From mboxrd@z Thu Jan 1 00:00:00 1970 From: Waiman Long Date: Thu, 17 Mar 2022 11:03:40 -0400 Subject: [OpenRISC] [PATCH 2/5] asm-generic: ticket-lock: New generic ticket-based spinlock In-Reply-To: References: <20220316232600.20419-1-palmer@rivosinc.com> <20220316232600.20419-3-palmer@rivosinc.com> Message-ID: <364c72a9-64ca-592a-510b-d48a963121aa@redhat.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: openrisc@lists.librecores.org On 3/17/22 09:57, Boqun Feng wrote: > On Wed, Mar 16, 2022 at 04:25:57PM -0700, Palmer Dabbelt wrote: >> From: Peter Zijlstra >> >> This is a simple, fair spinlock. Specifically it doesn't have all the >> subtle memory model dependencies that qspinlock has, which makes it more >> suitable for simple systems as it is more likely to be correct. >> >> [Palmer: commit text] >> Signed-off-by: Palmer Dabbelt >> >> -- >> >> I have specifically not included Peter's SOB on this, as he sent his >> original patch >> >> without one. >> --- >> include/asm-generic/ticket-lock-types.h | 11 ++++ >> include/asm-generic/ticket-lock.h | 86 +++++++++++++++++++++++++ >> 2 files changed, 97 insertions(+) >> create mode 100644 include/asm-generic/ticket-lock-types.h >> create mode 100644 include/asm-generic/ticket-lock.h >> >> diff --git a/include/asm-generic/ticket-lock-types.h b/include/asm-generic/ticket-lock-types.h >> new file mode 100644 >> index 000000000000..829759aedda8 >> --- /dev/null >> +++ b/include/asm-generic/ticket-lock-types.h >> @@ -0,0 +1,11 @@ >> +/* SPDX-License-Identifier: GPL-2.0 */ >> + >> +#ifndef __ASM_GENERIC_TICKET_LOCK_TYPES_H >> +#define __ASM_GENERIC_TICKET_LOCK_TYPES_H >> + >> +#include >> +typedef atomic_t arch_spinlock_t; >> + >> +#define __ARCH_SPIN_LOCK_UNLOCKED ATOMIC_INIT(0) >> + >> +#endif /* __ASM_GENERIC_TICKET_LOCK_TYPES_H */ >> diff --git a/include/asm-generic/ticket-lock.h b/include/asm-generic/ticket-lock.h >> new file mode 100644 >> index 000000000000..3f0d53e21a37 >> --- /dev/null >> +++ b/include/asm-generic/ticket-lock.h >> @@ -0,0 +1,86 @@ >> +/* SPDX-License-Identifier: GPL-2.0 */ >> + >> +/* >> + * 'Generic' ticket-lock implementation. >> + * >> + * It relies on atomic_fetch_add() having well defined forward progress >> + * guarantees under contention. If your architecture cannot provide this, stick >> + * to a test-and-set lock. >> + * >> + * It also relies on atomic_fetch_add() being safe vs smp_store_release() on a >> + * sub-word of the value. This is generally true for anything LL/SC although >> + * you'd be hard pressed to find anything useful in architecture specifications >> + * about this. If your architecture cannot do this you might be better off with >> + * a test-and-set. >> + * >> + * It further assumes atomic_*_release() + atomic_*_acquire() is RCpc and hence >> + * uses atomic_fetch_add() which is SC to create an RCsc lock. >> + * > Probably it's better to use "fully-ordered" instead of "SC", because our > atomic documents never use "SC" or "Sequential Consisteny" to describe > the semantics, further I'm not sure our "fully-ordered" is equivalent to > SC, better not cause misunderstanding in the future here. The terms RCpc, RCsc comes from academia. I believe we can keep this but add more comment to elaborate what they are and what do they mean for the average kernel engineer. Cheers, Longman