Re: [Qemu-devel] [PATCH 02/10] compiler.h: add QEMU_CACHELINE + QEMU_ALIGN() + QEMU_CACHELINE_ALIGNED

[Lluís Vilanova]

Peter Maydell writes:

> On 5 April 2016 at 13:57, Lluís Vilanova <address@hidden> wrote:
>> Emilio G Cota writes:
>> 
>>> I'm assuming windows compilers don't support this attribute.
>>> Signed-off-by: Emilio G. Cota <address@hidden>
>>> ---
>>> include/qemu/compiler.h | 10 ++++++++++
>>> 1 file changed, 10 insertions(+)
>> 
>>> diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
>>> index 8f1cc7b..fb946f1 100644
>>> --- a/include/qemu/compiler.h
>>> +++ b/include/qemu/compiler.h
>>> @@ -41,6 +41,16 @@
>>> # define QEMU_PACKED __attribute__((packed))
>>> #endif
>> 
>>> +#define QEMU_CACHELINE (64)
>> [...]
>> 
>> You should make this a value taken from configure. In linux you could use
>> something like:
>> 
>> getconf LEVEL1_DCACHE_LINESIZE
>> 
>> Or an equivalent program using sysconf(3) if getconf is not present.

> The cache line size at compile time is not necessarily the cache
> line size at runtime...

True, but exposing it as a configure flag allows tunning for the target arch
during cross-compilation. It would be bettwe to use the compiler to tell you
about the target cache line size, but I'm not aware of a way to do it.

Got it!

  gcc -march=native --help=params -v 2>&1 | grep "param l1-cache-line-size" | 
sed -e 's/.* --param l1-cache-line-size=\([0-9]\+\) .*/\1/'


Cheers,
  Lluis