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Re: [PATCH 1/1] nbd/server: push pending frames after sending reply

From: Kevin Wolf
Subject: Re: [PATCH 1/1] nbd/server: push pending frames after sending reply
Date: Mon, 27 Mar 2023 13:44:59 +0200

Am 24.03.2023 um 11:47 hat Florian Westphal geschrieben:
> qemu-nbd doesn't set TCP_NODELAY on the tcp socket.
> Kernel waits for more data and avoids transmission of small packets.
> Without TLS this is barely noticeable, but with TLS this really shows.
> Booting a VM via qemu-nbd on localhost (with tls) takes more than
> 2 minutes on my system.  tcpdump shows frequent wait periods, where no
> packets get sent for a 40ms period.
> Add explicit (un)corking when processing (and responding to) requests.
> "TCP_CORK, &zero" after earlier "CORK, &one" will flush pending data.
> VM Boot time:
> main:    no tls:  23s, with tls: 2m45s
> patched: no tls:  14s, with tls: 15s
> VM Boot time, qemu-nbd via network (same lan):
> main:    no tls:  18s, with tls: 1m50s
> patched: no tls:  17s, with tls: 18s
> Future optimization: if we could detect if there is another pending
> request we could defer the uncork operation because more data would be
> appended.
> Signed-off-by: Florian Westphal <fw@strlen.de>

Thanks, applied to the block branch.


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