Re: [PATCH 0/5] Generic Ticket Spinlocks

From: Arnd Bergmann <arnd@arndb.de>
To: Palmer Dabbelt <palmer@rivosinc.com>
Cc: linux-riscv <linux-riscv@lists.infradead.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Jonas Bonn <jonas@southpole.se>,
	Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>,
	Stafford Horne <shorne@gmail.com>, Ingo Molnar <mingo@redhat.com>,
	Will Deacon <will@kernel.org>, Waiman Long <longman@redhat.com>,
	Boqun Feng <boqun.feng@gmail.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>, Arnd Bergmann <arnd@arndb.de>,
	Jisheng Zhang <jszhang@kernel.org>,
	Kefeng Wang <wangkefeng.wang@huawei.com>,
	Openrisc <openrisc@lists.librecores.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>
Subject: Re: [PATCH 0/5] Generic Ticket Spinlocks
Date: Thu, 17 Mar 2022 10:16:50 +0100	[thread overview]
Message-ID: <CAK8P3a0J3ViDWserQew2wt95Hnu6AHT5gmSxtUz0x5W2fWdxBA@mail.gmail.com> (raw)
In-Reply-To: <20220316232600.20419-1-palmer@rivosinc.com>

On Thu, Mar 17, 2022 at 12:25 AM Palmer Dabbelt <palmer@rivosinc.com> wrote:
>
> Peter sent an RFC out about a year ago
> <https://lore.kernel.org/lkml/YHbBBuVFNnI4kjj3@hirez.programming.kicks-ass.net/>,
> but after a spirited discussion it looks like we lost track of things.
> IIRC there was broad consensus on this being the way to go, but there
> was a lot of discussion so I wasn't sure.  Given that it's been a year,
> I figured it'd be best to just send this out again formatted a bit more
> explicitly as a patch.
>
> This has had almost no testing (just a build test on RISC-V defconfig),
> but I wanted to send it out largely as-is because I didn't have a SOB
> from Peter on the code.  I had sent around something sort of similar in
> spirit, but this looks completely re-written.  Just to play it safe I
> wanted to send out almost exactly as it was posted.  I'd probably rename
> this tspinlock and tspinlock_types, as the mis-match kind of makes my
> eyes go funny, but I don't really care that much.  I'll also go through
> the other ports and see if there's any more candidates, I seem to
> remember there having been more than just OpenRISC but it's been a
> while.
>
> I'm in no big rush for this and given the complex HW dependencies I
> think it's best to target it for 5.19, that'd give us a full merge
> window for folks to test/benchmark it on their systems to make sure it's
> OK.  RISC-V has a forward progress guarantee so we should be safe, but
> these can always trip things up.

This all looks good to me, feel free to merge the asm-generic
bits through the riscv tree.

Regarding the naming, my preference would be to just use
this version in place of the (currently useless) asm-generic/spinlock.h,
and just naming it arch_spin_lock() etc.

This way, converting an architecture to the generic ticket lock can
be done simply by removing its custom asm/spinlock.h. Or it
could stay with the current name, but then have a new
asm-generic/spinlock.h that just includes both asm/ticket_lock.h
and asm/qrwlock.h.

      Arnd