I realise that reallocating queues is disruptive > > and we probably don't want irqbalance to trigger that, but there should > > be a mechanism for the administrator to trigger it. > > The driver here would be assisting userspace (irqbalance) to provide > better details how the HW is laid out with respect to flows. As it stands > today, irqbalance is almost guaranteed to move interrups to CPUs that are > not aligned with where applications are running for network adapters. > This is very apparent when running at speeds in the 10 Gigabit range, or > even multiple 1 Gigabit ports running at the same time. I'm well aware that irqbalance isn't making good decisions at the moment. The question is whether this will really help irqbalance to do better. [...] > > This just assigns IRQs to the first n CPU threads. Depending on the > > enumeration order, this might result in assigning an IRQ to each of 2 > > threads on a core while leaving other cores unused! > > This ixgbe patch is only meant to be an example of how you could use it. > I didn't hammer out all the corner cases of interrupt alignment in it yet. > However, ixgbe is already aligning Tx flows onto the CPU/queue pair the Tx > occurred (i.e. Tx session from CPU 4 will be queued on Tx queue 4), [...] OK, now I remember ixgbe has this odd select_queue() implementation. But this behaviour can result in reordering whenever a user thread migrates, and in any case Dave discourages people from setting select_queue(). So I see that these changes would be useful for ixgbe (together with an update to irqbalance), but they don't seem to fit the general direction of multiqueue networking on Linux. (Actually, the hints seem to be incomplete. If there are more than 16 CPU threads then multiple CPU threads can map to the same queues, but it looks like you only include the first in the queue's hint.) An alternate approach is to use the RX queue index to drive TX queue selection. I posted a patch to do that earlier this week. However I haven't yet had a chance to try that on a suitably large system. Ben.
Ben Hutchings wrote: > On Thu, 2010-04-22 at 05:11 -0700, Peter P Waskiewicz Jr wrote: >> On Wed, 21 Apr 2010, Ben Hutchings wrote: >> >>> On Tue, 2010-04-20 at 11:01 -0700, Peter P Waskiewicz Jr wrote: >>>> This patch adds a callback function pointer to the irq_desc >>>> structure, along with a registration function and a read-only >>>> proc entry for each interrupt. >>>> >>>> This affinity_hint handle for each interrupt can be used by >>>> underlying drivers that need a better mechanism to control >>>> interrupt affinity. The underlying driver can register a >>>> callback for the interrupt, which will allow the driver to >>>> provide the CPU mask for the interrupt to anything that >>>> requests it. The intent is to extend the userspace daemon, >>>> irqbalance, to help hint to it a preferred CPU mask to balance >>>> the interrupt into. >>> Doesn't it make more sense to have the driver follow affinity decisions >>> made from user-space? I realise that reallocating queues is disruptive >>> and we probably don't want irqbalance to trigger that, but there should >>> be a mechanism for the administrator to trigger it. >> The driver here would be assisting userspace (irqbalance) to provide >> better details how the HW is laid out with respect to flows. As it stands >> today, irqbalance is almost guaranteed to move interrups to CPUs that are >> not aligned with where applications are running for network adapters. >> This is very apparent when running at speeds in the 10 Gigabit range, or >> even multiple 1 Gigabit ports running at the same time. > > I'm well aware that irqbalance isn't making good decisions at the > moment. The question is whether this will really help irqbalance to do > better. > FCoE is one example where these hints can really help irqbalance make good decisions. By aligning the interrupt affinity with the FCoE receive processing thread we can avoid context switching from the NET_RX softirq to the receive processing thread. Because the base driver knows which rx rings are being used for FCoE in a particular configuration and their corresponding vectors it seems to be in the best position to provide good hints to irqbalance. Also if the mapping changes at some point the base