maximumpc.com OCT 2019 MAXIMUMPC 15
Jarred Walton
TECH TALK
Jarred Walton
TECH TALK
Jarred Walton has been a
PC and gaming enthusiast
for over 30 years.Not All Cores Are Created
Equal in Zen 2 Processors
Most of the time, your CPU runs at some in-
between clock speed, usually closer to the boost
clock than the base clock. However, with AMD’s Zen
2 and third-gen Ryzen CPUs, things have changed.
I noticed this while testing, specifically in single-
threaded workloads like Cinebench 1T. With most
CPUs, such a test would show individual cores
hitting the specified boost clock, and one core
would always run at 100 percent utilization and the
maximum clock speed. In practice, depending on
the motherboard firmware and other factors, this
isn’t always the case, but with Ryzen 3000 CPUs,
no core hit—let alone sustained—the maximum
boost clock. For the Ryzen 9 3900X, Ryzen 7 3700X,
and Ryzen 5 3600X, the highest clock speed my
tools showed was 50–100MHz lower.
Others have noted similar behavior, and
eventually AMD disclosed more information. In
short, the cores in Zen 2 processors are not all
rated to hit equal performance levels; there are
usually one to three cores that are better than
most other cores, and some cores that are worse.
In practice, Windows 10 version 1809 (October 2018
update) and later support thread pinning, where
the OS schedules single-threaded tasks to the best
core. The potential problem is what happens with
the other cores—or other OSes.
AMD CPUs appear to have a 75–100MHz gap
between the best and worst cores in any given
SINCE THE INTRODUCTION of variable clock speeds
and boost/turbo clocks, most CPUs have behaved
in a similar fashion. The base clock is the minimum
guaranteed speed, and the boost is the maximum a
CPU can hit—but only in certain situations.
chip. It’s related to the binning and
chip yields I discussed last month,
only now the binning appears to be
related to maximum clock speed
and voltage for a single core, plus
minimum achievable clock speeds
of the other cores. With AMD’s
Precision Boost tech dynamically
altering CPU clock speed with a
granularity of 25MHz, the cores in
a Ryzen CPU run at their maximum
individual levels under heavy
workloads. However, the sustained
all-core clock speeds can and do
vary between individual chips.
This has implications for
overclocking—the maximum all-
core overclocks are generally
200–300MHz lower than the
maximum rated boost clock with
third-gen Ryzen (depending on
the model). Because overclocking
with Ryzen requires users to
set all cores to the same target
clock speed, performance is
often worse when you overclock.
Single-threaded workloads run
up to 300MHz slower, and even
multithreaded workloads may
average higher clock speeds
without overclocking. It seems
that winning the silicon lottery
might have more wide-ranging
implications than previously.
It’s also important to note that
AMD’s Zen 2 CPU core behavior
isn’t entirely new. Intel’s enthusiastprocessors, such as the Core i9-
9980XE, have two boost clocks:
Turbo Boost 2.0 is the maximum
clock speed that each core can
reach, while Turbo Boost Max 3.0 is
the maximum clock speed for the
two best cores. There have also
been mobile processors where one
or more cores could reach higher
clock speeds than the other cores.
The difficulty right now is that AMD
has no official public statement
as to the minimum clock speed of
each core with Ryzen 3000. It’s at
least the base clock, but it could be
higher—or it could vary by chip.
This sort of behavior will likely
become even more commonplace
as processor technology becomes
increasingly complex. AMD’s
change in boost policy may be in
par t due to the move to 7nm, and as
we move toward 5nm and smaller
in the future, it makes sense for
processor s to make the most of the
available resources.Sustained all-core clock speeds
can and do vary between
individual chips.
Third-gen Ryzens have different
boost clock behavior from
previous Ryzen processors.