What is IPC

[ashu1106]

I know what IPC stands for but I want to know that how it effects a cpu's performance in games and in other pro applications. And how to measure IPC of a CPU. 

Thanks.

[Sauron]

You can't reliably measure the IPC of modern CPUs without very specific instruments, but you can make a relative estimate based on single core performance and clock speed. Just divide the first by the second.

 

As for how it affects programs, it depends on the program. In general, given the same clock speed and core count, a higher IPC cpu will be faster.

[Damascus]

To measure ipc on a cpu you do a clock for clock/core for core test.  Whatever does better has better ipc if the application isn't poorly optimized for one cpu or the other.

[Mira Yurizaki]

It stands for instructions per clock. Which is how much stuff can the CPU do on a given clock cycle.

 

There's no way to directly measure IPC. You can run some programs that'll test one aspect of a CPU to get an idea, but that won't be the actual value. The only way you can really measure it is indirectly by testing the CPU with a variety of benchmarks, then compare that to another CPU that also ran those same benchmarks.

[Sniperfox47]

Just now, ashu1106 said:

I know what IPC stands for but I want to know that how it effects a cpu's performance in games and in other pro applications. And how to measure IPC of a CPU. 

Thanks.

IPC or instructions per clock, is a measurement of how many CPU instructions a CPU can do, on average, per clock cycle. The IPC of a processor is the small non-clock boosts to performance and for example a 20% boost in IPC would yield the same relative benefits as a 20% boost in clock speeds.

 

To measure it, you'd fix clock rate on your CPU so it doesn't change, create an application that does a number of basic computations, measure the time between these computations and use that to determine how many of these basic computations happened, on average, per clock cycle.

 

This number isn't particularly useful however since a processors IPC will vary by instruction, by code complexity, and by a large number of other factors. The best you can talk about is the relative IPC for a given workload.

[minibois]

IPC = instruction per clock.

How much stuff a CPU can do per (G)Hz.

 

This unfortunately cannot easily be calculated, since it depends on how well the given program works with a CPU, so one program will give other IPC rating than others.

[ashu1106]

So if it is relative, tech reviewers always comment on a cpu's IPC in relative terms. Right?

Because I remember when ryzen was first launched almost every review praised it for it's higher IPC, but none of them told how much higher it is. 

Another thing, is IPC defined for per core or for CPU as a whole 

[DocSwag]

IPC is a complicated topic. You can't pinpoint it as a specific number, because it varies. 

 

CPUs have many different units inside them to handle different workloads. For example, every modern CPU has ALUs and FPUs (for doing integer and floating point instructions). Some CPUs may have stronger ALUs, but weaker FPUs. Which would make their integer IPC very good, but their floating point IPC very bad.

 

As well, weird latency characteristic, such as those caused by the infinity fabric on Ryzen, could heavily affect performance in some scenarios that require low latency cross core communications, whereas other scenarios might not care at all.

 

For measuring IPC, usually people just take a ton of benchmarks and then find an average to determine IPC. There's not really a better way of doing it. And even if you do know the approximate IPC of a CPU, that can only give you a rough estimate of how it would perform in a given scenario since it varies. The best way, as always, is to check benchmarks.

2 minutes ago, ashu1106 said:

So if it is relative, tech reviewers always comment on a cpu's IPC in relative terms. Right?

Because I remember when ryzen was first launched almost every review praised it for it's higher IPC, but none of them told how much higher it is. 

Another thing, is IPC defined for per core or for CPU as a whole 

IPC can be measured as an absolute number. Of course, this number wouldn't re representative of all scenarios but it would be the approximate IPC of a cpu. Like for example, you could have a CPU with an IPC of 2 instructions per clock.

 

IPC can be defined for a whole cpu, but generally people only use it for measuring per core performance since then you could say a ryzen 8 core has higher ipc than a ryzen 4 core and then comparisons and stuff get super complicated.

[Damascus]

Ryzen has 40% better ipc than ads last cpus, the bulldozer and Co.  Architectures

[DocSwag]

3 minutes ago, Damascus said:

Ryzen has 40% better ipc than ads last cpus, the bulldozer and Co.  Architectures

52% actually, according to specINT

[X_X]

How to measure IPC and values for different processors can be found here but likely not exactly what you are looking for.