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Diffstat (limited to 'arch/x86/xen/multicalls.c')
-rw-r--r-- | arch/x86/xen/multicalls.c | 90 |
1 files changed, 90 insertions, 0 deletions
diff --git a/arch/x86/xen/multicalls.c b/arch/x86/xen/multicalls.c new file mode 100644 index 000000000000..c837e8e463db --- /dev/null +++ b/arch/x86/xen/multicalls.c @@ -0,0 +1,90 @@ +/* + * Xen hypercall batching. + * + * Xen allows multiple hypercalls to be issued at once, using the + * multicall interface. This allows the cost of trapping into the + * hypervisor to be amortized over several calls. + * + * This file implements a simple interface for multicalls. There's a + * per-cpu buffer of outstanding multicalls. When you want to queue a + * multicall for issuing, you can allocate a multicall slot for the + * call and its arguments, along with storage for space which is + * pointed to by the arguments (for passing pointers to structures, + * etc). When the multicall is actually issued, all the space for the + * commands and allocated memory is freed for reuse. + * + * Multicalls are flushed whenever any of the buffers get full, or + * when explicitly requested. There's no way to get per-multicall + * return results back. It will BUG if any of the multicalls fail. + * + * Jeremy Fitzhardinge <jeremy@xensource.com>, XenSource Inc, 2007 + */ +#include <linux/percpu.h> +#include <linux/hardirq.h> + +#include <asm/xen/hypercall.h> + +#include "multicalls.h" + +#define MC_BATCH 32 +#define MC_ARGS (MC_BATCH * 16 / sizeof(u64)) + +struct mc_buffer { + struct multicall_entry entries[MC_BATCH]; + u64 args[MC_ARGS]; + unsigned mcidx, argidx; +}; + +static DEFINE_PER_CPU(struct mc_buffer, mc_buffer); +DEFINE_PER_CPU(unsigned long, xen_mc_irq_flags); + +void xen_mc_flush(void) +{ + struct mc_buffer *b = &__get_cpu_var(mc_buffer); + int ret = 0; + unsigned long flags; + + BUG_ON(preemptible()); + + /* Disable interrupts in case someone comes in and queues + something in the middle */ + local_irq_save(flags); + + if (b->mcidx) { + int i; + + if (HYPERVISOR_multicall(b->entries, b->mcidx) != 0) + BUG(); + for (i = 0; i < b->mcidx; i++) + if (b->entries[i].result < 0) + ret++; + b->mcidx = 0; + b->argidx = 0; + } else + BUG_ON(b->argidx != 0); + + local_irq_restore(flags); + + BUG_ON(ret); +} + +struct multicall_space __xen_mc_entry(size_t args) +{ + struct mc_buffer *b = &__get_cpu_var(mc_buffer); + struct multicall_space ret; + unsigned argspace = (args + sizeof(u64) - 1) / sizeof(u64); + + BUG_ON(preemptible()); + BUG_ON(argspace > MC_ARGS); + + if (b->mcidx == MC_BATCH || + (b->argidx + argspace) > MC_ARGS) + xen_mc_flush(); + + ret.mc = &b->entries[b->mcidx]; + b->mcidx++; + ret.args = &b->args[b->argidx]; + b->argidx += argspace; + + return ret; +} |