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From:   "NeilBrown" <neilb@suse.de>
To:     "Chuck Lever III" <chuck.lever@oracle.com>
Cc:     "Chuck Lever" <cel@kernel.org>,
        "Linux NFS Mailing List" <linux-nfs@vger.kernel.org>,
        "Liam Howlett" <liam.howlett@oracle.com>,
        "Kees Cook" <keescook@chromium.org>,
        "Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
        "David Gow" <davidgow@google.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Andrew Morton" <akpm@linux-foundation.org>
Subject: Re: [PATCH v1 11/17] lib: add light-weight queuing mechanism.
In-reply-to: <DB109932-C918-4F1E-BAF2-92D921238D54@oracle.com>
References: <169444233785.4327.4365499966926096681.stgit@bazille.1015granger.net>,
 <169444318342.4327.18355944158180782708.stgit@bazille.1015granger.net>,
 <20230911111333.4d1a872330e924a00acb905b@linux-foundation.org>,
 <4D5C2693-40E9-467D-9F2F-59D92CBE9D3B@oracle.com>,
 <20230911140439.b273bf9e120881f038da0de7@linux-foundation.org>,
 <169447439989.19905.9386812394578844629@noble.neil.brown.name>,
 <20230911183025.5f808a70a62df79a3a1e349e@linux-foundation.org>,
 <DB109932-C918-4F1E-BAF2-92D921238D54@oracle.com>
Date:   Fri, 15 Sep 2023 11:51:54 +1000
Message-id: <169474271454.8274.2673279792882072455@noble.neil.brown.name>
Precedence: bulk

On Fri, 15 Sep 2023, Chuck Lever III wrote:
>=20
> > On Sep 11, 2023, at 9:30 PM, Andrew Morton <akpm@linux-foundation.org> wr=
ote:
> >=20
> > On Tue, 12 Sep 2023 09:19:59 +1000 "NeilBrown" <neilb@suse.de> wrote:
> >=20
> >> Plain old list_heads (which the code currently uses) require a spinlock
> >> to be taken to insert something into the queue.  As this is usually in
> >> bh context, it needs to be a spin_lock_bh().  My understanding is that
> >> the real-time developers don't much like us disabling bh.  It isn't an
> >> enormous win switching from a list_head list to a llist_node list, but
> >> there are small gains such as object size reduction and less locking.  I
> >> particularly wanted an easy-to-use library facility that could be
> >> plugged in to two different uses cases in the sunrpc code and there
> >> didn't seem to be one.  I could have written one using list_head, but
> >> llist seemed a better fix.  I think the code in sunrpc that uses this
> >> lwq looks a lot neater after the conversion.
> >=20
> > Thanks.  Could we please get words such as these into the changelog,
> > describing why it was felt necessary to add more library code?
> >=20
> > And also into the .c file, to help people who are looking at it and
> > wondering "can I use this".  And to help reviewers who are wondering
> > "could they have used Neil's thing".
>=20
> Neil, are you planning to send along a replacement for 11/17,
> or would you like me to fold the above into the patch description
> I have now?

Sorry I didn't reply sooner - been busy.
I'll send a patch that can be squashed in to 11/17 which adds some more
explanatory text.  Hopefully soonish.

NeilBrown