diff mbox

[1/2] PCI: Add mechanism to find topologically near cores

Message ID 1450864901-16712-1-git-send-email-daniel@numascale.com (mailing list archive)
State New, archived
Headers show

Commit Message

Daniel J Blueman Dec. 23, 2015, 10:01 a.m. UTC
Some devices (eg ixgbe) make assumptions about device to core locality when
specifying interrupts locality hints and allocate starting from core 0.
Moreover, interrupts may not be routable to distant NUMA nodes due to the
8-bit APIC ID space limitations.

Provide a mechanism drivers can use to find cores with reasonable locality
to a device; use the existing precendent of RECLAIM_DISTANCE (30), wrapping
the offset.

Signed-off-by: Daniel J Blueman <daniel@numascale.com>
---
 drivers/pci/pci.c   | 15 +++++++++++++++
 include/linux/pci.h |  1 +
 2 files changed, 16 insertions(+)

--
2.5.0

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Comments

kernel test robot Dec. 23, 2015, 10:35 a.m. UTC | #1
Hi Daniel,

[auto build test WARNING on pci/next]
[also build test WARNING on v4.4-rc6 next-20151223]

url:    https://github.com/0day-ci/linux/commits/Daniel-J-Blueman/PCI-Add-mechanism-to-find-topologically-near-cores/20151223-181947
base:   https://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci.git next
config: s390-allyesconfig (attached as .config)
reproduce:
        wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        make.cross ARCH=s390 

Note: it may well be a FALSE warning. FWIW you are at least aware of it now.

All warnings (new ones prefixed by >>):

   In file included from include/linux/smp.h:12:0,
                    from arch/s390/include/asm/spinlock.h:12,
                    from include/linux/spinlock.h:87,
                    from include/linux/rcupdate.h:38,
                    from include/linux/idr.h:18,
                    from include/linux/kernfs.h:14,
                    from include/linux/sysfs.h:15,
                    from include/linux/kobject.h:21,
                    from include/linux/of.h:21,
                    from drivers/pci/pci.c:13:
   drivers/pci/pci.c: In function 'cpu_near_dev':
>> include/linux/cpumask.h:174:9: warning: array subscript is below array bounds [-Warray-bounds]
     return find_first_bit(cpumask_bits(srcp), nr_cpumask_bits);
            ^

vim +174 include/linux/cpumask.h

da91309e Amir Vadai       2014-06-09  158  
2d3854a3 Rusty Russell    2008-11-05  159  #define for_each_cpu(cpu, mask)			\
2d3854a3 Rusty Russell    2008-11-05  160  	for ((cpu) = 0; (cpu) < 1; (cpu)++, (void)mask)
8bd93a2c Paul E. McKenney 2010-02-22  161  #define for_each_cpu_not(cpu, mask)		\
8bd93a2c Paul E. McKenney 2010-02-22  162  	for ((cpu) = 0; (cpu) < 1; (cpu)++, (void)mask)
2d3854a3 Rusty Russell    2008-11-05  163  #define for_each_cpu_and(cpu, mask, and)	\
2d3854a3 Rusty Russell    2008-11-05  164  	for ((cpu) = 0; (cpu) < 1; (cpu)++, (void)mask, (void)and)
2d3854a3 Rusty Russell    2008-11-05  165  #else
2d3854a3 Rusty Russell    2008-11-05  166  /**
2d3854a3 Rusty Russell    2008-11-05  167   * cpumask_first - get the first cpu in a cpumask
2d3854a3 Rusty Russell    2008-11-05  168   * @srcp: the cpumask pointer
2d3854a3 Rusty Russell    2008-11-05  169   *
2d3854a3 Rusty Russell    2008-11-05  170   * Returns >= nr_cpu_ids if no cpus set.
2d3854a3 Rusty Russell    2008-11-05  171   */
2d3854a3 Rusty Russell    2008-11-05  172  static inline unsigned int cpumask_first(const struct cpumask *srcp)
2d3854a3 Rusty Russell    2008-11-05  173  {
2d3854a3 Rusty Russell    2008-11-05 @174  	return find_first_bit(cpumask_bits(srcp), nr_cpumask_bits);
2d3854a3 Rusty Russell    2008-11-05  175  }
2d3854a3 Rusty Russell    2008-11-05  176  
2d3854a3 Rusty Russell    2008-11-05  177  /**
2d3854a3 Rusty Russell    2008-11-05  178   * cpumask_next - get the next cpu in a cpumask
2d3854a3 Rusty Russell    2008-11-05  179   * @n: the cpu prior to the place to search (ie. return will be > @n)
2d3854a3 Rusty Russell    2008-11-05  180   * @srcp: the cpumask pointer
2d3854a3 Rusty Russell    2008-11-05  181   *
2d3854a3 Rusty Russell    2008-11-05  182   * Returns >= nr_cpu_ids if no further cpus set.

