Re: [PATCH] tcp, tcp_splice: Don't set SO_SNDBUF and SO_RCVBUF to maximum values

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Feb 13, 2025 at 11:16:50PM +0100, Stefano Brivio wrote:
> I added this a long long time ago because it dramatically improved
> throughput back then: with rmem_max and wmem_max >= 4 MiB, we would
> force send and receive buffer sizes for TCP sockets to the maximum
> allowed value.
> 
> This effectively disables TCP auto-tuning, which would otherwise allow
> us to exceed those limits, as crazy as it might sound. But in any
> case, it made sense.
> 
> Now that we have zero (internal) copies on every path, plus vhost-user
> support, it turns out that these settings are entirely obsolete. I get
> substantially the same throughput in every test we perform, even with
> very short durations (one second).
> 
> The settings are not just useless: they actually cause us quite some
> trouble on guest state migration, because they lead to huge queues
> that need to be moved as well.
> 
> Drop those settings.
> 
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Hooray!

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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