cpu-cycles | 易学教程

(n - Multiplication) vs (n/2 - multiplication + 2 additions) which is better?

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问题 I have a C program that has n multiplications (single multiplication with n iterations) and I found another logic that has n/2 iterations of (1 multiplication + 2 additions). I know about the complexity that both are of O(n). but in terms of CPU cycles. which is faster ? 回答1: First of all follow Dietrich Epp's first advice - measuring is (at least for complex optimization problems) the only way to be sure. Now if you want to figure out why one is faster than the other, we can try. There are

Does a one cycle instruction take one cycle, even if RAM is slow?

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问题 I am using an embedded RISC processor. There is one basic thing I have a problem figuring out. The CPU manual clearly states that the instruction ld r1, [p1] (in C: r1 = *p1) takes one cycle. Size of register r1 is 32 bits. However, the memory bus is only 16 bits wide. So how can it fetch all data in one cycle? 回答1: The clock times are assuming full width zero wait state memory. The time it takes for the core to execute that instruction is one clock cycle. There was a time when each

How to set CPU load on a Red Hat Linux box?

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问题 I have a RHEL box that I need to put under a moderate and variable amount of CPU load (50%-75%). What is the best way to go about this? Is there a program that can do this that I am not aware of? I am happy to write some C code to make this happen, I just don't know what system calls will help. 回答1: This is exactly what you need: http://weather.ou.edu/~apw/projects/stress/ From the homepage: "stress is a simple workload generator for POSIX systems. It imposes a configurable amount of CPU,

Approximate Number of CPU Cycles for Various Operations

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I am trying to find a reference for approximately how many CPU cycles various operations require. I don't need exact numbers (as this is going to vary between CPUs) but I'd like something relatively credible that gives ballpark figures that I could cite in discussion with friends. As an example, we all know that floating point division takes more CPU cycles than say doing a bitshift. I'd guess that the difference is that the division is around 100 cycles, where as a shift is 1 but I'm looking for something to cite to back that up. Can anyone recommend such a resource? ant grobbelar I did a

How to set CPU load on a Red Hat Linux box?

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I have a RHEL box that I need to put under a moderate and variable amount of CPU load (50%-75%). What is the best way to go about this? Is there a program that can do this that I am not aware of? I am happy to write some C code to make this happen, I just don't know what system calls will help. This is exactly what you need: http://weather.ou.edu/~apw/projects/stress/ From the homepage: "stress is a simple workload generator for POSIX systems. It imposes a configurable amount of CPU, memory, I/O, and disk stress on the system. It is written in C, and is free software licensed under the GPL."

How many and what size cycles will be needed to perform longword transferred to the CPU

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问题 The task is for architecture ColdFire processor MCF5271: I don't understand how many and what size cycles will be needed to perform a longword transfer to the CPU, or word transfers. I'm reading the chart and I don't see what the connection is? Any comments are very appreciated. I've attached 2 examples with the answers. DATA BUS SIZE 回答1: The MCF5271 manual discusses the external interface of the processor in Chapter 17. The processor implements a byte-addressable address space with a 32-bit

How many and what size cycles will be needed to perform longword transferred to the CPU

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The task is for architecture ColdFire processor MCF5271: I don't understand how many and what size cycles will be needed to perform a longword transfer to the CPU, or word transfers. I'm reading the chart and I don't see what the connection is? Any comments are very appreciated. I've attached 2 examples with the answers. DATA BUS SIZE The MCF5271 manual discusses the external interface of the processor in Chapter 17. The processor implements a byte-addressable address space with a 32-bit external data bus. The D[31:0] signals represent the data bus, the A[23:0] signals represent the address

Is a mov to a segmentation register slower than a mov to a general purpose register?

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问题 Specifically is: mov %eax, %ds Slower than mov %eax, %ebx Or are they the same speed. I've researched online, but have been unable to find a definitive answer. I'm not sure if this is a silly question, but I think it's conceivable modifying a segmentation register could make the processor do extra work. N.B I'm concerned with old x86 linux cpus, not modern x86_64 cpus, where segmentation works differently. 回答1: mov %eax, %ebx between general-purpose registers is one of the most common

Is a mov to a segmentation register slower than a mov to a general purpose register?

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Specifically is: mov %eax, %ds Slower than mov %eax, %ebx Or are they the same speed. I've researched online, but have been unable to find a definitive answer. I'm not sure if this is a silly question, but I think it's conceivable modifying a segmentation register could make the processor do extra work. N.B I'm concerned with old x86 linux cpus, not modern x86_64 cpus, where segmentation works differently. mov %eax, %ebx between general-purpose registers is one of the most common instructions. Modern hardware supports it extremely efficiently, often with special cases that don't apply to any

How do I obtain CPU cycle count in Win32?

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In Win32, is there any way to get a unique cpu cycle count or something similar that would be uniform for multiple processes/languages/systems/etc. I'm creating some log files, but have to produce multiple logfiles because we're hosting the .NET runtime, and I'd like to avoid calling from one to the other to log. As such, I was thinking I'd just produce two files, combine them, and then sort them, to get a coherent timeline involving cross-world calls. However, GetTickCount does not increase for every call, so that's not reliable. Is there a better number, so that I get the calls in the right