netdev - Re: [RFC PATCH] net/sched: add indirect call wrapper hint.

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Date:   Thu, 18 Jun 2020 12:00:13 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [RFC PATCH] net/sched: add indirect call wrapper hint.



On 6/18/20 10:31 AM, Paolo Abeni wrote:
> The sched layer can use several indirect calls per
> packet, with not work-conservative qdisc being
> more affected due to the lack of the BYPASS path.
> 
> This change tries to improve the situation using
> the indirect call wrappers infrastructure for the
> qdisc enqueue end dequeue indirect calls.
> 
> To cope with non-trivial scenarios, a compile-time know is
> introduced, so that the qdisc used by ICW can be different
> from the default one.
> 
> Tested with pktgen over qdisc, with CONFIG_HINT_FQ_CODEL=y:
> 
> qdisc		threads vanilla	patched delta
> 		nr	Kpps	Kpps	%
> pfifo_fast	1	3300	3700	12
> pfifo_fast	2	3940	4070	3
> fq_codel	1	3840	4110	7
> fq_codel	2	1920	2260	17
> fq		1	2230	2210	-1
> fq		2	1530	1540	1

Hi Paolo

This test is a bit misleading, pktgen has a way to bypass the qdisc.

Real numbers for more typical workloads would be more appealing,
before we consider a quite invasive patch ?

What is the status of static_call infrastructure ?


>  
> +#ifndef CODEL_SCOPE
> +#define CODEL_SCOPE static
> +#endif

This looks additional burden, just remove the static attribute,
if a function might be called directly.

Eg, we have EXPORT_SYMBOL() all over the places, even if the modules needing
a symbol might not be compiled at all, or being part of vmlinux.

Thanks !