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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Mon, 15 May 2023 08:56:39 -0700
Message-ID: <CAHk-=whmN7cxAgmhDBqiE=c67Q2pp2+SqCknNcj3K+QNKivaSg@mail.gmail.com>
Subject: Re: [PATCH v11 8/8] vhost: use vhost_tasks for worker threads
To:     Jens Axboe <axboe@kernel.dk>
Cc:     Christian Brauner <brauner@kernel.org>,
        Thorsten Leemhuis <linux@leemhuis.info>,
        Mike Christie <michael.christie@oracle.com>,
        nicolas.dichtel@6wind.com,
        Linux kernel regressions list <regressions@lists.linux.dev>,
        hch@infradead.org, stefanha@redhat.com, jasowang@redhat.com,
        mst@redhat.com, sgarzare@redhat.com,
        virtualization@lists.linux-foundation.org, ebiederm@xmission.com,
        konrad.wilk@oracle.com, linux-kernel@vger.kernel.org
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On Mon, May 15, 2023 at 8:52=E2=80=AFAM Jens Axboe <axboe@kernel.dk> wrote:
>
> Only potential downside is that it does make file references more
> expensive for other syscalls, since you now have a shared file table.
> But probably not something to worry about here?

Would the vhost user worker user processes ever be otherwise single-threade=
d?

I'd *assume* that a vhost user is already doing its own threads. But
maybe that's a completely bogus assumption. I don't actually use any
of this, so...

Because you are obviously 100% right that if you're otherwise
single-threaded, then a CLONE_FILES kernel helper thread will cause
the extra cost for file descriptor lookup/free due to all the race
prevention.

                 Linus