[ltt-dev] liburcu cache line size

[david.goulet@polymtl.ca (David Goulet)]

Hi,

I have some doubt about the value of #define CACHE_LINE_SIZE 
(urcu/arch_x86.h) that is set to 128.

After some research and looking on my computer, the x86 architecture 
seems to have most of the time 64 bytes size. On my i7 920, here's what 
I have :

# getconf LEVEL1_DCACHE_LINESIZE
64

# cat /sys/devices/system/cpu/cpu0/cache/index0/coherency_line_size
64

Since the Intel NetBurst microarch., the Intel manual says 64 bytes also 
and it has not changed apparently for Nehalem.

So, Mathieu, why 128 bytes? UST is using that, if it's the wrong value 
here for x86, it could have an effect on cache pressure since 2 lines 
are required for structure less then 64 bytes.

Thanks!
-- 
David Goulet
LTTng project, DORSAL Lab.

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