linux-kernel - Re: [PATCH] nvme/tcp: handle tls partially sent records in write

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Message-ID: <143591bfd3499f2ee90034190a94154a965f563d.camel@gmail.com>
Date: Wed, 08 Oct 2025 12:11:52 +1000
From: Wilfred Mallawa <wilfred.opensource@...il.com>
To: Hannes Reinecke <hare@...e.de>, linux-nvme@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Cc: Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...nel.dk>, Christoph
 Hellwig <hch@....de>, Sagi Grimberg <sagi@...mberg.me>, John Fastabend
 <john.fastabend@...il.com>,  Jakub Kicinski	 <kuba@...nel.org>, Sabrina
 Dubroca <sd@...asysnail.net>, "David S . Miller"	 <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Paolo Abeni	 <pabeni@...hat.com>, Simon
 Horman <horms@...nel.org>
Subject: Re: [PATCH] nvme/tcp: handle tls partially sent records in
 write_space()

On Tue, 2025-10-07 at 11:51 +0200, Hannes Reinecke wrote:
> On 10/7/25 11:24, Wilfred Mallawa wrote:
> > On Tue, 2025-10-07 at 07:19 +0200, Hannes Reinecke wrote:
> > > On 10/7/25 02:46, Wilfred Mallawa wrote:
> > > > From: Wilfred Mallawa <wilfred.mallawa@....com>
> > > > 
> > > 
> > [...]
> > > I wonder: Do we really need to check for a partially assembled
> > > record,
> > > or wouldn't it be easier to call queue->write_space() every time
> > > here?
> > > We sure would end up with executing the callback more often, but
> > > if
> > > no
> > > data is present it shouldn't do any harm.
> > > 
> > > IE just use
> > > 
> > > if (nvme_tcp_queue_tls(queue)
> > >       queue->write_space(sk);
> > 
> > Hey Hannes,
> > 
> > This was my initial approach, but I figured using
> > tls_is_partially_sent_record() might be slightly more efficient.
> > But if
> > we think that's negligible, happy to go with this approach
> > (omitting
> > the partial record check).
> > 
> Please do.
> Performance testing on NVMe-TCP is notoriously tricky, so for now we
> really should not assume anything here.
> And it's making the patch _vastly_ simpler, _and_ we don't have to
> involve the networking folks here.

Okay, will send a V2 with this approach.

> We have a similar patch for the data_ready() function in nvmet_tcp(),
> and that seemed to work, too.
> Nit: we don't unset the 'NOSPACE' flag there. Can you check if that's
> really required? 
> And, if it is, fixup nvmet_tcp() to unset it?
> Or, if not, modify your patch to not clear it?

I don't see why we would need to clear the NOSPACE flag in
data_ready()? My understanding is that this flag is used when the send
buffer is full.

I would think the clear_bit() is necessary in write_space() since it
would typically get done in something like sk_stream_write_space()? 
However, running some quick FIOs with the clear_bit() removed, things
seem to work. Not sure if removing it has any further implications
though...

Regards,
Wilfred


> Cheers,
> 
> Hannes