Re: [Qemu-devel] [PATCH 1/7] virtio: allow byte swapping for vring and config access

[Rusty Russell]

Anthony Liguori <address@hidden> writes:
> Rusty Russell <address@hidden> writes:
>> (Qemu run under eatmydata to eliminate syncs)
>
> FYI, cache=unsafe is equivalent to using eatmydata.

Ah, thanks!

> I can reproduce this although I also see a larger standard deviation.
>
> BEFORE:
>       MIN: 496
>       MAX: 1055
>         AVG: 873.22
>         STDEV: 136.88
>
> AFTER:
>         MIN: 494
>         MAX: 1456
>         AVG: 947.77
>         STDEV: 150.89

BTW, how did you generate these stats?  Consider this my plug for my
little stats filter:
        https://github.com/rustyrussell/stats

>
> In my datasets, the stdev is higher in the after case implying that
> there is more variation.  Indeed, the MIN is pretty much the same.
>
> GCC is inlining the functions, I'm still surprised that it's measurable
> at all.

GCC won't inline across compilation units without -flto though, so the
stub call won't be inlined, right?

Cheers,
Rusty.