trunk/lttv/doc/developer/xen-port.txt

   1
   2
   3 Xen port notes
   4
   5 Mathieu Desnoyers, April 2006
   6
   7 Useful files :
   8
   9 common/trace.c
  10 include/xen/trace.h and the dom0 op in include/public/dom0_ops.h
  11
  12 alloc buffer (alloc_trace_bufs) :
  13 alloc_xenheap_pages
  14
  15 Shared buffer between dom0 and hypervisor :
  16 share_xen_page_with_privileged_guests
  17
  18
  19
  20 trace_create / trace_destroy :
  21
  22 call xen hooks from dom0 to allocate a new buffer, get the newly allocated
  23 struct trace pointer.
  24 Share struct traces with dom0 to have offset and consumed counts.
  25 Share the buffers with dom0 too.
  26
  27 Create a new "xen" channel.
  28
  29
  30 Create 4 new xen facilities (see include/public/trace.h) :
  31 xen_sched  (grep TRC_SCHED)
  32   sched_dom_add
  33         sched_dom_rem
  34         sched_sleep
  35         sched_wake
  36         sched_yield
  37         sched_block
  38         sched_shutdown
  39         sched_ctl
  40         sched_switch
  41         sched_s_timer_fn
  42         sched_t_timer_fn
  43         sched_dom_timer_fn
  44         sched_dom_timer_fn
  45         sched_switch_infprev
  46         sched_switch_infnext
  47 xen_dom0op (grep TRC_DOM0OP)
  48   dom0op_enter_base
  49   dom0op_leave_base
  50 xen_vmx (grep TRC_VMX)
  51   vmx_vmexit
  52   vmx_vmentry
  53         vmx_timer_intr
  54         vmx_int
  55         vmx_io
  56 xen_mem (grep TRC_MEM)
  57   mem_page_grant_map
  58         mem_page_grant_unmap
  59         mem_page_grant_transfer
  60
  61
  62 How to share xen pages efficiently ?
  63 Pages allocated in xen heap, the shared with dom0.
  64
  65 How buffers are accessed in dom0 ?
  66 directly from pointers to buffers contained in get_info control information.
  67
  68 do_dom0_op
  69
  70 tbufcontrol -> control info
  71   int tb_control(dom0_tbufcontrol_t *tbc)
  72
  73 DOM0_TBUF_GET_INFO  buffer_mfn   __pa(t_bufs[0]) >> PAGE_SHIFT;
  74
  75
  76 create trace :
  77
  78 in :
  79 trace name
  80 buffer size
  81 return : 0 success, 1 failure
  82 do :
  83 alloc buffer xen
  84 share with dom0
  85
  86 destroy trace :
  87 in :
  88 trace name
  89 do : unshare buffer / free.
  90
  91
  92 start/stop :
  93 tb_control that will update the control structure.
  94 in : trace name
  95 start : put active to 1 + inc. nb_active traces
  96 stop : put active to 0 + dec nb_active traces.
  97 return : 0 success, 1 failure.
  98
  99 consume :
 100 in : trace name
 101 tb_control that will update the consumed count.
 102 in : old count.
 103 return : 0 success, 1 failure (pushed).
 104
 105 get_info :
 106 tb_control that returns a fresh copy of trace control info.
 107
 108
 109
 110 NOTE 8-11-2006
 111
 112 Xen 3.0.3
 113 Only one init of buffers (cannot change buffer size)
 114 tbc->buffer_mfn = opt_tbuf_size ? virt_to_mfn(per_cpu(t_bufs, 0)) : 0;
 115 /* Convert between Xen-heap virtual addresses and machine frame numbers. */
 116 #define virt_to_mfn(va)     (virt_to_maddr(va) >> PAGE_SHIFT)
 117
 118 struct t_buf *tbufs_mapped;
 119
 120     tbufs_mapped = xc_map_foreign_range(xc_handle, DOMID_XEN,
 121                                         size * num, PROT_READ | PROT_WRITE,
 122                                         tbufs_mfn);
 123
 124 int fd = open("/proc/xen/privcmd", O_RDWR);
 125
 126 /* sleep for this long (milliseconds) between checking the trace buffers */
 127 #define POLL_SLEEP_MILLIS 100
 128
 129
 130 netfront.c
 131 xenbus_alloc_evtchn
 132 bind_evtchn_to_irqhandler
 133
 134
 135 virq :
 136
 137 include/public/xen.h VIRQ_TBUF
 138                         /* G. (DOM0) Trace buffer has records available. */
 139
 140 trace_notify_guest : send_guest_global_virq(dom0, VIRQ_TBUF);
 141
 142 see arch/i386/oprofile/xenoprof.c
 143 bind_virq
 144
 145
 146