On Tue, Apr 05, 2016 at 08:57:45 +0100, Peter Maydell wrote:
> On 5 April 2016 at 06:30, Emilio G. Cota <c...@braap.org> wrote:
> > +#define QEMU_CACHELINE (64)
>
> Why 64? Does anything bad happen if the host's cache line
> size turns out to be greater than the value here ?
Defining a number lower than the host's cache line could result
in some false sharing. No big deal for most workloads.
Defining a number greater than the host's cache might result in
wasted memory, which we really should avoid.
I used 64 because it is common on x86, which I assume is what most
developers develop on.
On Tue, Apr 05, 2016 at 17:29:05 +0200, Paolo Bonzini wrote:
> But the size of data structures cannot change at run-time. A bigger
> worry is cross-compilation.
>
> Linux has these defaults:
>
> Alpha 32 or 64
> ARM configurable, 64 for ARMv7
> AArch64 128
> PPC 128
> s390 256
> x86 configurable, default 64
>
> which should be easy to copy in QEMU too.
So how about this:
we add these defaults, and also add an optional --configure
parameter to override said defaults.
Otherwise I'd just stick to 64.
Thanks,
Emilio
