netdev - RE: [PATCH v4 net-next 1/1] sched: Add dualpi2 qdisc

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID:
 <AM9PR07MB7969E939CA6C563F9A4061B4A34B2@AM9PR07MB7969.eurprd07.prod.outlook.com>
Date: Tue, 29 Oct 2024 15:27:03 +0000
From: "Chia-Yu Chang (Nokia)" <chia-yu.chang@...ia-bell-labs.com>
To: Paolo Abeni <pabeni@...hat.com>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>, "davem@...emloft.net" <davem@...emloft.net>,
	"stephen@...workplumber.org" <stephen@...workplumber.org>, "jhs@...atatu.com"
	<jhs@...atatu.com>, "edumazet@...gle.com" <edumazet@...gle.com>,
	"kuba@...nel.org" <kuba@...nel.org>, "dsahern@...nel.org"
	<dsahern@...nel.org>, "ij@...nel.org" <ij@...nel.org>, "ncardwell@...gle.com"
	<ncardwell@...gle.com>, "Koen De Schepper (Nokia)"
	<koen.de_schepper@...ia-bell-labs.com>, "g.white@...leLabs.com"
	<g.white@...leLabs.com>, "ingemar.s.johansson@...csson.com"
	<ingemar.s.johansson@...csson.com>, "mirja.kuehlewind@...csson.com"
	<mirja.kuehlewind@...csson.com>, "cheshire@...le.com" <cheshire@...le.com>,
	"rs.ietf@....at" <rs.ietf@....at>, "Jason_Livingood@...cast.com"
	<Jason_Livingood@...cast.com>, "vidhi_goel@...le.com" <vidhi_goel@...le.com>
CC: Olga Albisser <olga@...isser.org>, "Olivier Tilmans (Nokia)"
	<olivier.tilmans@...ia.com>, Henrik Steen <henrist@...rist.net>, Bob Briscoe
	<research@...briscoe.net>
Subject: RE: [PATCH v4 net-next 1/1] sched: Add dualpi2 qdisc

Pls see below

Best regards,
Chia-Yu

> -----Original Message-----
> From: Paolo Abeni <pabeni@...hat.com> 
> Sent: Tuesday, October 29, 2024 1:56 PM
> To: Chia-Yu Chang (Nokia) <chia-yu.chang@...ia-bell-labs.com>; netdev@...r.kernel.org; davem@...emloft.net; stephen@...workplumber.org; jhs@...atatu.com; edumazet@...gle.com; kuba@...nel.org; dsahern@...nel.org; ij@...nel.org; ncardwell@...gle.com; Koen De Schepper (Nokia) <koen.de_schepper@...ia-bell-labs.com>; g.white@...leLabs.com; ingemar.s.johansson@...csson.com; mirja.kuehlewind@...csson.com; cheshire@...le.com; rs.ietf@....at; Jason_Livingood@...cast.com; vidhi_goel@...le.com
> Cc: Olga Albisser <olga@...isser.org>; Olivier Tilmans (Nokia) <olivier.tilmans@...ia.com>; Henrik Steen <henrist@...rist.net>; Bob Briscoe <research@...briscoe.net>
> Subject: Re: [PATCH v4 net-next 1/1] sched: Add dualpi2 qdisc


On 10/22/24 00:12, chia-yu.chang@...ia-bell-labs.com wrote:
>> +/* Default alpha/beta values give a 10dB stability margin with 
>> +max_rtt=100ms. */ static void dualpi2_reset_default(struct 
>> +dualpi2_sched_data *q) {
>> +     q->sch->limit = 10000;                          /* Max 125ms at 1Gbps */
>> +
>> +     q->pi2.target = 15 * NSEC_PER_MSEC;
>> +     q->pi2.tupdate = 16 * NSEC_PER_MSEC;
>> +     q->pi2.alpha = dualpi2_scale_alpha_beta(41);    /* ~0.16 Hz * 256 */
>> +     q->pi2.beta = dualpi2_scale_alpha_beta(819);    /* ~3.20 Hz * 256 */
>> +
>> +     q->step.thresh = 1 * NSEC_PER_MSEC;
>> +     q->step.in_packets = false;
>> +
>> +     dualpi2_calculate_c_protection(q->sch, q, 10);  /* wc=10%, 
>> + wl=90% */
>> +
>> +     q->ecn_mask = INET_ECN_ECT_1;
>> +     q->coupling_factor = 2;         /* window fairness for equal RTTs */
>> +     q->drop_overload = true;        /* Preserve latency by dropping */
>> +     q->drop_early = false;          /* PI2 drops on dequeue */
>> +     q->split_gso = true;

> This is a very unexpected default. Splitting GSO packets earlier WRT the H/W constaints definitely impact performances in a bad way.

> Under which condition this is expected to give better results?
> It should be at least documented clearly.

> Thanks,

> Paolo

I see a similar operation exists in other qdisc (e.g., sch_tbf.c and sch_cake). They both walk through segs of skb_list.
Instead, I see other qdisc use "skb_list_walk_safe" macro, so I was thinking to follow a similar approach in dualpi2 (or other comments please let me know).
Or do you suggest we should force gso-splitting like in other qdisc?

Chia-Yu