netdev - Re: [PATCH net-next v3 7/7] net: piggy back on the memory barrier in bql when waking queues

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Date:   Wed, 12 Apr 2023 14:06:34 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com,
        pabeni@...hat.com, alexander.duyck@...il.com, hkallweit1@...il.com,
        andrew@...n.ch, willemb@...gle.com, michael.chan@...adcom.com,
        jesse.brandeburg@...el.com, anthony.l.nguyen@...el.com
Subject: Re: [PATCH net-next v3 7/7] net: piggy back on the memory barrier in
 bql when waking queues

On Thu, Apr 06, 2023 at 05:41:40PM -0700, Jakub Kicinski wrote:
>
> I wanted to keep the same semantics as netdev_tx_completed_queue()
> which only barriers if (bytes). Not in the least to make it obvious
> to someone looking at the code of netdev_txq_completed_mb() (and not
> the comment above it) that it doesn't _always_ put a barrier in.

OK, but I think we should instead change netdev_tx_compelted_queue
to do the smp_mb unconditionally.  We should never optimise for the
unlikely case, and it is extremely unlikely for a TX cleanup routine
to wind up with nothing to do.

Thanks,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt