tools/xend: Fix performance of xend with more than 10000 FC device paths

On server startup xend start or a later xend restart needs approx. 30 min to
start/restart. Without attached FC devices xend start/restart needs only some
seconds.

server type: Fujitsu Primergy RX600-S5

The time gets lost in xen/xend/XendNode.py line 329 while calling
vscsi_util.get_all_scsi_device().

329         for pscsi_record in vscsi_util.get_all_scsi_devices():
330             scsi_id = pscsi_record['scsi_id']
331             if scsi_id:
332                 saved_HBA_uuid = None

I think, in most cases we don't need all the PSCSI devices registered in
xend, but only a few of it.
So a good solution for this perforamce issue is to scan only the SCSI device
paths we need, controlled by a new option in xend-config.sxp.

I have made a patch to allow specification of scsi devices we need in xend
in the config file xend-config.sxp.
The new options pscsi-device-mask expects a list of device ids oder partial
device ids like the option of lsscsi, e.g.
(pscsi-device-mask ('<partial-dev-id1' 'partial-dev-id2' ...))

Without this option set in xend-config.sxp or if lsscsi is not support, all
device paths are process like today.

Signed-off-by: Lutz Dube Lutz.Dube@ts.fujitsu.com
Comment from Masaki Kanno <kanno.masaki@jp.fujitsu.com>: "Well done"
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>

tools/examples/xend-config.sxp

@@ -294,3 +294,11 @@
 # we have to realize this may incur security issue and we can't make sure the
 # device assignment could really work properly even after we do this.
 #(pci-passthrough-strict-check yes)
+
+# If we have a very big scsi device configuration, start of xend is slow,
+# because xend scans all the device paths to build its internal PSCSI device
+# list.  If we need only a few devices for assigning to a guest, we can reduce
+# the scan to this device. Set list list of device paths in same syntax like in
+# command lsscsi, e.g. ('16:0:0:0' '15:0') 
+# (pscsi-device-mask ('*'))
+

tools/python/xen/util/vscsi_util.py

@@ -148,11 +148,12 @@ def _vscsi_get_scsidevices_by_sysfs():
     return devices
 
 
-def vscsi_get_scsidevices():
+def vscsi_get_scsidevices(mask=""):
     """ get all scsi devices information """
 
-    devices = _vscsi_get_scsidevices_by_lsscsi("")
-    if devices:
+    devices = _vscsi_get_scsidevices_by_lsscsi("[%s]" % mask)
+    if devices or (len(mask) and mask[0] != "*"):
+        # devices found or partial device scan
         return devices
     return _vscsi_get_scsidevices_by_sysfs()
 
@@ -274,9 +275,9 @@ def get_scsi_device(pHCTL):
             return _make_scsi_record(scsi_info)
     return None
 
-def get_all_scsi_devices():
+def get_all_scsi_devices(mask=""):
     scsi_records = []
-    for scsi_info in vscsi_get_scsidevices():
+    for scsi_info in vscsi_get_scsidevices(mask):
         scsi_record = _make_scsi_record(scsi_info)
         scsi_records.append(scsi_record)
     return scsi_records

tools/python/xen/xend/XendNode.py

@@ -326,7 +326,12 @@ class XendNode:
         pscsi_table = {}
         pscsi_HBA_table = {}
 
-        for pscsi_record in vscsi_util.get_all_scsi_devices():
+        pscsi_records = []
+        for pscsi_mask in xendoptions().get_pscsi_device_mask():
+            pscsi_records += vscsi_util.get_all_scsi_devices(pscsi_mask)
+        log.debug("pscsi record count: %s" % len(pscsi_records))
+
+        for pscsi_record in pscsi_records:
             scsi_id = pscsi_record['scsi_id']
             if scsi_id:
                 saved_HBA_uuid = None

tools/python/xen/xend/XendOptions.py

@@ -164,6 +164,9 @@ class XendOptions:
         """
         print >>sys.stderr, "xend [ERROR]", fmt % args
 
+    """Default mask for pscsi device scan."""
+    xend_pscsi_device_mask = ['*']
+
 
     def configure(self):
         self.set_config()
@@ -430,6 +433,10 @@ class XendOptions:
         return self.get_config_bool("pci-passthrough-strict-check",
                                     self.pci_dev_assign_strict_check_default)
 
+    def get_pscsi_device_mask(self):
+        return self.get_config_value("pscsi-device-mask",
+                                      self.xend_pscsi_device_mask)
+
 class XendOptionsFile(XendOptions):
 
     """Default path to the config file."""