From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <kuba@kernel.org>
Received: from nyc.source.kernel.org (nyc.source.kernel.org [147.75.193.91])
 (using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits))
 (No client certificate requested)
 by lists.bufferbloat.net (Postfix) with ESMTPS id 599A83B29D
 for <cake@lists.bufferbloat.net>; Fri,  6 Sep 2024 21:14:17 -0400 (EDT)
Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58])
 by nyc.source.kernel.org (Postfix) with ESMTP id A3F32A43B4A;
 Sat,  7 Sep 2024 01:14:09 +0000 (UTC)
Received: by smtp.kernel.org (Postfix) with ESMTPSA id 46BCAC4CEC4;
 Sat,  7 Sep 2024 01:14:16 +0000 (UTC)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org;
 s=k20201202; t=1725671656;
 bh=wf51T13dH53Kyjr9k6X4rECRSev9KzFZmG/yaTpBkVo=;
 h=Date:From:To:Cc:Subject:In-Reply-To:References:From;
 b=DkHLATM+cQka/l4F4KRRYxp7D456XNqh0W+W6SFpZU/mIByFNDGDwiV4JigTEY14P
 Yux8T0xXHh3TtYfNqNsdeXKp3JlAysw4ypCnJgvcrHwN7+6gQIYrbYoSqK6rjXwKMM
 XY3KXwxZ8eDdV0i7T5n1GCVPyU28Id6ARxh66KZaqHx1y+9Qv/mYA9wV6YFjn3UJ8T
 M+q2Nmmqqumhz+9IB2MbYatQczwi9yV/aGKVSlcUFX7Op0HBnsK2/f53JJp811cGJL
 a6Ufdnfsvxwcsc4k/HrAFVSI4FqTIx6RXZEaazusyO1epdMyC1ANXyqp1MYrBiSXoK
 8HnDqJU81Xj1A==
Date: Fri, 6 Sep 2024 18:14:15 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Toke =?UTF-8?B?SMO4aWxhbmQtSsO4cmdlbnNlbg==?= <toke@redhat.com>
Cc: Toke =?UTF-8?B?SMO4aWxhbmQtSsO4cmdlbnNlbg==?= <toke@toke.dk>, Jamal Hadi
 Salim <jhs@mojatatu.com>, Cong Wang <xiyou.wangcong@gmail.com>, Jiri Pirko
 <jiri@resnulli.us>, Dave Taht <dave.taht@gmail.com>, "David S. Miller"
 <davem@davemloft.net>, Eric Dumazet <edumazet@google.com>, Paolo Abeni
 <pabeni@redhat.com>, cake@lists.bufferbloat.net, netdev@vger.kernel.org
Message-ID: <20240906181415.11d34150@kernel.org>
In-Reply-To: <20240904100516.16926-1-toke@redhat.com>
References: <20240904100516.16926-1-toke@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
Subject: Re: [Cake] [PATCH net-next] sch_cake: constify inverse square root
	cache
X-BeenThere: cake@lists.bufferbloat.net
X-Mailman-Version: 2.1.20
Precedence: list
List-Id: Cake - FQ_codel the next generation <cake.lists.bufferbloat.net>
List-Unsubscribe: <https://lists.bufferbloat.net/options/cake>,
 <mailto:cake-request@lists.bufferbloat.net?subject=unsubscribe>
List-Archive: <https://lists.bufferbloat.net/pipermail/cake>
List-Post: <mailto:cake@lists.bufferbloat.net>
List-Help: <mailto:cake-request@lists.bufferbloat.net?subject=help>
List-Subscribe: <https://lists.bufferbloat.net/listinfo/cake>,
 <mailto:cake-request@lists.bufferbloat.net?subject=subscribe>
X-List-Received-Date: Sat, 07 Sep 2024 01:14:17 -0000

On Wed,  4 Sep 2024 12:05:16 +0200 Toke H=C3=B8iland-J=C3=B8rgensen wrote:
> +/* There is a big difference in timing between the accurate values place=
d in the
> + * cache and the approximations given by a single Newton step for small =
count
> + * values, particularly when stepping from count 1 to 2 or vice versa. H=
ence,
> + * these values are calculated using eight Newton steps, using the imple=
mentation
> + * below. Above 16, a single Newton step gives sufficient accuracy in ei=
ther
> + * direction, given the precision stored.

Please line wrap the comments at 80 chars.

> + * The magnitude of the error when stepping up to count 2 is such as to =
give
> + * the value that *should* have been produced at count 4.
> + */
> +
>  #define REC_INV_SQRT_CACHE (16)
> -static u32 cobalt_rec_inv_sqrt_cache[REC_INV_SQRT_CACHE] =3D {0};
> +static const u32 inv_sqrt_cache[REC_INV_SQRT_CACHE] =3D {
> +	        ~0,         ~0, 3037000500, 2479700525,
> +	2147483647, 1920767767, 1753413056, 1623345051,
> +	1518500250, 1431655765, 1358187914, 1294981364,
> +	1239850263, 1191209601, 1147878294, 1108955788

checkpatch asks to use tabs to indent the ~0, which seems fair
--=20
pw-bot: cr