:::::: The code at line 174 was first introduced by commit
:::::: 2d3854a37e8b767a51aba38ed6d22817b0631e33 cpumask: introduce new API, without changing anything

:::::: TO: Rusty Russell <rusty@rustcorp.com.au>
:::::: CC: Ingo Molnar <mingo@elte.hu>

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation
Bjorn Helgaas Dec. 23, 2015, 3:46 p.m. UTC | #2
Hi Daniel,

On Wed, Dec 23, 2015 at 06:01:40PM +0800, Daniel J Blueman wrote:
> Some devices (eg ixgbe) make assumptions about device to core locality when
> specifying interrupts locality hints and allocate starting from core 0.
> Moreover, interrupts may not be routable to distant NUMA nodes due to the
> 8-bit APIC ID space limitations.

The APIC ID issue is the primary problem you're trying to solve, but
this patch doesn't solve it directly because it doesn't look at
anything related to the APIC ID domain.  Anything you do here is a
guess that might work better, but it still won't necessarily work in
all cases.

Also, can you add a note about how this relates to the "call driver
probe function on node where device is attached" functionality in
pci_call_probe()?  It seems like that should be enough to keep us from
always allocating interrupts on core 0.  Maybe that's broken, or maybe
ixgbe isn't taking advantage of that?

> Provide a mechanism drivers can use to find cores with reasonable locality
> to a device; use the existing precendent of RECLAIM_DISTANCE (30), wrapping
> the offset.

I don't think it's a benefit to reuse RECLAIM_DISTANCE, because that
is a different concept that doesn't seem directly related to what
you're doing.  The name and the existing uses are related to memory
zone reclaiming, so I know I would be confused to see it also used for
IRQ assignment.

> Signed-off-by: Daniel J Blueman <daniel@numascale.com>
> ---
>  drivers/pci/pci.c   | 15 +++++++++++++++
>  include/linux/pci.h |  1 +
>  2 files changed, 16 insertions(+)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 314db8c..d5535d1 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -4833,6 +4833,22 @@ void __weak pci_fixup_cardbus(struct pci_bus *bus)
>  }
>  EXPORT_SYMBOL(pci_fixup_cardbus);
> 
> +int cpu_near_dev(const struct pci_dev *pdev, unsigned offset)

If this becomes a PCI interface, please add a "pci_" prefix to the
name.

The distance concept also applies to non-PCI devices, so ideally I
think a "pci_nearby_cpu()" or similar interface would be a wrapper
around a more generic interface that takes a "struct device *".

I don't really understand what the "offset" parameter is for.  It
looks like you're using it to spread across CPUs on a node, but that
seems like something that should be done internally to this interface.

> +{
> +	/* Start search from node device is on for optimal locality */
> +	int localnode = pcibus_to_node(pdev->bus);
> +	int cpu = cpumask_first(cpumask_of_node(localnode));
> +
> +	while (offset--) {
> +		do {
> +			cpu = (cpu + 1) % nr_cpu_ids;
> +		} while (!cpu_online(cpu) || node_distance(cpu_to_node(cpu),
> +			localnode) > RECLAIM_DISTANCE);
> +	}
> +
> +	return cpu;
> +}
> +
>  static int __init pci_setup(char *str)
>  {
>  	while (str) {
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 6ae25aa..f7491bd 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -842,6 +842,7 @@ void pci_stop_root_bus(struct pci_bus *bus);
>  void pci_remove_root_bus(struct pci_bus *bus);
>  void pci_setup_cardbus(struct pci_bus *bus);
>  void pci_sort_breadthfirst(void);
> +int cpu_near_dev(const struct pci_dev *pdev, unsigned offset);
>  #define dev_is_pci(d) ((d)->bus == &pci_bus_type)
>  #define dev_is_pf(d) ((dev_is_pci(d) ? to_pci_dev(d)->is_physfn : false))
>  #define dev_num_vf(d) ((dev_is_pci(d) ? pci_num_vf(to_pci_dev(d)) : 0))
> --
> 2.5.0
> 
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diff mbox

Patch

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 314db8c..d5535d1 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -4833,6 +4833,22 @@  void __weak pci_fixup_cardbus(struct pci_bus *bus)
 }
 EXPORT_SYMBOL(pci_fixup_cardbus);

+int cpu_near_dev(const struct pci_dev *pdev, unsigned offset)
+{
+	/* Start search from node device is on for optimal locality */
+	int localnode = pcibus_to_node(pdev->bus);
+	int cpu = cpumask_first(cpumask_of_node(localnode));
+
+	while (offset--) {
+		do {
+			cpu = (cpu + 1) % nr_cpu_ids;
+		} while (!cpu_online(cpu) || node_distance(cpu_to_node(cpu),
+			localnode) > RECLAIM_DISTANCE);
+	}
+
+	return cpu;
+}
+
 static int __init pci_setup(char *str)
 {
 	while (str) {
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 6ae25aa..f7491bd 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -842,6 +842,7 @@  void pci_stop_root_bus(struct pci_bus *bus);
 void pci_remove_root_bus(struct pci_bus *bus);
 void pci_setup_cardbus(struct pci_bus *bus);
 void pci_sort_breadthfirst(void);
+int cpu_near_dev(const struct pci_dev *pdev, unsigned offset);
 #define dev_is_pci(d) ((d)->bus == &pci_bus_type)
 #define dev_is_pf(d) ((dev_is_pci(d) ? to_pci_dev(d)->is_physfn : false))
 #define dev_num_vf(d) ((dev_is_pci(d) ? pci_num_vf(to_pci_dev(d)) : 0))