From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 62D19C43387 for ; Mon, 14 Jan 2019 19:00:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3117120659 for ; Mon, 14 Jan 2019 19:00:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726777AbfANTAd (ORCPT ); Mon, 14 Jan 2019 14:00:33 -0500 Received: from foss.arm.com ([217.140.101.70]:39054 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726643AbfANTAd (ORCPT ); Mon, 14 Jan 2019 14:00:33 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 5D07480D; Mon, 14 Jan 2019 11:00:32 -0800 (PST) Received: from fuggles.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8F0243F5BD; Mon, 14 Jan 2019 11:00:30 -0800 (PST) Date: Mon, 14 Jan 2019 19:00:25 +0000 From: Will Deacon To: Vineet Gupta Cc: linux-kernel@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-mm@kvack.org, peterz@infradead.org, Miklos Szeredi , Ingo Molnar , Jani Nikula , Chris Wilson , Andrew Morton Subject: Re: [PATCH 3/3] bitops.h: set_mask_bits() to return old value Message-ID: <20190114190025.GA29167@fuggles.cambridge.arm.com> References: <1547166387-19785-1-git-send-email-vgupta@synopsys.com> <1547166387-19785-4-git-send-email-vgupta@synopsys.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1547166387-19785-4-git-send-email-vgupta@synopsys.com> User-Agent: Mutt/1.11.1+86 (6f28e57d73f2) () Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 10, 2019 at 04:26:27PM -0800, Vineet Gupta wrote: > | > Also, set_mask_bits is used in fs quite a bit and we can possibly come up > | > with a generic llsc based implementation (w/o the cmpxchg loop) > | > | May I also suggest changing the return value of set_mask_bits() to old. > | > | You can compute the new value given old, but you cannot compute the old > | value given new, therefore old is the better return value. Also, no > | current user seems to use the return value, so changing it is without > | risk. > > Link: http://lkml.kernel.org/g/20150807110955.GH16853@twins.programming.kicks-ass.net > Suggested-by: Peter Zijlstra > Cc: Miklos Szeredi > Cc: Ingo Molnar > Cc: Jani Nikula > Cc: Chris Wilson > Cc: Andrew Morton > Cc: Will Deacon > Signed-off-by: Vineet Gupta > --- > include/linux/bitops.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/bitops.h b/include/linux/bitops.h > index 705f7c442691..602af23b98c7 100644 > --- a/include/linux/bitops.h > +++ b/include/linux/bitops.h > @@ -246,7 +246,7 @@ static __always_inline void __assign_bit(long nr, volatile unsigned long *addr, > new__ = (old__ & ~mask__) | bits__; \ > } while (cmpxchg(ptr, old__, new__) != old__); \ > \ > - new__; \ > + old__; \ > }) > #endif Acked-by: Will Deacon May also explain why no in-tree users appear to use the return value! Will From mboxrd@z Thu Jan 1 00:00:00 1970 From: will.deacon@arm.com (Will Deacon) Date: Mon, 14 Jan 2019 19:00:25 +0000 Subject: [PATCH 3/3] bitops.h: set_mask_bits() to return old value In-Reply-To: <1547166387-19785-4-git-send-email-vgupta@synopsys.com> References: <1547166387-19785-1-git-send-email-vgupta@synopsys.com> <1547166387-19785-4-git-send-email-vgupta@synopsys.com> List-ID: Message-ID: <20190114190025.GA29167@fuggles.cambridge.arm.com> To: linux-snps-arc@lists.infradead.org On Thu, Jan 10, 2019@04:26:27PM -0800, Vineet Gupta wrote: > | > Also, set_mask_bits is used in fs quite a bit and we can possibly come up > | > with a generic llsc based implementation (w/o the cmpxchg loop) > | > | May I also suggest changing the return value of set_mask_bits() to old. > | > | You can compute the new value given old, but you cannot compute the old > | value given new, therefore old is the better return value. Also, no > | current user seems to use the return value, so changing it is without > | risk. > > Link: http://lkml.kernel.org/g/20150807110955.GH16853 at twins.programming.kicks-ass.net > Suggested-by: Peter Zijlstra > Cc: Miklos Szeredi > Cc: Ingo Molnar > Cc: Jani Nikula > Cc: Chris Wilson > Cc: Andrew Morton > Cc: Will Deacon > Signed-off-by: Vineet Gupta > --- > include/linux/bitops.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/bitops.h b/include/linux/bitops.h > index 705f7c442691..602af23b98c7 100644 > --- a/include/linux/bitops.h > +++ b/include/linux/bitops.h > @@ -246,7 +246,7 @@ static __always_inline void __assign_bit(long nr, volatile unsigned long *addr, > new__ = (old__ & ~mask__) | bits__; \ > } while (cmpxchg(ptr, old__, new__) != old__); \ > \ > - new__; \ > + old__; \ > }) > #endif Acked-by: Will Deacon May also explain why no in-tree users appear to use the return value! Will