netdev - Re: [PATCH net-next v3 2/8] taprio: Add support for frame preemption offload

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Date:   Fri, 29 Jan 2021 15:12:58 -0800
From:   Vinicius Costa Gomes <vinicius.gomes@...el.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Vladimir Oltean <vladimir.oltean@....com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "jhs@...atatu.com" <jhs@...atatu.com>,
        "xiyou.wangcong@...il.com" <xiyou.wangcong@...il.com>,
        "jiri@...nulli.us" <jiri@...nulli.us>,
        "Jose.Abreu@...opsys.com" <Jose.Abreu@...opsys.com>,
        Po Liu <po.liu@....com>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        "anthony.l.nguyen@...el.com" <anthony.l.nguyen@...el.com>,
        "mkubecek@...e.cz" <mkubecek@...e.cz>
Subject: Re: [PATCH net-next v3 2/8] taprio: Add support for frame
 preemption offload

Jakub Kicinski <kuba@...nel.org> writes:
>> > First I'm interested in the means: why check for preempt == U32_MAX when
>> > you determine that all traffic classes are preemptible? What if less
>> > than 32 traffic classes are used by the netdev? The check will be
>> > bypassed, won't it?  
>> 
>> Good catch :-)
>> 
>> I wanted to have this (at least one express queue) handled in a
>> centralized way, but perhaps this should be handled best per driver.
>
> Centralized is good. Much easier than reviewing N drivers to make sure
> they all behave the same, and right.

The issue is that it seems that not all drivers/hw have the same
limitation: that at least one queue needs to be configured as
express/not preemptible.

That's the point I was trying to make when I suggested for the check to
be done per-driver, different limitations.


Cheers,
-- 
Vinicius