How to measure memory bandwidth currently being used on Linux?

12
votes

I'm writing a small Linux application which logs the computer's power consumption along with CPU utilisation and disk utilisation. I'd like to add the ability to log memory bandwidth currently being used so I can see how well that correlates with a power consumption.

I understand that I can get information about the amount of memory currently allocated from /proc/meminfo but, of course, that doesn't tell me how much bandwidth is being used at present. Does anyone know how I could measure memory bandwidth currently in use?

edit I'd like this to work primarily on the x86 and x86-64 platforms

1
c++linuxmemory
What "memory bandwidth" ? That as such is a constant quantity of the system, but even so there's a difference between L1 / L2 / L3 cache bandwidth, memory bandwidth for memory attached to the local CPU, attached to a "remote" CPU (if using a HT / QPI system), memory bandwidth for e.g. memory residing on the graphics card. Things like cache hit rates, cache fill/spill, CPU pipeline stalls due to memory waits etc. are quite probably a better measure / a better indicator of things amiss than a "glossy single figure". - FrankH.
@Frank: All excellent questions. The short answer is: I'd love to measure and log all the metrics you mention L1 & L2 & L3 & main memory utilisation). My ultimate aim with this app is to be able to accurately predict power consumption without empirically measuring power consumption; instead I want to predict power consumption given only performance metrics like CPU utilisation, disk utilisation and memory utilisation. Perhaps I should've said "memory utilisation" instead of "memory bandwidth". - Jack Kelly
On those, indeed they're very CPU-dependent; On Solaris/SPARC, there are utilities like busstat, cputrack or trapstat to give you many of these figures, but those have never been ported to x86 (nor would they, due to hardware architecture dependency). For Linux, lwn.net/Articles/312720 gives a starting point for how to interact with the performance monitoring counters; the perf project wiki site is perf.wiki.kernel.org/index.php/Main_Page which also gives examples. - FrankH.

1 Answers

7
votes

It's highly CPU-dependent but you'll need to be able to get access to the CPU's performance registers. You may be able to do this via oprofile. Note that not all CPUs have a performance register (or combination of registers) which can be used to calculate to memory bandwidth usage, however.