From: Peter Zijlstra <peterz@infradead.org>
To: Guo Ren <ren_guo@c-sky.com>
Cc: linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
tglx@linutronix.de, daniel.lezcano@linaro.org,
jason@lakedaemon.net, arnd@arndb.de,
c-sky_gcc_upstream@c-sky.com, gnu-csky@mentor.com,
thomas.petazzoni@bootlin.com, wbx@uclibc-ng.org,
green.hu@gmail.com
Subject: Re: [PATCH V2 11/19] csky: Atomic operations
Date: Thu, 5 Jul 2018 19:59:02 +0200 [thread overview]
Message-ID: <20180705175902.GF2530@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <860b8db036b33d7b3648cb1f4ec827a53dc1a01b.1530465326.git.ren_guo@c-sky.com>
On Mon, Jul 02, 2018 at 01:30:14AM +0800, Guo Ren wrote:
> +static inline void arch_spin_lock(arch_spinlock_t *lock)
> +{
> + unsigned int *p = &lock->lock;
> + unsigned int tmp;
> +
> + asm volatile (
> + "1: ldex.w %0, (%1) \n"
> + " bnez %0, 1b \n"
> + " movi %0, 1 \n"
> + " stex.w %0, (%1) \n"
> + " bez %0, 1b \n"
> + : "=&r" (tmp)
> + : "r"(p)
> + : "memory");
> + smp_mb();
> +}
Test-and-set with MB acting as ACQUIRE, ok.
> +static inline void arch_spin_unlock(arch_spinlock_t *lock)
> +{
> + unsigned int *p = &lock->lock;
> + unsigned int tmp;
> +
> + smp_mb();
> + asm volatile (
> + "1: ldex.w %0, (%1) \n"
> + " movi %0, 0 \n"
> + " stex.w %0, (%1) \n"
> + " bez %0, 1b \n"
> + : "=&r" (tmp)
> + : "r"(p)
> + : "memory");
> +}
MB acting for RELEASE, but _why_ are you using a LDEX/STEX to clear the
lock word? Would not a normal store work?
Also, the fact that you need MB for release implies your LDEX does not
in fact imply anything and your xchg/cmpxchg implementation is broken.
> +static inline int arch_spin_trylock(arch_spinlock_t *lock)
> +{
> + unsigned int *p = &lock->lock;
> + unsigned int tmp;
> +
> + asm volatile (
> + "1: ldex.w %0, (%1) \n"
> + " bnez %0, 2f \n"
> + " movi %0, 1 \n"
> + " stex.w %0, (%1) \n"
> + " bez %0, 1b \n"
> + " movi %0, 0 \n"
> + "2: \n"
> + : "=&r" (tmp)
> + : "r"(p)
> + : "memory");
> + smp_mb();
> +
> + return !tmp;
> +}
Strictly speaking you can avoid the MB on failure. You only need to
provide ACQUIRE semantics on success.
That said, I would really suggest you implement a ticket lock instead of
a test-and-set lock. They're not really all that complicated and do
provide better worst case behaviour.
> +/****** read lock/unlock/trylock ******/
Please have a look at using qrwlock -- esp. if you implement a ticket
lock, then the rwlock comes for 'free'.
