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