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From: Chuck Lever III <chuck.lever@oracle.com>
To: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Subject: write_space and software kTLS
Date: Mon, 14 Mar 2022 21:35:44 +0000	[thread overview]
Message-ID: <B7F08FCD-0EC1-4D7E-A560-6ADA281605AE@oracle.com> (raw)

Hey Trond-

I've made some progress getting RPC-with-TLS working in
the Linux NFS client, but I recently hit an interesting
snag and could use a little advice.

The software kTLS infrastructure uses do_tcp_sendpages()
under the covers, and that function is clearing
SOCKWQ_ASYNC_NOSPACE from under xs_nospace(). That
prevents xs_run_error_worker() from waking up xprt->sending,
stalling an RPC transport waiting for more socket write
space. I'm not sure how to address this, and I'm interested
in your opinion.

For example, why check that flag rather than just waking
up xprt->sending unconditionally?

Also just for my own understanding of how the write_space
mechanism is supposed to work for RPC, I instrumented the
code that bumps and decrements sk_write_pending, and found
that under normal workloads, the value of that field goes
negative and stays there. I'm not sure that's intended...?


--
Chuck Lever




             reply	other threads:[~2022-03-14 21:35 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-14 21:35 Chuck Lever III [this message]
2022-03-15  0:06 ` write_space and software kTLS Trond Myklebust
2022-03-15 14:01   ` Chuck Lever III

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