next prev parent reply other threads:[~2018-07-05 17:59 UTC|newest]
Thread overview: 87+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-01 17:30 [PATCH V2 00/19] C-SKY(csky) Linux Kernel Port Guo Ren
2018-07-01 17:30 ` [PATCH V2 01/19] csky: Build infrastructure Guo Ren
2018-07-01 21:01 ` Randy Dunlap
2018-07-02 1:13 ` Guo Ren
2018-07-03 3:33 ` Rob Herring
2018-07-03 9:14 ` Guo Ren
2018-07-03 16:03 ` Arnd Bergmann
2018-07-04 11:40 ` Guo Ren
2018-07-01 17:30 ` [PATCH V2 02/19] csky: defconfig Guo Ren
2018-07-03 3:16 ` Rob Herring
2018-07-03 8:31 ` Guo Ren
2018-07-01 17:30 ` [PATCH V2 03/19] csky: Kernel booting Guo Ren
2018-07-01 17:30 ` [PATCH V2 04/19] csky: Exception handling Guo Ren
2018-07-01 17:30 ` [PATCH V2 05/19] csky: System Call Guo Ren
2018-07-03 19:53 ` Arnd Bergmann
2018-07-04 11:49 ` Guo Ren
2018-07-04 21:04 ` Arnd Bergmann
2018-07-05 5:38 ` Guo Ren
2018-07-01 17:30 ` [PATCH V2 06/19] csky: Cache and TLB routines Guo Ren
2018-07-05 17:40 ` Peter Zijlstra
2018-07-07 11:51 ` Guo Ren
2018-07-01 17:30 ` [PATCH V2 07/19] csky: MMU and page table management Guo Ren
2018-07-02 13:29 ` Christoph Hellwig
2018-07-03 2:53 ` Guo Ren
2018-07-01 17:30 ` [PATCH V2 08/19] csky: Process management and Signal Guo Ren
2018-07-01 17:30 ` [PATCH V2 09/19] csky: VDSO and rt_sigreturn Guo Ren
2018-07-01 17:30 ` [PATCH V2 10/19] csky: IRQ handling Guo Ren
2018-07-01 17:30 ` [PATCH V2 11/19] csky: Atomic operations Guo Ren
2018-07-05 17:50 ` Peter Zijlstra
2018-07-06 11:01 ` Guo Ren
2018-07-06 11:56 ` Peter Zijlstra
2018-07-06 12:17 ` Peter Zijlstra
2018-07-07 8:08 ` Guo Ren
2018-07-07 20:10 ` Andrea Parri
2018-07-08 1:05 ` Guo Ren
2018-07-07 7:42 ` Guo Ren
2018-07-07 19:54 ` Andrea Parri
2018-07-08 0:39 ` Guo Ren
2018-07-05 17:59 ` Peter Zijlstra [this message]
2018-07-06 11:44 ` Guo Ren
2018-07-06 12:03 ` Peter Zijlstra
2018-07-06 13:01 ` Peter Zijlstra
2018-07-06 14:06 ` Guo Ren
2018-07-05 18:00 ` Peter Zijlstra
2018-07-06 11:48 ` Guo Ren
2018-07-06 12:05 ` Peter Zijlstra
2018-07-06 13:46 ` Guo Ren
2018-07-01 17:30 ` [PATCH V2 12/19] csky: ELF and module probe Guo Ren
2018-07-01 17:30 ` [PATCH V2 13/19] csky: Library functions Guo Ren
2018-07-03 20:04 ` Arnd Bergmann
2018-07-04 10:51 ` Guo Ren
2018-07-01 17:30 ` [PATCH V2 14/19] csky: User access Guo Ren
2018-07-01 17:30 ` [PATCH V2 15/19] csky: Debug and Ptrace GDB Guo Ren
2018-07-01 17:30 ` [PATCH V2 16/19] csky: SMP support Guo Ren
2018-07-05 18:05 ` Peter Zijlstra
2018-07-06 6:07 ` Guo Ren
2018-07-06 9:39 ` Peter Zijlstra
2018-07-06 13:22 ` Guo Ren
2018-07-06 5:24 ` Mark Rutland
2018-07-06 11:32 ` Guo Ren
2018-07-06 11:43 ` Mark Rutland
2018-07-06 12:26 ` Guo Ren
2018-07-06 16:21 ` Mark Rutland
2018-07-07 6:16 ` Guo Ren
2018-07-01 17:30 ` [PATCH V2 17/19] csky: Misc headers Guo Ren
2018-07-01 17:30 ` [PATCH V2 18/19] clocksource: add C-SKY clocksource drivers Guo Ren
2018-07-01 17:34 ` Guo Ren
2018-07-03 9:39 ` Thomas Gleixner
2018-07-04 10:49 ` Guo Ren
2018-07-04 14:35 ` Thomas Gleixner
2018-07-05 5:03 ` Guo Ren
2018-07-04 17:05 ` Daniel Lezcano
2018-07-05 3:30 ` Guo Ren
2018-07-05 9:23 ` Daniel Lezcano
2018-07-06 5:57 ` Guo Ren
2018-07-01 17:30 ` [PATCH V2 19/19] irqchip: add C-SKY irqchip drivers Guo Ren
2018-07-03 3:27 ` Rob Herring
2018-07-03 7:38 ` Guo Ren
2018-07-03 9:28 ` Thomas Gleixner
2018-07-04 5:08 ` Guo Ren
2018-07-04 6:43 ` Thomas Gleixner
2018-07-04 11:58 ` Guo Ren
2018-07-11 9:51 ` [PATCH V2 00/19] C-SKY(csky) Linux Kernel Port David Howells
2018-07-12 12:51 ` Guo Ren
2018-07-12 16:04 ` Sandra Loosemore
2018-07-13 1:30 ` Guo Ren
2018-07-13 10:23 ` David Howells
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