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=-12.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 B5704C43331 for ; Fri, 12 Mar 2021 05:29:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 99D1864FA6 for ; Fri, 12 Mar 2021 05:29:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231620AbhCLF2k (ORCPT ); Fri, 12 Mar 2021 00:28:40 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55324 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231586AbhCLF2P (ORCPT ); Fri, 12 Mar 2021 00:28:15 -0500 Received: from mail-qv1-xf33.google.com (mail-qv1-xf33.google.com [IPv6:2607:f8b0:4864:20::f33]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1AD40C061574; Thu, 11 Mar 2021 21:28:15 -0800 (PST) Received: by mail-qv1-xf33.google.com with SMTP id g8so3731554qvx.1; Thu, 11 Mar 2021 21:28:15 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=oaarikhpXaaQj6GcaKajb/NyREh5GUqd73uWAOucvZw=; b=HhkX9bKlm2Mbi362XTsvxmYPx+H11+/L5AUazrGh4nfrfUFLAKSL1dUs6V+m8hYD1e iu03Ni4GIXyuzidQERjESzBYO6S2CdXo2tB3dk5XAMAxz2yPq0XtQS7Vsoda5nNuyGqJ 9Ky2QvuZADUZluwH9E3LKrfnLqCDoQ7kj1LJxse4e188ZLpa24KkskDZhBCTBiRveOpe FcD9SQim7/0+wJce4Boa1VUY+PjA7lwQuQi3YKcCAwahM6mpD4eRtSdUbclGERH+JUGS erGKCmFku3+Z4YYg0nudJG3K1x4XvpWsLmSumcHf9JggFab3FCtwh0NCnOZrhv1H4wdM xHoA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=oaarikhpXaaQj6GcaKajb/NyREh5GUqd73uWAOucvZw=; b=glaOwC6aNw9phJZ5wpkAI5UOTlmmeuVox1A0/hr4edY1tHlJwa3aNWo/fl/uQTzoSa uugqDlUiBq4qykm9O+Vdyc5j+K0E9v2xHvaE3MRYgiFDXpTSh/2m3MrCGiRhYu87oGaL FwNmMDYOZRHdEQJm/vCMqhgiNOz+o9rf6L8eB7V6wvKR+BM3/6hOCiHPUA4hPyUyEvOU jtkUDTaWJQRRfHJ55/up4lOVp+sTfrIePeTDOed4egUtrNWzp2/rYuHuZyZfiBb5GISV k56fP9JLkja1U9XT8ygh3mjPpN4eODmdDkbhSxY+RjyypiXMLFSKgB24SLG9ks5cx4yW LRnQ== X-Gm-Message-State: AOAM533IMs8wfdtjqGPcUqBsx1nF3fzZDfDLvy15c0lyQv+glelMARV4 6WUyWXsuc08FUkWO32MaCB4= X-Google-Smtp-Source: ABdhPJzwFyPrMa5sASEXwN8SICEZ43Y7GzTMKybpYyydce66kWjt34n7EzmnZMjy1JbEW28RNyFkNA== X-Received: by 2002:a0c:b218:: with SMTP id x24mr11049374qvd.55.1615526894069; Thu, 11 Mar 2021 21:28:14 -0800 (PST) Received: from localhost ([76.73.146.210]) by smtp.gmail.com with ESMTPSA id q125sm3711558qkf.68.2021.03.11.21.28.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 11 Mar 2021 21:28:13 -0800 (PST) Date: Thu, 11 Mar 2021 21:28:12 -0800 From: Yury Norov To: Rasmus Villemoes Cc: linux-kernel@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-arch@vger.kernel.org, linux-sh@vger.kernel.org, Alexey Klimov , Andrew Morton , Andy Shevchenko , Arnd Bergmann , David Sterba , Dennis Zhou , Geert Uytterhoeven , Jianpeng Ma , Joe Perches , John Paul Adrian Glaubitz , Josh Poimboeuf , Rich Felker , Stefano Brivio , Wei Yang , Wolfram Sang , Yoshinori Sato Subject: Re: [PATCH 06/14] bitsperlong.h: introduce SMALL_CONST() macro Message-ID: <20210312052812.GB137474@yury-ThinkPad> References: <20210218040512.709186-1-yury.norov@gmail.com> <20210218040512.709186-7-yury.norov@gmail.com> <55f1e25a-3211-8247-9dd3-3777e29287db@rasmusvillemoes.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55f1e25a-3211-8247-9dd3-3777e29287db@rasmusvillemoes.dk> Precedence: bulk List-ID: X-Mailing-List: linux-sh@vger.kernel.org On Fri, Feb 19, 2021 at 12:07:27AM +0100, Rasmus Villemoes wrote: > On 18/02/2021 05.05, Yury Norov wrote: > > Many algorithms become simpler if they are passed with relatively small > > input values. One example is bitmap operations when the whole bitmap fits > > into one word. To implement such simplifications, linux/bitmap.h declares > > small_const_nbits() macro. > > > > Other subsystems may also benefit