driver will be aware of it. > [...] >>> This just assigns IRQs to the first n CPU threads. Depending on the >>> enumeration order, this might result in assigning an IRQ to each of 2 >>> threads on a core while leaving other cores unused! >> This ixgbe patch is only meant to be an example of how you could use it. >> I didn't hammer out all the corner cases of interrupt alignment in it yet. >> However, ixgbe is already aligning Tx flows onto the CPU/queue pair the Tx >> occurred (i.e. Tx session from CPU 4 will be queued on Tx queue 4), > [...] > > OK, now I remember ixgbe has this odd select_queue() implementation. > But this behaviour can result in reordering whenever a user thread > migrates, and in any case Dave discourages people from setting > select_queue(). So I see that these changes would be useful for ixgbe > (together with an update to irqbalance), but they don't seem to fit the > general direction of multiqueue networking on Linux. For DCB setting select_queue() is useful because we want to map traffic types to specific tx queues not hash them across all queues. In this case where we are placing specific traffic on specific queues it also makes sense to align the interrupts for some types such as FCoE. There shouldn't be any issues with user thread migration in this specific example. > > (Actually, the hints seem to be incomplete. If there are more than 16 > CPU threads then multiple CPU threads can map to the same queues, but it > looks like you only include the first in the queue's hint.) > > An alternate approach is to use the RX queue index to drive TX queue > selection. I posted a patch to do that earlier this week. However I > haven't yet had a chance to try that on a suitably large system. > I'll post an FCoE example patch soon and take a closer look at your patch, but mapping TX/RX queues in sock's won't help for cases like FCoE. Thanks, John. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h index 75f3f00..f2a7d0b 100644 --- a/include/linux/interrupt.h +++ b/include/linux/interrupt.h @@ -78,6 +78,8 @@ enum { }; typedef irqreturn_t (*irq_handler_t)(int, void *); +typedef unsigned int (*irq_affinity_hint_t)(cpumask_var_t, unsigned int, + void *); /** * struct irqaction - per interrupt action descriptor @@ -105,6 +107,18 @@ struct irqaction { unsigned long thread_flags; }; +/** + * struct irqaffinityhint - per interrupt affinity helper + * @callback: device driver callback function + * @dev: reference for the affected device + * @irq: interrupt number + */ +struct irqaffinityhint { + irq_affinity_hint_t callback; + void *dev; + int irq; +}; + extern irqreturn_t no_action(int cpl, void *dev_id); #ifdef CONFIG_GENERIC_HARDIRQS @@ -209,6 +223,9 @@ extern int irq_set_affinity(unsigned int irq, const struct cpumask *cpumask); extern int irq_can_set_affinity(unsigned int irq); extern int irq_select_affinity(unsigned int irq); +extern int irq_register_affinity_hint(unsigned int irq, void *dev, + irq_affinity_hint_t callback); +extern int irq_unregister_affinity_hint(unsigned int irq); #else /* CONFIG_SMP */ static inline int irq_set_affinity(unsigned int irq, const struct cpumask *m) @@ -223,6 +240,16 @@ static inline int irq_can_set_affinity(unsigned int irq) static inline int irq_select_affinity(unsigned int irq) { return 0; } +static inline int irq_register_affinity_hint(unsigned int irq, void *dev, + irq_affinity_hint_t callback) +{ + return -EINVAL; +} + +static inline int irq_unregister_affinity_hint(unsigned int irq); +{ + return -EINVAL; +} #endif /* CONFIG_SMP && CONFIG_GENERIC_HARDIRQS */ #ifdef CONFIG_GENERIC_HARDIRQS diff --git a/include/linux/irq.h b/include/linux/irq.h index 707ab12..bd73e9b 100644 --- a/include/linux/irq.h +++ b/include/linux/irq.h @@ -206,6 +206,7 @@ struct irq_desc { struct proc_dir_entry *dir; #endif const char *name; + struct irqaffinityhint *hint; } ____cacheline_internodealigned_in_smp; extern void arch_init_copy_chip_data(struct irq_desc *old_desc, diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c index 704e488..3674b6a 100644 --- a/kernel/irq/manage.c +++ b/kernel/irq/manage.c @@ -138,6 +138,42 @@ int irq_set_affinity(unsigned int irq, const struct cpumask *cpumask) return 0; } +int irq_register_affinity_hint(unsigned int irq, void *dev, + irq_affinity_hint_t