[+cc linux-pci]
On Thu, Mar 16, 2017 at 10:50:06PM +0100, Thomas Gleixner wrote:
> The generic pci configuration space accessors are globally serialized via
> pci_lock. On larger systems this causes massive lock contention when the
> configuration space has to be accessed frequently. One such access pattern
> is the Intel Uncore performance counter unit.
s/pci/PCI/ above.
> Provide a kernel config option which can be selected by an architecture
> when the low level PCI configuration space accessors in the architecture
> use their own serialization or can operate completely lockless.
The arch/x86/pci/common.c comment:
/*
* This interrupt-safe spinlock protects all accesses to PCI
* configuration space.
*/
DEFINE_RAW_SPINLOCK(pci_config_lock);
is no longer quite correct.
I think the raw_pci_read() and raw_pci_write() implementations are
such that we use the old locked accessors for the first 256 bytes,
even when ECAM is available. Not necessarily a problem, just an
observation. I guess the uncore PMU registers are in the extended
config space.
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> ---
> drivers/pci/Kconfig | 3 +++
> drivers/pci/access.c | 16 ++++++++++++----
> 2 files changed, 15 insertions(+), 4 deletions(-)
>
> --- a/drivers/pci/Kconfig
> +++ b/drivers/pci/Kconfig
> @@ -86,6 +86,9 @@ config PCI_ATS
> config PCI_ECAM
> bool
>
> +config PCI_LOCKLESS_CONFIG
> + bool
It's conceivable that this could be a per-host bridge property, but
not worth worrying about for now.
> config PCI_IOV
> bool "PCI IOV support"
> depends on PCI
> --- a/drivers/pci/access.c
> +++ b/drivers/pci/access.c
> @@ -25,6 +25,14 @@ DEFINE_RAW_SPINLOCK(pci_lock);
> #define PCI_word_BAD (pos & 1)
> #define PCI_dword_BAD (pos & 3)
>
> +#ifdef CONFIG_PCI_LOCKLESS_CONFIG
> +# define pci_lock_config(f) do { (void)(f); } while (0)
> +# define pci_unlock_config(f) do { (void)(f); } while (0)
> +#else
> +# define pci_lock_config(f) raw_spin_lock_irqsave(&pci_lock, f)
> +# define pci_unlock_config(f) raw_spin_unlock_irqrestore(&pci_lock, f)
> +#endif
> +
> #define PCI_OP_READ(size, type, len) \
> int pci_bus_read_config_##size \
> (struct pci_bus *bus, unsigned int devfn, int pos, type *value) \
> @@ -33,10 +41,10 @@ int pci_bus_read_config_##size \
> unsigned long flags; \
> u32 data = 0; \
> if (PCI_##size##_BAD) return PCIBIOS_BAD_REGISTER_NUMBER; \
> - raw_spin_lock_irqsave(&pci_lock, flags); \
> + pci_lock_config(flags); \
> res = bus->ops->read(bus, devfn, pos, len, &data); \
> *value = (type)data; \
> - raw_spin_unlock_irqrestore(&pci_lock, flags); \
> + pci_unlock_config(flags); \
> return res; \
> }
>
> @@ -47,9 +55,9 @@ int pci_bus_write_config_##size \
> int res; \
> unsigned long flags; \
> if (PCI_##size##_BAD) return PCIBIOS_BAD_REGISTER_NUMBER; \
> - raw_spin_lock_irqsave(&pci_lock, flags); \
> + pci_lock_config(flags); \
> res = bus->ops->write(bus, devfn, pos, len, value); \
> - raw_spin_unlock_irqrestore(&pci_lock, flags); \
> + pci_unlock_config(flags); \
> return res; \
> }
>
>
>
