<s>
The	O
Intel	B-Architecture
Ultra	I-Architecture
Path	I-Architecture
Interconnect	I-Architecture
(	O
UPI	O
)	O
is	O
a	O
point-to-point	O
processor	B-Architecture
interconnect	B-Protocol
developed	O
by	O
Intel	O
which	O
replaced	O
the	O
Intel	B-Architecture
QuickPath	I-Architecture
Interconnect	I-Architecture
(	O
QPI	B-Architecture
)	O
in	O
Xeon	B-Device
Skylake-SP	O
platforms	O
starting	O
in	O
2017	O
.	O
</s>
<s>
UPI	O
is	O
a	O
low-latency	O
coherent	B-Operating_System
interconnect	B-Protocol
for	O
scalable	O
multiprocessor	B-Operating_System
systems	O
with	O
a	O
shared	O
address	B-General_Concept
space	I-General_Concept
.	O
</s>
<s>
It	O
uses	O
a	O
directory-based	O
home	O
snoop	B-General_Concept
coherency	O
protocol	O
with	O
a	O
transfer	O
speed	O
of	O
up	O
to	O
10.4GT/s	O
.	O
</s>
<s>
Comparing	O
to	O
QPI	B-Architecture
,	O
it	O
improves	O
power	O
efficiency	O
with	O
a	O
new	O
low-power	O
state	O
,	O
improves	O
transfer	O
efficiency	O
with	O
a	O
new	O
packetization	O
format	O
,	O
and	O
improves	O
scalability	O
with	O
protocol	O
layer	O
that	O
does	O
not	O
require	O
preallocation	O
of	O
resources	O
.	O
</s>
<s>
UPI	O
only	O
supports	O
directory-based	O
coherency	O
,	O
unlike	O
previous	O
QPI	B-Architecture
processors	O
which	O
supported	O
multiple	O
snoop	B-General_Concept
modes	O
(	O
no	O
snoop	B-General_Concept
,	O
early	O
snoop	B-General_Concept
,	O
home	O
snoop	B-General_Concept
,	O
and	O
directory	O
)	O
.	O
</s>
<s>
A	O
combined	O
caching	O
and	O
home	O
agent	O
(	O
CHA	O
)	O
handles	O
resolution	O
of	O
coherency	O
across	O
multiple	O
processors	O
,	O
as	O
well	O
as	O
snoop	B-General_Concept
requests	O
from	O
processor	B-Architecture
cores	O
and	O
local	O
and	O
remote	O
agents	O
.	O
</s>
<s>
Separate	O
physical	O
CHAs	O
are	O
placed	O
within	O
each	O
processor	B-Architecture
core	O
and	O
last	O
level	O
cache	O
(	O
LLC	O
)	O
bank	O
to	O
improve	O
scalability	O
according	O
to	O
the	O
number	O
of	O
cores	O
,	O
memory	O
controllers	O
,	O
or	O
the	O
sub-NUMA	O
clustering	O
mode	O
.	O
</s>
<s>
The	O
address	B-General_Concept
space	I-General_Concept
is	O
interleaved	O
across	O
different	O
CHAs	O
,	O
which	O
act	O
like	O
a	O
single	O
logical	O
agent	O
.	O
</s>