from optimizations of this sort, like > > find_bit API in the following patches. So it looks helpful to generalize > > the macro and extend it's visibility. > > Perhaps, but SMALL_CONST is too generic a name, it needs to keep "bits" > somewhere in there. So why not just keep it at small_const_nbits? > > > Signed-off-by: Yury Norov > > --- > > include/asm-generic/bitsperlong.h | 2 ++ > > include/linux/bitmap.h | 33 ++++++++++++++----------------- > > 2 files changed, 17 insertions(+), 18 deletions(-) > > > > diff --git a/include/asm-generic/bitsperlong.h b/include/asm-generic/bitsperlong.h > > index 3905c1c93dc2..0eeb77544f1d 100644 > > --- a/include/asm-generic/bitsperlong.h > > +++ b/include/asm-generic/bitsperlong.h > > @@ -23,4 +23,6 @@ > > #define BITS_PER_LONG_LONG 64 > > #endif > > > > +#define SMALL_CONST(n) (__builtin_constant_p(n) && (unsigned long)(n) < BITS_PER_LONG) > > + > > #endif /* __ASM_GENERIC_BITS_PER_LONG */ > > diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h > > index adf7bd9f0467..e89f1dace846 100644 > > --- a/include/linux/bitmap.h > > +++ b/include/linux/bitmap.h > > @@ -224,9 +224,6 @@ extern int bitmap_print_to_pagebuf(bool list, char *buf, > > * so make such users (should any ever turn up) call the out-of-line > > * versions. > > */ > > -#define small_const_nbits(nbits) \ > > - (__builtin_constant_p(nbits) && (nbits) <= BITS_PER_LONG && (nbits) > 0) > > - > > static inline void bitmap_zero(unsigned long *dst, unsigned int nbits) > > { > > unsigned int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long); > > @@ -278,7 +275,7 @@ extern void bitmap_to_arr32(u32 *buf, const unsigned long *bitmap, > > static inline int bitmap_and(unsigned long *dst, const unsigned long *src1, > > const unsigned long *src2, unsigned int nbits) > > { > > - if (small_const_nbits(nbits)) > > + if (SMALL_CONST(nbits - 1)) > > Please don't force most users to be changed to something less readable. > What's wrong with just keeping small_const_nbits() the way it is, > avoiding all this churn and keeping the readability? The wrong thing is that it's defined in include/linux/bitmap.h, and I cannot use it in include/asm-generic/bitops/find.h, so I have to either move it to a separate header, or generalize and share with find.h and other users this way. I prefer the latter option, thougt it's more verbose. > At a quick reading, one of the very few places where you end up not > passing nbits-1 but just nbits is this > > unsigned long find_next_zero_bit_le(const void *addr, unsigned > long size, unsigned long offset) > { > + if (SMALL_CONST(size)) { > + unsigned long val = *(const unsigned long *)addr; > + > + if (unlikely(offset >= size)) > + return size; > > which is a regression, for much the same reason the nbits==0 case was > excluded from small_const_nbits in the first place. If size is 0, we > used to just return 0 early in _find_next_bit. But you've introduced a > dereference of addr before that check is now done, which is > theoretically an oops. > > If find_next_zero_bit_le cannot handle nbits==BITS_PER_LONG efficiently > but requires one off-limits bit position, fine, so be it, add an extra > "small_const_nbits() && nbits < BITS_PER_LONG" (and a comment). Sure, it's my bad. I need to fix it. What would you prefer, moving the small_const_nbits() to a separate header, or introduce something like #define small_const_size(n) SMALL_CONST((n) - 1) to avoid mistakes like this? I think small_const_size() is better because it might be potentially useful for someone else, but I can go either way.