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Message-ID:
<AS8PR07MB7973FA10E5A3C8AE3364471BA39BA@AS8PR07MB7973.eurprd07.prod.outlook.com>
Date: Sat, 24 May 2025 01:56:51 +0000
From: "Chia-Yu Chang (Nokia)" <chia-yu.chang@...ia-bell-labs.com>
To: Paolo Abeni <pabeni@...hat.com>, "horms@...nel.org" <horms@...nel.org>,
"donald.hunter@...il.com" <donald.hunter@...il.com>, "xandfury@...il.com"
<xandfury@...il.com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"dave.taht@...il.com" <dave.taht@...il.com>, "jhs@...atatu.com"
<jhs@...atatu.com>, "kuba@...nel.org" <kuba@...nel.org>,
"stephen@...workplumber.org" <stephen@...workplumber.org>,
"xiyou.wangcong@...il.com" <xiyou.wangcong@...il.com>, "jiri@...nulli.us"
<jiri@...nulli.us>, "davem@...emloft.net" <davem@...emloft.net>,
"edumazet@...gle.com" <edumazet@...gle.com>, "andrew+netdev@...n.ch"
<andrew+netdev@...n.ch>, "ast@...erby.net" <ast@...erby.net>,
"liuhangbin@...il.com" <liuhangbin@...il.com>, "shuah@...nel.org"
<shuah@...nel.org>, "linux-kselftest@...r.kernel.org"
<linux-kselftest@...r.kernel.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 <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
<vidhi_goel@...le.com>
Subject: RE: [PATCH v16 net-next 1/5] sched: Struct definition and parsing of
dualpi2 qdisc
> -----Original Message-----
> From: Paolo Abeni <pabeni@...hat.com>
> Sent: Tuesday, May 20, 2025 1:48 PM
> To: Chia-Yu Chang (Nokia) <chia-yu.chang@...ia-bell-labs.com>; horms@...nel.org; donald.hunter@...il.com; xandfury@...il.com; netdev@...r.kernel.org; dave.taht@...il.com; jhs@...atatu.com; kuba@...nel.org; stephen@...workplumber.org; xiyou.wangcong@...il.com; jiri@...nulli.us; davem@...emloft.net; edumazet@...gle.com; andrew+netdev@...n.ch; ast@...erby.net; liuhangbin@...il.com; shuah@...nel.org; linux-kselftest@...r.kernel.org; ij@...nel.org; ncardwell@...gle.com; Koen De Schepper (Nokia) <koen.de_schepper@...ia-bell-labs.com>; g.white <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 <vidhi_goel@...le.com>
> Subject: Re: [PATCH v16 net-next 1/5] sched: Struct definition and parsing of dualpi2 qdisc
>
>
> CAUTION: This is an external email. Please be very careful when clicking links or opening attachments. See the URL nok.it/ext for additional information.
>
>
>
> On 5/16/25 2:01 AM, chia-yu.chang@...ia-bell-labs.com wrote:
> > +static u32 calculate_probability(struct Qdisc *sch) {
> > + struct dualpi2_sched_data *q = qdisc_priv(sch);
> > + u32 new_prob;
> > + u64 qdelay_c;
> > + u64 qdelay_l;
> > + u64 qdelay;
> > + s64 delta;
> > +
> > + get_queue_delays(q, &qdelay_c, &qdelay_l);
> > + qdelay = max(qdelay_l, qdelay_c);
> > + /* Alpha and beta take at most 32b, i.e, the delay difference would
> > + * overflow for queuing delay differences > ~4.2sec.
> > + */
> > + delta = ((s64)qdelay - q->pi2_target) * q->pi2_alpha;
> > + delta += ((s64)qdelay - q->last_qdelay) * q->pi2_beta;
>
> The abov code is confusing. What do you intend to obtain with the explicit cast? the '+' left operand will be converted implicitly to unsigned as C integer implicit conversion rules.
>
Hi Paolo,
I don't fully get the '+' operator you pointed at, do you mean '-' operator?
If this is what you mean, I was thinking to change it into below, as pi2_alpha and pi2_beta are u32:
delta = ((s64)qdelay - (s64)q->pi2_target) * q->pi2_alpha;
delta += ((s64)qdelay - (s64)q->last_qdelay) * q->pi2_beta;
BRs,
Chia-Yu
> > + if (delta > 0) {
> > + new_prob = __scale_delta(delta) + q->pi2_prob;
> > + if (new_prob < q->pi2_prob)
> > + new_prob = MAX_PROB;
> > + } else {
> > + new_prob = q->pi2_prob - __scale_delta(~delta + 1);
> > + if (new_prob > q->pi2_prob)
> > + new_prob = 0;
> > + }
> > + q->last_qdelay = qdelay;
> > + /* If we do not drop on overload, ensure we cap the L4S probability to
> > + * 100% to keep window fairness when overflowing.
> > + */
> > + if (!q->drop_overload)
> > + return min_t(u32, new_prob, MAX_PROB / q->coupling_factor);
> > + return new_prob;
> > +}
> > +
> > +static u32 get_memory_limit(struct Qdisc *sch, u32 limit) {
> > + /* Apply rule of thumb, i.e., doubling the packet length,
> > + * to further include per packet overhead in memory_limit.
> > + */
> > + u64 memlim = mul_u32_u32(limit, 2 * psched_mtu(qdisc_dev(sch)));
> > +
> > + if (upper_32_bits(memlim))
> > + return 0xffffffff;
>
> Pleas use U32_MAX.
>
> [...]
