Benjamin LaHaise a écrit :
On Mon, Mar 12, 2007 at 02:08:18PM -0700, Stephen Hemminger wrote:
For Eric, mark packet type and network device watermarks
as read mostly.
The following x86-64 bits might be intersting, as they allow you to
completely eliminate the memory access for run time defined constants.
Note that read_always writes are non-atomic, so some other form of
protection is necessary for readers (and rcu won't cut it). That can be
fixed somewhat by specifying the alignment for the mov instruction to
ensure writes are atomic, but for many uses that is overkill. This kind
of change can make the biggest difference for high-latency cases, like L1
cache misses on the Prescott P4. I've not benched it on a P4 of late,
though.
Very very nice idea Ben !
However netdev_nit is not a good condidate because it might change quite often
in fact :(
Clearly kmem_cache pointers are very good candidates.
One problem with your patch is that all read_always() of pointers are going to
use 3 bytes more of code, thus raising icache pressure.
48 b8 c3 08 e8 8c af mov $0x71af8ce808c3,%rax
71 00 00
instead of %rip relative addressing
48 8b 05 99 f3 09 00 mov 652185(%rip),%rax
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