Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753216AbbHCLlO (ORCPT ); Mon, 3 Aug 2015 07:41:14 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:38012 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753150AbbHCLlL (ORCPT ); Mon, 3 Aug 2015 07:41:11 -0400 Date: Mon, 3 Aug 2015 13:41:04 +0200 From: Peter Zijlstra To: Vineet Gupta Cc: lkml , arc-linux-dev@synopsys.com Subject: Re: [PATCH 5/6] ARCv2: spinlock/rwlock/atomics: Delayed retry of failed SCOND with exponential backoff Message-ID: <20150803114104.GK25159@twins.programming.kicks-ass.net> References: <1438596188-10875-1-git-send-email-vgupta@synopsys.com> <1438596188-10875-6-git-send-email-vgupta@synopsys.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1438596188-10875-6-git-send-email-vgupta@synopsys.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3661 Lines: 115 On Mon, Aug 03, 2015 at 03:33:07PM +0530, Vineet Gupta wrote: > +#define SCOND_FAIL_RETRY_VAR_DEF \ > + unsigned int delay = 1, tmp; \ > + > +#define SCOND_FAIL_RETRY_ASM \ > + " bz 4f \n" \ > + " ; --- scond fail delay --- \n" \ > + " mov %[tmp], %[delay] \n" /* tmp = delay */ \ > + "2: brne.d %[tmp], 0, 2b \n" /* while (tmp != 0) */ \ > + " sub %[tmp], %[tmp], 1 \n" /* tmp-- */ \ > + " asl %[delay], %[delay], 1 \n" /* delay *= 2 */ \ > + " b 1b \n" /* start over */ \ > + "4: ; --- success --- \n" \ > + > +#define SCOND_FAIL_RETRY_VARS \ > + ,[delay] "+&r" (delay),[tmp] "=&r" (tmp) \ > + > +#define ATOMIC_OP(op, c_op, asm_op) \ > +static inline void atomic_##op(int i, atomic_t *v) \ > +{ \ > + unsigned int val, delay = 1, tmp; \ Maybe use your SCOND_FAIL_RETRY_VAR_DEF ? > + \ > + __asm__ __volatile__( \ > + "1: llock %[val], [%[ctr]] \n" \ > + " " #asm_op " %[val], %[val], %[i] \n" \ > + " scond %[val], [%[ctr]] \n" \ > + " \n" \ > + SCOND_FAIL_RETRY_ASM \ > + \ > + : [val] "=&r" (val) /* Early clobber to prevent reg reuse */ \ > + SCOND_FAIL_RETRY_VARS \ > + : [ctr] "r" (&v->counter), /* Not "m": llock only supports reg direct addr mode */ \ > + [i] "ir" (i) \ > + : "cc"); \ > +} \ > + > +#define ATOMIC_OP_RETURN(op, c_op, asm_op) \ > +static inline int atomic_##op##_return(int i, atomic_t *v) \ > +{ \ > + unsigned int val, delay = 1, tmp; \ Idem. > + \ > + /* \ > + * Explicit full memory barrier needed before/after as \ > + * LLOCK/SCOND thmeselves don't provide any such semantics \ > + */ \ > + smp_mb(); \ > + \ > + __asm__ __volatile__( \ > + "1: llock %[val], [%[ctr]] \n" \ > + " " #asm_op " %[val], %[val], %[i] \n" \ > + " scond %[val], [%[ctr]] \n" \ > + " \n" \ > + SCOND_FAIL_RETRY_ASM \ > + \ > + : [val] "=&r" (val) \ > + SCOND_FAIL_RETRY_VARS \ > + : [ctr] "r" (&v->counter), \ > + [i] "ir" (i) \ > + : "cc"); \ > + \ > + smp_mb(); \ > + \ > + return val; \ > +} > +#define SCOND_FAIL_RETRY_VAR_DEF \ > + unsigned int delay, tmp; \ > + > +#define SCOND_FAIL_RETRY_ASM \ > + " ; --- scond fail delay --- \n" \ > + " mov %[tmp], %[delay] \n" /* tmp = delay */ \ > + "2: brne.d %[tmp], 0, 2b \n" /* while (tmp != 0) */ \ > + " sub %[tmp], %[tmp], 1 \n" /* tmp-- */ \ > + " asl %[delay], %[delay], 1 \n" /* delay *= 2 */ \ > + " b 1b \n" /* start over */ \ > + " \n" \ > + "4: ; --- done --- \n" \ > + > +#define SCOND_FAIL_RETRY_VARS \ > + ,[delay] "=&r" (delay), [tmp] "=&r" (tmp) \ This is looking remarkably similar to the previous ones, why not a shared header? > +static inline void arch_spin_lock(arch_spinlock_t *lock) > +{ > + unsigned int val; > + SCOND_FAIL_RETRY_VAR_DEF; > + > + smp_mb(); > + > + __asm__ __volatile__( > + "0: mov %[delay], 1 \n" > + "1: llock %[val], [%[slock]] \n" > + " breq %[val], %[LOCKED], 1b \n" /* spin while LOCKED */ > + " scond %[LOCKED], [%[slock]] \n" /* acquire */ > + " bz 4f \n" /* done */ > + " \n" > + SCOND_FAIL_RETRY_ASM But,... in the case that macro is empty, the label 4 does not actually exist. I see no real reason for this to be different from the previous incarnation either. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/