callback) +{ + struct irq_desc *desc = irq_to_desc(irq); + unsigned long flags; + + raw_spin_lock_irqsave(&desc->lock, flags); + + if (!desc->hint) + desc->hint = kmalloc(sizeof(struct irqaffinityhint), + GFP_KERNEL); + desc->hint->callback = callback; + desc->hint->dev = dev; + desc->hint->irq = irq; + + raw_spin_unlock_irqrestore(&desc->lock, flags); + + return 0; +} +EXPORT_SYMBOL(irq_register_affinity_hint); + +int irq_unregister_affinity_hint(unsigned int irq) +{ + struct irq_desc *desc = irq_to_desc(irq); + unsigned long flags; + + raw_spin_lock_irqsave(&desc->lock, flags); + + kfree(desc->hint); + desc->hint = NULL; + + raw_spin_unlock_irqrestore(&desc->lock, flags); + + return 0; +} +EXPORT_SYMBOL(irq_unregister_affinity_hint); #ifndef CONFIG_AUTO_IRQ_AFFINITY /* * Generic version of the affinity autoselector. @@ -916,6 +952,9 @@ static struct irqaction *__free_irq(unsigned int irq, void *dev_id) desc->chip->disable(irq); } + /* make sure affinity_hint callback is cleaned up */ + kfree(desc->hint); + raw_spin_unlock_irqrestore(&desc->lock, flags); unregister_handler_proc(irq, action); diff --git a/kernel/irq/proc.c b/kernel/irq/proc.c index 7a6eb04..59110a3 100644 --- a/kernel/irq/proc.c +++ b/kernel/irq/proc.c @@ -32,6 +32,23 @@ static int irq_affinity_proc_show(struct seq_file *m, void *v) return 0; } +static int irq_affinity_hint_proc_show(struct seq_file *m, void *v) +{ + struct irq_desc *desc = irq_to_desc((long)m->private); + struct cpumask mask; + unsigned int ret = 0; + + if (desc->hint && desc->hint->callback) { + ret = desc->hint->callback(&mask, (long)m->private, + desc->hint->dev); + if (!ret) + seq_cpumask(m, &mask); + } + + seq_putc(m, '\n'); + return ret; +} + #ifndef is_affinity_mask_valid #define is_affinity_mask_valid(val) 1 #endif @@ -79,11 +96,23 @@ free_cpumask: return err; } +static ssize_t irq_affinity_hint_proc_write(struct file *file, + const char __user *buffer, size_t count, loff_t *pos) +{ + /* affinity_hint is read-only from proc */ + return -EOPNOTSUPP; +} + static int irq_affinity_proc_open(struct inode *inode, struct file *file) { return single_open(file, irq_affinity_proc_show, PDE(inode)->data); } +static int irq_affinity_hint_proc_open(struct inode *inode, struct file *file) +{ + return single_open(file, irq_affinity_hint_proc_show, PDE(inode)->data); +} + static const struct file_operations irq_affinity_proc_fops = { .open = irq_affinity_proc_open, .read = seq_read, @@ -92,6 +121,14 @@ static const struct file_operations irq_affinity_proc_fops = { .write = irq_affinity_proc_write, }; +static const struct file_operations irq_affinity_hint_proc_fops = { + .open = irq_affinity_hint_proc_open, + .read = seq_read, + .llseek = seq_lseek, + .release = single_release, + .write = irq_affinity_hint_proc_write, +}; + static int default_affinity_show(struct seq_file *m, void *v) { seq_cpumask(m, irq_default_affinity); @@ -231,6 +268,10 @@ void register_irq_proc(unsigned int irq, struct irq_desc *desc) /* create /proc/irq/<irq>/smp_affinity */ proc_create_data("smp_affinity", 0600, desc->dir, &irq_affinity_proc_fops, (void *)(long)irq); + + /* create /proc/irq/<irq>/affinity_hint */ + proc_create_data("affinity_hint", 0400, desc->dir, + &irq_affinity_hint_proc_fops, (void *)(long)irq); #endif proc_create_data("spurious", 0444, desc->dir,
This patch adds a callback function pointer to the irq_desc structure, along with a registration function and a read-only proc entry for each interrupt. This affinity_hint handle for each interrupt can be used by underlying drivers that need a better mechanism to control interrupt affinity. The underlying driver can register a callback for the interrupt, which will allow the driver to provide the CPU mask for the interrupt to anything that requests it. The intent is to extend the userspace daemon, irqbalance, to help hint to it a preferred CPU mask to balance the interrupt into. Signed-off-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com> --- include/linux/interrupt.h | 27 +++++++++++++++++++++++++++ include/linux/irq.h | 1 + kernel/irq/manage.c | 39 +++++++++++++++++++++++++++++++++++++++ kernel/irq/proc.c | 41 +++++++++++++++++++++++++++++++++++++++++ 4 files changed, 108 insertions(+), 0 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html