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https://github.com/torvalds/linux
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6dbde35308
It is an optimization and a cleanup, and adds the following new
generic percpu methods:
percpu_read()
percpu_write()
percpu_add()
percpu_sub()
percpu_and()
percpu_or()
percpu_xor()
and implements support for them on x86. (other architectures will fall
back to a default implementation)
The advantage is that for example to read a local percpu variable,
instead of this sequence:
return __get_cpu_var(var);
ffffffff8102ca2b: 48 8b 14 fd 80 09 74 mov -0x7e8bf680(,%rdi,8),%rdx
ffffffff8102ca32: 81
ffffffff8102ca33: 48 c7 c0 d8 59 00 00 mov $0x59d8,%rax
ffffffff8102ca3a: 48 8b 04 10 mov (%rax,%rdx,1),%rax
We can get a single instruction by using the optimized variants:
return percpu_read(var);
ffffffff8102ca3f: 65 48 8b 05 91 8f fd mov %gs:0x7efd8f91(%rip),%rax
I also cleaned up the x86-specific APIs and made the x86 code use
these new generic percpu primitives.
tj: * fixed generic percpu_sub() definition as Roel Kluin pointed out
* added percpu_and() for completeness's sake
* made generic percpu ops atomic against preemption
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Tejun Heo <tj@kernel.org>
61 lines
1.6 KiB
C
61 lines
1.6 KiB
C
#ifndef _XEN_MULTICALLS_H
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#define _XEN_MULTICALLS_H
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#include "xen-ops.h"
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/* Multicalls */
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struct multicall_space
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{
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struct multicall_entry *mc;
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void *args;
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};
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/* Allocate room for a multicall and its args */
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struct multicall_space __xen_mc_entry(size_t args);
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DECLARE_PER_CPU(unsigned long, xen_mc_irq_flags);
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/* Call to start a batch of multiple __xen_mc_entry()s. Must be
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paired with xen_mc_issue() */
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static inline void xen_mc_batch(void)
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{
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/* need to disable interrupts until this entry is complete */
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local_irq_save(__get_cpu_var(xen_mc_irq_flags));
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}
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static inline struct multicall_space xen_mc_entry(size_t args)
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{
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xen_mc_batch();
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return __xen_mc_entry(args);
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}
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/* Flush all pending multicalls */
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void xen_mc_flush(void);
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/* Issue a multicall if we're not in a lazy mode */
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static inline void xen_mc_issue(unsigned mode)
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{
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if ((paravirt_get_lazy_mode() & mode) == 0)
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xen_mc_flush();
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/* restore flags saved in xen_mc_batch */
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local_irq_restore(percpu_read(xen_mc_irq_flags));
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}
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/* Set up a callback to be called when the current batch is flushed */
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void xen_mc_callback(void (*fn)(void *), void *data);
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/*
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* Try to extend the arguments of the previous multicall command. The
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* previous command's op must match. If it does, then it attempts to
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* extend the argument space allocated to the multicall entry by
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* arg_size bytes.
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*
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* The returned multicall_space will return with mc pointing to the
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* command on success, or NULL on failure, and args pointing to the
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* newly allocated space.
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*/
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struct multicall_space xen_mc_extend_args(unsigned long op, size_t arg_size);
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#endif /* _XEN_MULTICALLS_H */
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