INTERRUPT AFFINITY POLICY GUIDE

1.

HOW TO SET
AFFINITIES
By Alchemy Tweaks

2.

Understanding the Interrupt Affinity Policy Tool
Demystifying the Interrupt Affinity Policy Tool
The 'Interrupt Affinity Policy Tool,' a Microsoft creation, empowers users to designate specific CPUs (threads) for device
management. This guide details how to proficiently select suitable CPUs (threads) for your GPU and USB devices.
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3.

Reliable Tool, Expert Handling Required
Rest assured, this tool boasts a track record of safety across numerous computer systems.
However, challenges may arise if used without a comprehensive understanding. Potential issues
include:
1. Latency issues
2. FPS Drops
3. Freezes
4. Stutters
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4.

How to set GPU & USB affinities?
First of all, you have to check if you have (ΗΤ) hyper threading & (SMT) Simultaneous
Multithreading ON or OFF.
I suggest to disable HT or SMT if you have at least 12 threads. Otherwise enable it.
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5.

Key Distinction: HT/SMT Enabled Configuration
A pivotal divergence lies in HT (Hyper-Threading) or SMT (Simultaneous Multithreading) setups,
necessitating the selection of 2 CPUs. For instance, consider the X system where optimal CPUs
(threads) are CPU 0 and CPU 1. CPU 0 denotes the primary thread, while CPU 1 signifies the
hyper-thread. Notably, the hyper-thread yields half the processing prowess of the thread.
Consequently, this dual CPU selection addresses the nuanced performance dynamics.
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6.

What difference does it make to the process if I have
HT or SMT enabled or disabled? (part 2)
If we have disabled HT or SMT then we will simply choose 1 CPU (thread).
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7.

How to set GPU affinities?
I'd like to clarify that the procedure remains consistent irrespective of HT/SMT activation status.
The steps remain unchanged; simply adhere to the guidelines outlined in the preceding slides.
The tools we will need are as follows:
1. Interrupt affinity policy tool
2. Latency Monitor
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Open Windows Device manager > view > device by connection > search for your GPU > properties > check location .
Run as administrator interrupt affinity policy tool and search for your GPU and set the affinity [ [CPU(thread) or CPUs (thread & hyper-thread
for HT/SMT ON)]
Do the same thing for the “PCI Express Root Port”
Run latency monitor go to drivers tab and search for the nvidia driver.
Check Highest execution and Total execution , the affinity with the lowest numbers is the best.
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9.

How to set GPU affinities? (Second way)
The tools we will need are as follows:
1. Interrupt affinity policy tool
2. Auto GPU Affinity
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10.

How it works Auto GPU Affinity?
Execute 'Auto Gpu Affinity' via the command-line, and hit 'Enter' to initiate the benchmarking
process.
Once the tool completes core benchmarking, GPU affinity will revert to the Windows default,
and a results table will emerge. The xperf report resides in the designated session directory.
Conduct a minimum of 3 tool runs. Should a single core consistently exhibit strong
performance and the 0.005% Lows values align well with other outcomes, your results
achieve reproducibility, confirming the consistency of your testing environment.
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11.

After all the tests we did are completed, we head out to this path: “Auto Gpu Affinity\captures”.
In each test we look at the 1% low & 0.1% low
If out of the 5 tests, 3 come out as the best CPU, for example CPU 1 is the best according 1% low and CPU 2
according 0.1% low and Max FPS .
Note! During the tests, the computer is not used and you have made sure that no unnecessary processes are
running. In the case that you cannot get a result with 3 tests, continue to do the above benchmarks or try the previous
method.
Don't forget to put the affinity on the “PCI Express Root Port” beyond the GPU.
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Are there possible bugs?
At each end of the test the table will theoretically appear, however in several cases the table
does not appear and you must manually find the results by following this
path:“AutoGpuAffinity\captures”
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13.

How to set affinities for all USB devices?(1)
In my opinion, what you should focus on is, the distance between the highest and the lowest frequency should be
as small as possible, with this reasoning you will find the best affinity.
There is no official way to find the best affinity for our USB devices. I think the primary goal is to stabilize the DPI
of the mouse, keyboard or controller. For example, it should be as stable as possible at 1000 polling rate.
However there are 2 obvious ways to find the best affinities. The first is with the Latency monitor to check if there
are decreases or increases in latency after applying the changes. The second obvious and quite difficult way is to
observe with our own eyes the experience we have in games, if for example it is smoother, with less delay, etc.
The way I will show which is the most commonly accepted is by using the mouse tester. So this program helped
us to see in a graph the frequency of our mouse.
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14.

How to set affinities for Only 1 device?(2)
Furthermore, certain tweakers suggest exploring both singular and collective device affinities. Their rationale is straightforward: associating
more devices within a single affinity can contribute to increased latency. While I cannot definitively verify its efficacy, experimentation is
encouraged. Illustrated in the image is my personal example, showcasing an assigned affinity for my mouse device.
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Α possible result when you put specific affinity for a
specific device
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ABOUT GRAPHS OF MOUSE TESTER
Securing these graphs presents a considerable challenge, heavily
influenced by the Windows 10 version. Particularly in version 1709,
despite the need for meticulous system refinement, achieving a
remarkably stable graph was feasible. Contrastingly, the more recent
Windows iterations (21H2, 22H2) struggle to yield a stable graph,
making attainment nearly improbable.
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About CPI!
Set the CPI (Counts Per Inch) that you using . To check the CPI use the manual of your
mouse or the software.
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18.

About Data point
This essentially fine-tunes the post-test appearance of the graph. The numerical values you input
are contingent on the graph's outcomes and the pace at which you executed mouse movements.
Prevailing combinations include:
200 - 500
200 - 1000
500 - 1000
1000 - 2000
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19.

How to use mouse tester?
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Close all unnecessary background processes
Set the affinity after you have checked the device location of USB devices (Generic USB xHCI Host Controller)
Open mouse tester
Set 800 CPI, then click LOG START (F2) and start spinning fast circles for 5-6 seconds, then click LOG START (F2) again
and click PLOT now in new window click FREQUENCY VS TIME
Check the graph and the affinity with the most stable graph is the best (check the photos on the next tabs to see the right
graph) , you must repeat the process 2-3 times for each affinity to be sure about the results.
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20.

Are there possible bugs?
Prior to anything else, it's vital to emphasize that during the test, swift mouse movements,
creating circular patterns, are of utmost importance.
Moreover, when altering affinities for USB devices, a scenario might arise wherein, after 3-4
tests involving distinct CPUs, the peripherals cease functioning. Should this occur, refrain
from panic. Instead, perform a computer restart and verify the applied affinity settings.
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An example with mouse tester
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ENDING
It's crucial to acknowledge that every system, graphics card, keyboard, and other components are
inherently unique, thus yielding distinct results for each individual. The pivotal factor is to cultivate
patience and a systematic approach. The cornerstone of success lies in comprehending the
intricacies of the software you employ.
For recommendations or error identification, feel free to contact me via Discord.
Discord Name: Alchemy Tweaks#3412
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