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Bug 59634 - Documentation (info/man page): lack of information for cache size parameters (--param)
Summary: Documentation (info/man page): lack of information for cache size parameters ...
Status: UNCONFIRMED
Alias: None
Product: gcc
Classification: Unclassified
Component: middle-end (show other bugs)
Version: unknown
: P3 normal
Target Milestone: ---
Assignee: Not yet assigned to anyone
URL:
Keywords: documentation
Depends on:
Blocks:
 
Reported: 2013-12-30 17:11 UTC by ytrezq
Modified: 2016-10-07 08:20 UTC (History)
1 user (show)

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Description ytrezq 2013-12-30 17:11:07 UTC
gcc have several --param for suggesting cache size (l1-cache-line-size l1-cache-size l2-cache-size)


However some processors/SoC (like the BCM6358) have separates caches for instructions and data. The documentation don't say which size to consider.
For example if you have a processor where you get those info with dmesg:

"Primary instruction cache 32kB, VIPT, 2-way, linesize 16 bytes" and "Primary data cache 16kB, 2-way, VIPT, cache aliases, linesize 16 bytes"

You know the value for --param l1-cache-line-size is 16 but for l1-cache-size you don't know if it is 32Kb or 16Kb.
Comment 1 Andrew Pinski 2013-12-30 19:23:20 UTC
http://gcc.gnu.org/onlinedocs/gcc-4.8.2/gcc/Optimize-Options.html#index-param-935

l1-cache-line-size
The size of cache line in L1 cache, in bytes. 
l1-cache-size
The size of L1 cache, in kilobytes. 
l2-cache-size
The size of L2 cache, in kilobytes. 

This is talking about data cache size.
Comment 2 ytrezq 2013-12-30 19:59:48 UTC
Ok. So, does it worth to make a change to the documentation?

An another possibility it to rename the parameter in this way:

l1-cache-size	-->	l1-data-cache-size
l2-cache-size	-->	l2-data-cache-size