Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752668AbbK3GRx (ORCPT ); Mon, 30 Nov 2015 01:17:53 -0500 Received: from mail-wm0-f52.google.com ([74.125.82.52]:34237 "EHLO mail-wm0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750917AbbK3GRu (ORCPT ); Mon, 30 Nov 2015 01:17:50 -0500 MIME-Version: 1.0 In-Reply-To: References: <563B8E85.6090104@hpe.com> <563CE5A6.8080409@hpe.com> <56560691.8000702@hpe.com> Date: Mon, 30 Nov 2015 14:17:49 +0800 Message-ID: Subject: Re: Improve spinlock performance by moving work to one core From: Ling Ma To: Waiman Long Cc: Peter Zijlstra , mingo@redhat.com, linux-kernel@vger.kernel.org, Ling Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3360 Lines: 99 Any comments, the patch is acceptable ? Thanks Ling 2015-11-26 17:00 GMT+08:00 Ling Ma : > Run thread.c with clean kernel 4.3.0-rc4, perf top -G also indicates > cache_flusharray and cache_alloc_refill functions spend 25.6% time > on queued_spin_lock_slowpath totally. it means the compared data > from our spinlock-test.patch is reliable. > > Thanks > Ling > > 2015-11-26 11:49 GMT+08:00 Ling Ma : >> Hi Longman, >> >> All compared data is from the below operation in spinlock-test.patch: >> >> +#if ORG_QUEUED_SPINLOCK >> + org_queued_spin_lock((struct qspinlock *)&pa.n->list_lock); >> + refill_fn(&pa); >> + org_queued_spin_unlock((struct qspinlock *)&pa.n->list_lock); >> +#else >> + new_spin_lock((struct nspinlock *)&pa.n->list_lock, refill_fn, &pa); >> +#endif >> >> and >> >> +#if ORG_QUEUED_SPINLOCK >> + org_queued_spin_lock((struct qspinlock *)&pa.n->list_lock); >> + flusharray_fn(&pa); >> + org_queued_spin_unlock((struct qspinlock *)&pa.n->list_lock); >> +#else >> + new_spin_lock((struct nspinlock *)&pa.n->list_lock, flusharray_fn, &pa); >> +#endif >> >> So the result is correct and fair. >> >> Yes, we updated the code in include/asm-generic/qspinlock.h to >> simplified modification and avoid kernel crash, >> for example there are 10 lock scenarios to use new spin lock, >> because bottle-neck is only from one or two scenarios, we only modify them, >> other lock scenarios will continue to use the lock in qspinlock.h, we >> must modify the code, >> otherwise the operation will be hooked in the queued and never be waken up. >> >> Thanks >> Ling >> >> >> >> 2015-11-26 3:05 GMT+08:00 Waiman Long : >>> On 11/23/2015 04:41 AM, Ling Ma wrote: >>>> Hi Longman, >>>> >>>> Attachments include user space application thread.c and kernel patch >>>> spinlock-test.patch based on kernel 4.3.0-rc4 >>>> >>>> we run thread.c with kernel patch, test original and new spinlock respectively, >>>> perf top -G indicates thread.c cause cache_alloc_refill and >>>> cache_flusharray functions to spend ~25% time on original spinlock, >>>> after introducing new spinlock in two functions, the cost time become ~22%. >>>> >>>> The printed data also tell us the new spinlock improves performance >>>> by about 15%( 93841765576 / 81036259588) on E5-2699V3 >>>> >>>> Appreciate your comments. >>>> >>>> >>> >>> I saw that you make the following changes in the code: >>> >>> static __always_inline void queued_spin_lock(struct qspinlock *lock) >>> { >>> u32 val; >>> - >>> +repeat: >>> val = atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL); >>> if (likely(val == 0)) >>> return; >>> - queued_spin_lock_slowpath(lock, val); >>> + goto repeat; >>> + //queued_spin_lock_slowpath(lock, val); >>> } >>> >>> >>> This effectively changes the queued spinlock into an unfair byte lock. >>> Without a pause to moderate the cmpxchg() call, that is especially bad >>> for performance. Is the performance data above refers to the unfair byte >>> lock versus your new spinlock? >>> >>> Cheers, >>> Longman -- 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/