Re: [PATCH] Reading deterministic cache parameters and exporting it in /sysfs

[Dave Jones]

On Tue, Mar 15, 2005 at 03:24:48PM -0800, Venkatesh Pallipadi wrote:
 >  
 > The attached patch adds support for using cpuid(4) instead of cpuid(2), to get 
 > CPU cache information in a deterministic way for Intel CPUs, whenever 
 > supported. The details of cpuid(4) can be found here
 > 
 > IA-32 Intel Architecture Software Developer's Manual (vol 2a)
 > (http://developer.intel.com/design/pentium4/manuals/index_new.htm#sdm_vol2a)
 > and
 > Prescott New Instructions (PNI) Technology: Software Developer's Guide
 > (http://www.intel.com/cd/ids/developer/asmo-na/eng/events/43988.htm)
 >  
 > The advantage of using the cpuid(4) ('Deterministic Cache Parameters Leaf') are:
 > * It provides more information than the descriptors provided by cpuid(2)
 > * It is not table based as cpuid(2). So, we will not need changes to the 
 >   kernel to support new cache descriptors in the descriptor table (as is the 
 >   case with cpuid(2)).
 >  
 > The patch also adds a bunch of interfaces under 
 > /sys/devices/system/cpu/cpuX/cache, showing various information about the
 > caches.

Why does this need to be in kernel-space ? Is there some reason that prevents
you from enhancing x86info for example ?  I really want to live to see the
death of /proc/cpuinfo one day, and reinventing it in sysfs seems pointless
if it can all be done in userspace.
 
 > Most useful field being shared_cpu_map, which says what caches are 
 > shared among which logical cpus. 

Given that the most useful field is of limited use to a majority of users,
and those that are interested can read this from userspace, this has me very puzzled.

		Dave

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