From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it1-x130.google.com (mail-it1-x130.google.com [IPv6:2607:f8b0:4864:20::130]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id 85A153B29E for ; Sat, 16 Feb 2019 04:35:42 -0500 (EST) Received: by mail-it1-x130.google.com with SMTP id i2so29419821ite.5 for ; Sat, 16 Feb 2019 01:35:42 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=0XEUlFy81amveKaEXVhmfeY208lugipUAeoH+T00++M=; b=fQrsafqqDDB7aibIkaY74QZgrxm5PFT7lRdrmuDcX9kPqrIz4GqL76AM8Qfcz6sfcm yOv8/ebZCaxtDhXlAt5VmpchcKuN8tVGRq4kJPmXZx/650rjg77+jAwLO6Q+U1RP6FQj BgXFS0FfLopLKu6N0+gqUhKbkIBPEzNcivahVlD6pCOfgD9kfIivDsTc1clCeO+B0xuz cwJ2ECYoCUdpVWvqebWEPgfyk05tJmKCV0g1f5Q+6WhQSwk7DhYn1LxCA9fSIKfJIHm9 id5itBTzjVV5y1Nq9vrYTtPO4bJaJfoVvb1tmHfrv2GIRdK0cRw5n6QzeuNYRRw/TS5Y yfIA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=0XEUlFy81amveKaEXVhmfeY208lugipUAeoH+T00++M=; b=r7AeU36XPhYePHe1DeZKYW/7iIG/8o3OnPot/u3FY1G2xxafHPsfWnUTNNWOm+mIPM oJHKvqgson/IE24VQqEKBxp06rfOdbkCB+Vwich+89vP2wiNP43iIHLwwZxFTz7y+qjK Uzj5hHOok7s7CzgZ2RCFl9kqjrwB8IaPhEwWfZ/hqYx3p/awnkftXvbvE4pHXluLgLlT WEP42J62guHhgL1m3qJEtmiA2Y3N4M9+3F5WnHXpYSVvjsem/FbxfrfrUocxv/ip5gGS qodXm+a0Q3CC0Xsdh/3xgV7dQeWVpwvDaVQpKvjFz4irW1jLNL1RUygJGn3NKrPwHSrd U7Zw== X-Gm-Message-State: AHQUAuZ1VO9sFaA9x+NwdLPUv/pzEUW5apBWJrIx4dNnuU6zBKg/9wCi xXs3XPSYpHB4QEz97N90mCNWLvg3qKdgBRklbAA= X-Google-Smtp-Source: AHgI3IZsAihJnj1tedHCaGVJYA8XQARGxa2p2CZOQ/vPtlPYaaE5EuNmFXqW4PPe6rfmPLWV3P2B0r6BkKMOHiKUOQ0= X-Received: by 2002:a05:660c:d4:: with SMTP id q20mr7840021itk.21.1550309742064; Sat, 16 Feb 2019 01:35:42 -0800 (PST) MIME-Version: 1.0 References: In-Reply-To: From: Adrian Popescu Date: Sat, 16 Feb 2019 11:35:30 +0200 Message-ID: To: Dave Taht Cc: Cake List Content-Type: multipart/alternative; boundary="00000000000077b9ca0581ff9d85" Subject: Re: [Cake] Dropping dropped X-BeenThere: cake@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: Cake - FQ_codel the next generation List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 16 Feb 2019 09:35:42 -0000 --00000000000077b9ca0581ff9d85 Content-Type: text/plain; charset="UTF-8" Hello, On Fri, Feb 15, 2019 at 10:45 PM Dave Taht wrote: > I still regard inbound shaping as our biggest deployment problem, > especially on cheap hardware. > > Some days I want to go back to revisiting the ideas in the "bobbie" > shaper, other days... > > In terms of speeding up cake: > > * At higher speeds (e.g. > 200mbit) cake tends to bottleneck on a > single cpu, in softirq. A lwn article just went by about a proposed > set of improvements for that: > https://lwn.net/SubscriberLink/779738/771e8f7050c26ade/ Will this help devices with a single core CPU? > > > * Hardware multiqueue is more and more common (APU2 has 4). FQ_codel > is inherently parallel and could take advantage of hardware > multiqueue, if there was a better way to express it. What happens > nowadays is you get the "mq" scheduler with 4 fq_codel instances, when > running at line rate, but I tend to think with 64 hardware queues, > increasingly common in the >10GigE, having 64k fq_codel queues is > excessive. I'd love it if there was a way to have there be a divisor > in the mq -> subqdisc code so that we would have, oh, 32 queues per hw > queue in this case. > > Worse, there's no way to attach a global shaped instance to that > hardware, e.g. in cake, which forces all those hardware queues (even > across cpus) into one. The ingress mirred code, here, is also a > problem. a "cake-mq" seemed feasible (basically you just turn the > shaper tracking into an atomic operation in three places), but the > overlying qdisc architecture for sch_mq -> subqdiscs has to be > extended or bypassed, somehow. (there's no way for sch_mq to > automagically pass sub-qdisc options to the next qdisc, and there's no > reason to have sch_mq > The problem I deal with is performance on even lower end hardware with a single queue. My experience with mq has been limited. > > * I really liked the ingress "skb list" rework, but I'm not sure how > to get that from A to B. > What was this skb list rework? Is there a patch somewhere? > > * and I have a long standing dream of being able to kill off mirred > entirely and just be able to write > > tc qdisc add dev eth0 ingress cake bandwidth X > Ingress on its own seems to be a performance hit. Do you think this would reduce the performance hit? > > * native codel is 32 bit, cake is 64 bit. I > Was there something else you forgot to write here? > > * hashing three times as cake does is expensive. Getting a partial > hash and combining it into a final would be faster. > Could you elaborate how this would look, please? I've read the code a while ago. It might be that I didn't figure out all the places where hashing is done. > > * 8 way set associative is slower than 4 way and almost > indistinguishable from 8. Even direct mapping > This should be easy to address by changing the 8 ways to to 4. Was there something else you wanted to write here? > > * The cake blue code is rarely triggered and inline > > I really did want cake to be faster than htb+fq_codel, I started a > project to basically ressurrect "early cake" - which WAS 40% faster > than htb+fq_codel and add in the idea *only* of an atomic builtin > hw-mq shaper a while back, but haven't got back to it. > > https://github.com/dtaht/fq_codel_fast > > with everything I ripped out in that it was about 5% less cpu to start > with. > Perhaps further improvements made to the codel_vars struct will also help fq_codel_fast. Do you think this could be improved further? A cake_fast might be worth a shot. > > I can't tell you how many times I've looked over > > https://elixir.bootlin.com/linux/latest/source/net/sched/sch_mqprio.c > > hoping that enlightment would strike and there was a clean way to get > rid of that layer of abstraction. > > But coming up with how to run more stuff in parallel was beyond my rcu-foo. > --00000000000077b9ca0581ff9d85 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Hello,

