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SubjectRe: Why /proc/cpuinfo doesn't print L1,L2,L3 caches?
J.C. Pizarro wrote:
> On 2008/3/25, Chris Snook <csnook@redhat.com> wrote:
>> J.C. Pizarro wrote:
>> > $ cat /proc/cpuinfo
>> > processor : 0
>> > vendor_id : AuthenticAMD
>> > cpu family : 15
>> > model : 47
>> > model name : AMD Athlon(tm) 64 Processor 3200+
>> > ...
>> > cache size : 512 KB
>> > ...
>> >
>> > The cache size is currently misinformed. It's not the real size because
>> > it's 64+64+512 KiB = 640 KiB, not 512 KB.
>> >
>> > How can i know what hw-caches use the processors?
>> > The current kernel doesn't know well what hw-caches uses.
>> >
>> > The good proposal is by example (the data below are not real):
>> > * In old AMD Athlon64:
>> >
>> > cache L1 : 64 KiB I + 64 KiB D, 64 B line, direct way, ...
>> > cache L2 : 512 KiB I+D-shared, exclusive, 128 associative way, ...
>> > cache L3 : none
>> >
>> > * In Intel Core Duo:
>> > processor : 0
>> > cache L1 : 32 KiB I + 32 KiB D, 64 B line, direct way, ...
>> > cache L2 : 2048 KiB Cores-shared, inclusive, 128 associative way, ...
>> > cache L3 : none
>> >
>> > processor : 1
>> > cache L1 : 32 KiB I + 32 KiB D, 64 B line, direct way, ...
>> > cache L2 : 2048 KiB cores-shared, inclusive, 128 associative way, ...
>> > cache L3 : none
>> >
>> > * In Quad:
>> > processor : 0
>> > cache L1 : 32 KiB I + 32 KiB D, 64 B line, direct way, ...
>> > cache L2 : 2048+2048 KiB pair-cores-shared, inclusive, 128
>> > associative way, ...
>> > cache L3 : none
>> > ...
>> > processor : 3
>> > cache L1 : 32 KiB I + 32 KiB D, 64 B line, direct way, ...
>> > cache L2 : 2048+2048 KiB pair-cores-shared, inclusive, 128
>> > associative way, ...
>> > cache L3 : none
>> >
>> > It above is an example, put your symbols to /proc/cpuinfo in a
>> > convenient manner.
>> >
>> > Good bye ;)
>>
>>
>> I think you want this:
>>
>> /sys/devices/system/cpu/cpu0/cache
>
> Thanks, but there is not easier manner to print the properties of hw-caches
> unless printing recursively this tree /sys/devices/system/cpu/cpu[0-9]+/cache/
> that they are only numbers without symbolic fields.

Then use dmidecode. It's all in one place, and everyone expects it to be far
too long to read at a glance.

> There is not manner to know the speed (in MHz) of the L1, L2 and L3 caches.
>
>> /proc/cpuinfo is intended to give a general summary of certain properties of the
>> processor that tend to be particularly interesting, and present them all in one
>> place. It is not intended to expose everything the kernel knows about every
>> processor on the system.
>
> /proc/cpuinfo doesn't give a general summary because it gives superfluous info.
>
> I think that it's better to refactorize /proc/cpuinfo still more.
>
> (
> ... fields common to all present processors known by the kernel ....
> [ to warn if the values are differents between cores ]
> )
> (
> ... specific fields for each processor ... by example:
>
> processor : 0
> cpu MHz : 2000.000 # normal clocked
> bogomips : 4010.63
> processor : 1
> cpu MHz : 500.000 # underclocked for energy saving ...
> bogomips : 1003.20
>
> )
>
> I think that all the cores are equals in almost non-weird systems.
> With this scheme, the cpuinfo's reports will be smaller than before,
> and non-superfluous.

It's precisely that sort of weirdness we want to be able to catch at a glance.
These days, there is no possible way to make /proc/cpuinfo satisfy everyone and
still be compact. That's why we mostly leave it alone and put all the fun stuff
in /sys, which is much better suited to the ever-increasing complexity of modern
hardware.

If we refactor /proc/cpuinfo, it will break all sorts of things that use that
information to get an idea of what the system is running on. All of the info is
there in /sys now anyway, so if you want a different format, write your own
userspace tool to scrape it together. There's absolutely no need to implement
this purely cosmetic data formatting in the kernel.

-- Chris


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