Re: [PATCH v6 14/15] scripts/simplebench: improve ascii table: add difference line

[Max Reitz <mreitz@redhat.com>]

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On 18.09.20 20:19, Vladimir Sementsov-Ogievskiy wrote:
> Performance improvements / degradations are usually discussed in
> percentage. Let's make the script calculate it for us.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>  scripts/simplebench/simplebench.py | 46 +++++++++++++++++++++++++++---
>  1 file changed, 42 insertions(+), 4 deletions(-)
> 
> diff --git a/scripts/simplebench/simplebench.py b/scripts/simplebench/simplebench.py
> index 56d3a91ea2..0ff05a38b8 100644
> --- a/scripts/simplebench/simplebench.py
> +++ b/scripts/simplebench/simplebench.py

[...]

> +            for j in range(0, i):
> +                env_j = results['envs'][j]
> +                res_j = case_results[env_j['id']]
> +
> +                if 'average' not in res_j:
> +                    # Failed result
> +                    cell += ' --'
> +                    continue
> +
> +                col_j = chr(ord('A') + j)
> +                avg_j = res_j['average']
> +                delta = (res['average'] - avg_j) / avg_j * 100

I was wondering why you’d subtract, when percentage differences usually
mean a quotient.  Then I realized that this would usually be written as:

(res['average'] / avg_j - 1) * 100

> +                delta_delta = (res['delta'] + res_j['delta']) / avg_j * 100

Why not use the new format_percent for both cases?

> +                cell += f' {col_j}{round(delta):+}±{round(delta_delta)}%'

I don’t know what I should think about ±delta_delta.  If I saw “Compared
to run A, this is +42.1%±2.0%”, I would think that you calculated the
difference between each run result, and then based on that array
calculated average and standard deviation.

Furthermore, I don’t even know what the delta_delta is supposed to tell
you.  It isn’t even a delta_delta, it’s an average_delta.

The delta_delta would be (res['delta'] / res_j['delta'] - 1) * 100.0.
And that might be presented perhaps like “+42.1% Δ± +2.0%” (if delta
were the SD, “Δx̅=+42.1% Δσ=+2.0%” would also work; although, again, I do
interpret ± as the SD anyway).

Max


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