Commit 714fe383 authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

PCI: Provide Kconfig option for lockless config space accessors 



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.

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.

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarBjorn Helgaas <helgaas@kernel.org>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: linux-pci@vger.kernel.org
Link: http://lkml.kernel.org/r/20170316215057.205961140@linutronix.de


Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent bb290fda

drivers/pci/Kconfig

+3 −0
Original line number Diff line number Diff line
@@ -86,6 +86,9 @@ config PCI_ATS 
config PCI_ECAM

	bool



config PCI_LOCKLESS_CONFIG

	bool



config PCI_IOV

	bool "PCI IOV support"

	depends on PCI

drivers/pci/access.c

+12 −4
Original line number Diff line number Diff line
@@ -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;							\

}

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