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https://github.com/retspen/webvirtcloud
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The VM page's getters read the domain XML on their own: one load made 86 libvirt calls for a real VM, 29 of them for the same three XML documents (live, live with secrets, persistent) and 6 for the host capabilities. Each call is a round trip to the host. wvmInstance.cached_reads() is a block in which _XMLDesc (per flags value) and get_cap_xml are read from libvirt once; it ends with the block, even on an error, does not nest, and _defineXML drops it. Outside a block every read goes to libvirt as before. Only the VM page view, which does not change the VM, uses it, around its rendering. Views that change the VM keep reading fresh XML: most changes (devices, QoS, memory) do not go through _defineXML, and several views read, change and define more than once in one request. Measured on the test host: 86 -> 55 calls (XMLDesc 29 -> 3, getCapabilities 6 -> 1) for one VM, 82 -> 54 for another; the page took 0.23-0.25 s before, 0.14-0.15 s after. The HTML of both pages is identical before and after (CSRF tokens aside). A test renders the page on libvirt's test driver through the real getters: 25 XML reads before, one per kind now.
113 lines
3.3 KiB
Python
113 lines
3.3 KiB
Python
"""wvmInstance.cached_reads(): inside the block the domain XML (per flags) and
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the host capabilities are read from libvirt once; outside it every read goes
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to libvirt, as code that changes the VM needs."""
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import unittest
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from django.conf import settings
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if not settings.configured:
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settings.configure(MAC_OUI="52:54:10")
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from vrtManager.instance import wvmInstance
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class FakeDomain:
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def __init__(self):
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self.reads = []
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self.fail = False
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def XMLDesc(self, flags):
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if self.fail:
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raise RuntimeError("libvirt error")
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self.reads.append(flags)
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return f"<domain flags='{flags}' read='{len(self.reads)}'/>"
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class FakeConn:
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def __init__(self):
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self.caps = 0
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self.defined = []
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def getCapabilities(self):
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self.caps += 1
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return "<capabilities/>"
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def defineXML(self, xml):
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self.defined.append(xml)
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def proxy():
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p = wvmInstance.__new__(wvmInstance) # no connection: only these calls
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p.instance = FakeDomain()
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p.wvm = FakeConn()
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return p
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class CachedReadsTestCase(unittest.TestCase):
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def test_outside_the_block_every_read_goes_to_libvirt(self):
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p = proxy()
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p._XMLDesc(0)
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p._XMLDesc(0)
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p.get_cap_xml()
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p.get_cap_xml()
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self.assertEqual((p.instance.reads, p.wvm.caps), ([0, 0], 2))
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def test_inside_the_block_each_flags_value_is_read_once(self):
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p = proxy()
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with p.cached_reads():
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first = [p._XMLDesc(0), p._XMLDesc(1), p._XMLDesc(3)]
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again = [p._XMLDesc(0), p._XMLDesc(1), p._XMLDesc(3)]
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p.get_cap_xml()
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p.get_cap_xml()
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self.assertEqual(first, again)
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self.assertEqual(p.instance.reads, [0, 1, 3])
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self.assertEqual(p.wvm.caps, 1)
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def test_the_block_ends_with_its_cache(self):
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p = proxy()
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with p.cached_reads():
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p._XMLDesc(0)
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with p.cached_reads():
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p._XMLDesc(0)
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p._XMLDesc(0)
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self.assertEqual(p.instance.reads, [0, 0, 0])
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def test_an_error_inside_the_block_still_ends_it(self):
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p = proxy()
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with self.assertRaises(ValueError), p.cached_reads():
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p._XMLDesc(0)
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raise ValueError
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p._XMLDesc(0)
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self.assertEqual(p.instance.reads, [0, 0])
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def test_a_failed_read_is_not_cached(self):
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p = proxy()
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with p.cached_reads():
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p.instance.fail = True
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with self.assertRaises(RuntimeError):
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p._XMLDesc(0)
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p.instance.fail = False
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p._XMLDesc(0)
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self.assertEqual(p.instance.reads, [0])
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def test_a_definition_change_drops_the_cache(self):
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p = proxy()
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with p.cached_reads():
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p._XMLDesc(3)
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p._defineXML("<domain/>")
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p._XMLDesc(3)
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self.assertEqual(p.instance.reads, [3, 3])
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def test_blocks_do_not_nest(self):
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p = proxy()
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with p.cached_reads(), self.assertRaises(RuntimeError), p.cached_reads():
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pass
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def test_two_proxies_do_not_share_a_cache(self):
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a, b = proxy(), proxy()
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with a.cached_reads():
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a._XMLDesc(0)
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b._XMLDesc(0)
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b._XMLDesc(0)
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self.assertEqual((a.instance.reads, b.instance.reads), ([0], [0, 0]))
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