On Fri, Feb 15, 2019 at 10:45 PM Dave Taht = <dave.taht@gmail.com> wrot= e:
I still regar= d inbound shaping as our biggest deployment problem,
especially on cheap hardware.

Some days I want to go back to revisiting the ideas in the "bobbie&quo= t;
shaper, other days...

In terms of speeding up cake:

* At higher speeds (e.g. > 200mbit) cake tends to bottleneck on a
single cpu, in softirq. A lwn article just went by about a proposed
set of improvements for that:
https://lwn.net/SubscriberLink/779738/771e8f7= 050c26ade/
Will this help devices with a single core C= PU?
=C2=A0


* Hardware multiqueue is more and more common (APU2 has 4). FQ_codel
is inherently parallel and could take advantage of hardware
multiqueue, if there was a better way to express it. What happens
nowadays is you get the "mq" scheduler with 4 fq_codel instances,= when
running at line rate, but I tend to think with 64 hardware queues,
increasingly common in the >10GigE, having 64k fq_codel queues is
excessive. I'd love it if there was a way to have there be a divisor in the mq -> subqdisc code so that we would have, oh, 32 queues per hw queue in this case.

Worse, there's no way to attach a global shaped instance to that
hardware, e.g. in cake, which forces all those hardware queues (even
across cpus) into one. The ingress mirred code, here, is also a
problem. a "cake-mq" seemed feasible (basically you just turn the=
shaper tracking into an atomic operation in three places), but the
overlying qdisc architecture for sch_mq -> subqdiscs has to be
extended or bypassed, somehow. (there's no way for sch_mq to
automagically pass sub-qdisc options to the next qdisc, and there's no<= br> reason to have sch_mq

The problem I dea= l with is performance on even lower end hardware with a single queue. My ex= perience with mq has been limited.
=C2=A0

* I really liked the ingress "skb list" rework, but I'm not s= ure how
to get that from A to B.

What was this = skb list rework? Is there a patch somewhere?
=C2=A0

* and I have a long standing dream of being able to kill off mirred
entirely and just be able to write

tc qdisc add dev eth0 ingress cake bandwidth X

Ingress on its own seems to be a performance hit. Do you think this= would reduce the performance hit?
=C2=A0

*=C2=A0 native codel is 32 bit, cake is 64 bit. I

=
Was there something else you forgot to write here?
=C2=A0

* hashing three times as cake does is expensive. Getting a partial
hash and combining it into a final would be faster.
Could you elaborate how this would look, please? I've read= the code a while ago. It might be that I didn't figure out all the pla= ces where hashing is done.
=C2=A0

* 8 way set associative is slower than 4 way and almost
indistinguishable from 8. Even direct mapping

This should be easy to address by changing the 8 ways to to 4. Was t= here something else you wanted to write here?
=C2=A0

* The cake blue code is rarely triggered and inline

I really did want cake to be faster than htb+fq_codel, I started a
project to basically ressurrect "early cake" - which WAS 40% fast= er
than htb+fq_codel and add in the idea *only* of an atomic builtin
hw-mq shaper a while back, but haven't got back to it.

https://github.com/dtaht/fq_codel_fast

with everything I ripped out in that it was about 5% less cpu to start with= .

Perhaps further improvements made to = the codel_vars struct will also help fq_codel_fast. Do you think this could= be improved further?

A cake_fast might be worth a= shot.
=C2=A0

I can't tell you how many times I've looked over

https://elixir.bootlin.com/linu= x/latest/source/net/sched/sch_mqprio.c

hoping that enlightment would strike and there was a clean way to get
rid of that layer of abstraction.

But coming up with how to run more stuff in parallel was beyond my rcu-foo.=
--00000000000077b9ca0581ff9d85--