> > +static int dualpi2_change(struct Qdisc *sch, struct nlattr *opt,
> > + struct netlink_ext_ack *extack) {
> > + struct nlattr *tb[TCA_DUALPI2_MAX + 1];
> > + struct dualpi2_sched_data *q;
> > + int old_backlog;
> > + int old_qlen;
> > + int err;
> > +
> > + if (!opt)
> > + return -EINVAL;
> > + err = nla_parse_nested(tb, TCA_DUALPI2_MAX, opt, dualpi2_policy,
> > + extack);
> > + if (err < 0)
> > + return err;
> > +
> > + q = qdisc_priv(sch);
> > + sch_tree_lock(sch);
> > +
> > + if (tb[TCA_DUALPI2_LIMIT]) {
> > + u32 limit = nla_get_u32(tb[TCA_DUALPI2_LIMIT]);
> > +
> > + WRITE_ONCE(sch->limit, limit);
> > + WRITE_ONCE(q->memory_limit, get_memory_limit(sch, limit));
> > + }
> > +
> > + if (tb[TCA_DUALPI2_MEMORY_LIMIT])
> > + WRITE_ONCE(q->memory_limit,
> > + nla_get_u32(tb[TCA_DUALPI2_MEMORY_LIMIT]));
> > +
> > + if (tb[TCA_DUALPI2_TARGET]) {
> > + u64 target = nla_get_u32(tb[TCA_DUALPI2_TARGET]);
> > +
> > + WRITE_ONCE(q->pi2_target, target * NSEC_PER_USEC);
> > + }
> > +
> > + if (tb[TCA_DUALPI2_TUPDATE]) {
> > + u64 tupdate = nla_get_u32(tb[TCA_DUALPI2_TUPDATE]);
> > +
> > + WRITE_ONCE(q->pi2_tupdate, convert_us_to_nsec(tupdate));
> > + }
> > +
> > + if (tb[TCA_DUALPI2_ALPHA]) {
> > + u32 alpha = nla_get_u32(tb[TCA_DUALPI2_ALPHA]);
> > +
> > + WRITE_ONCE(q->pi2_alpha, dualpi2_scale_alpha_beta(alpha));
> > + }
> > +
> > + if (tb[TCA_DUALPI2_BETA]) {
> > + u32 beta = nla_get_u32(tb[TCA_DUALPI2_BETA]);
> > +
> > + WRITE_ONCE(q->pi2_beta, dualpi2_scale_alpha_beta(beta));
> > + }
> > +
> > + if (tb[TCA_DUALPI2_STEP_THRESH]) {
> > + u32 step_th = nla_get_u32(tb[TCA_DUALPI2_STEP_THRESH]);
> > + bool step_pkt =
> > + nla_get_flag(tb[TCA_DUALPI2_STEP_PACKETS]);
> > +
> > + WRITE_ONCE(q->step_in_packets, step_pkt);
> > + WRITE_ONCE(q->step_thresh,
> > + step_pkt ? step_th : convert_us_to_nsec(step_th));
> > + }
> > +
> > + if (tb[TCA_DUALPI2_MIN_QLEN_STEP])
> > + WRITE_ONCE(q->min_qlen_step,
> > + nla_get_u32(tb[TCA_DUALPI2_MIN_QLEN_STEP]));
> > +
> > + if (tb[TCA_DUALPI2_COUPLING]) {
> > + u8 coupling = nla_get_u8(tb[TCA_DUALPI2_COUPLING]);
> > +
> > + WRITE_ONCE(q->coupling_factor, coupling);
> > + }
> > +
> > + if (tb[TCA_DUALPI2_DROP_OVERLOAD]) {
> > + u8 drop_overload =
> > + nla_get_u8(tb[TCA_DUALPI2_DROP_OVERLOAD]);
> > +
> > + WRITE_ONCE(q->drop_overload, (bool)drop_overload);
> > + }
> > +
> > + if (tb[TCA_DUALPI2_DROP_EARLY]) {
> > + u8 drop_early = nla_get_u8(tb[TCA_DUALPI2_DROP_EARLY]);
> > +
> > + WRITE_ONCE(q->drop_early, (bool)drop_early);
> > + }
> > +
> > + if (tb[TCA_DUALPI2_C_PROTECTION]) {
> > + u8 wc = nla_get_u8(tb[TCA_DUALPI2_C_PROTECTION]);
> > +
> > + dualpi2_calculate_c_protection(sch, q, wc);
> > + }
> > +
> > + if (tb[TCA_DUALPI2_ECN_MASK]) {
> > + u8 ecn_mask = nla_get_u8(tb[TCA_DUALPI2_ECN_MASK]);
> > +
> > + WRITE_ONCE(q->ecn_mask, ecn_mask);
> > + }
> > +
> > + if (tb[TCA_DUALPI2_SPLIT_GSO]) {
> > + u8 split_gso = nla_get_u8(tb[TCA_DUALPI2_SPLIT_GSO]);
> > +
> > + WRITE_ONCE(q->split_gso, (bool)split_gso);
> > + }
> > +
> > + old_qlen = qdisc_qlen(sch);
> > + old_backlog = sch->qstats.backlog;
> > + while (qdisc_qlen(sch) > sch->limit ||
> > + q->memory_used > q->memory_limit) {
> > + struct sk_buff *skb = __qdisc_dequeue_head(&sch->q);
>
> As per commit 2d3cbfd6d54a2c39ce3244f33f85c595844bd7b8, the above should be:
>
> struct sk_buff *skb = qdisc_dequeue_internal(sch, true);
>
> /P
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