On 12/12/2016 01:57 PM, Florian Fainelli wrote:
OK, how would you want that to be represented? Should we try to "link"
with the leaf we are coherent with? For instance, if the L1D cache is
coherent with the L2, we have something like this:
# Assuming this is L1D cache:
/sys/devices/system/cpu/cpu0/cache/index0
ls -1
coherency_line_size
level
number_of_sets
physical_line_partition
power/
shared_cpu_list
shared_cpu_map
size
type
uevent
ways_of_associativity
We add a new symbolic link, e.g:
coherent_with -> ../index1
that indicates that this cache is coherent with the cache pointed at by
directory index1.
Thanks!
Well, I prefer the collection of 3 flags:
flush_required - or flush to next level is required to force
coherency between this level and next after update of this level
invalidate_required - or invalidate is required to force coherency
between this level and next after update of next level
coherent_to_level - object is coherent with this level (only one
domain of coherency on this level is assumed)
So, the standard MIPS L1D could be "flush_required",
"invalidate_required" and "coherent_to_level", L1I could be
"invalidate_required" and a fully coherent MIPS I6400 L1D could be just
"coherent_to_level" (no flush/invalidate required).
The reason why I don't like symlink here because it is more precise
information and it immediately pulls the question "do we need to have
horizontal links like CPU0 L1D is coherent with CPU1 L1D?" or "do we
need to have a horizontal link like CPU0 L1D is coherent with CPU1 L1I?"
or "do we have a MEMORY object?" or "what if coherency is not
bidirectional (L1D snoops L2 but not vise versa). And you should
maintain that links in case of CPU goes on/offline. And pulling info
from that link net is nontrivial in user level, especially if "lshw"
works in parallel with CPUx going offline.
But what you need is actually the answer on that 3 questions (see flags
above). At least I don't see a reason for more complicated cache level
relationship. Even the case BIG-LITTLE still is covered by flags.
- Leonid.
