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 C5290C433E9 for ; Fri, 12 Mar 2021 21:54:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A090664D9F for ; Fri, 12 Mar 2021 21:54:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235458AbhCLVxm (ORCPT ); Fri, 12 Mar 2021 16:53:42 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42450 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235488AbhCLVxi (ORCPT ); Fri, 12 Mar 2021 16:53:38 -0500 Received: from mail-qk1-x734.google.com (mail-qk1-x734.google.com [IPv6:2607:f8b0:4864:20::734]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5840AC061574; Fri, 12 Mar 2021 13:53:38 -0800 (PST) Received: by mail-qk1-x734.google.com with SMTP id d20so25968370qkc.2; Fri, 12 Mar 2021 13:53:38 -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=9Ef5EY2WMrKCR6YQJjvJccCPLCTaOpepUxDNfS7WTGo=; b=tjjBW8j2bo/jen8nkSMnG+TdHfhLmzrUK7o1rk3vK96G0IpIxYfAwtS4Wtq1p3NUWg WbZy4AB7w0vnRvtXc5mbl+/aY9FUBRS94KHCWupN3J6saDc3KnMEvsKcJRPPdhFypfYj ZZHTLijqqGENsbuC356dpSkGNcySYXCcKLMyPqsNcTORKfpXvohtdsIT+UBXeA3JyGrD 0KJ5xP4c2oPFv6rWr3osEdndh860EXuZ3FU/t/p+Hy+Cp2AkYNP2fFHKgkvCi1mHwhCd 57LJ66TvNRjJuGyTrcZH1XKT/5piUQPPT+zCNujfJ2e9/SISYPTv9jt59NXJdejKi/oh jUPg== 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=9Ef5EY2WMrKCR6YQJjvJccCPLCTaOpepUxDNfS7WTGo=; b=ixMvB4XbjAoSOQWbCokZ8GtgM1eULI6A4sENMZVzmgmzVupfSUp4mQG479GzC3kyMH lT35vFh8nPf4RmaMigXvT0+wbD6cb0UsnjfpxFXtBsbqzvXKG3YRRCGjAhwvwyv5eCqk UOHsfqk3putof8fNQjJBpRW15ycbNlt09R2U6onhfH0bI72CbdOpD3ODLohEx+XYmxcE n7hGJwVXu99pUFuBr5urpetgOypmiDGlY8QXL1OoRfr6N00EVBt2fHf8LowlMBCDFg4v 3JeOSCshfd07TWPhLxwHbqO4sFmRw9laQ3I/Eq34WyWgI4aDjbG7JTbOS+Z57twngwTx bdEQ== X-Gm-Message-State: AOAM533p0RDGJlNZPl7rPdYrDOzteFFyUpjpX50qUL6Y5vmL6G5a/UDE HpwxcbdijbFzwmNEcc4c/MM= X-Google-Smtp-Source: ABdhPJyB61QmOAM1xkM7zp9iyyydvZwe9L+k8hjEI9bjJ/F+iikmGnqQCe8EI+Cnk01d/LQ/tIOHfg== X-Received: by 2002:a37:9b01:: with SMTP id d1mr12132300qke.337.1615586017485; Fri, 12 Mar 2021 13:53:37 -0800 (PST) Received: from localhost ([76.73.146.210]) by smtp.gmail.com with ESMTPSA id 66sm5319791qkk.18.2021.03.12.13.53.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 12 Mar 2021 13:53:37 -0800 (PST) Date: Fri, 12 Mar 2021 13:53:36 -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: <20210312215336.GA249694@yury-ThinkPad> References: <20210218040512.709186-1-yury.norov@gmail.com> <20210218040512.709186-7-yury.norov@gmail.com> <55f1e25a-3211-8247-9dd3-3777e29287db@rasmusvillemoes.dk> <20210312052812.GB137474@yury-ThinkPad> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 12, 2021 at 10:12:22AM +0100, Rasmus Villemoes wrote: > On 12/03/2021 06.28, Yury Norov wrote: > > 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. > > The logical place would be the same place the BITS_PER_LONG macro is > defined, no? Yes. This where I placed SMALL_CONST() in current version. > No need to introduce a new header for that, and all current > users of small_const_nbits() must already (very possibly indirectly) > include asm-generic/bitsperlong.h. > > I do prefer to keep both the name small_const_nbits() and its current > semantics, which, although not currently spelled out that way anywhere, > is "is BITMAP_SIZE(nbits) known at compile time and equal to 1", which > is precisely what allows the static inlines to unconditionally > dereference the pointer (that's the "exclude the 0 case") and just deal > with that one word. > > I don't like either SMALL_CONST or small_const_size, because nothing in > there says it has anything to do with bit ops. As I said, if you have > some special place that for some reason cannot handle > nbits==BITS_PER_LONG, then just add that as an additional constraint > with a comment why. OK, I'll move small_const_nbits() to the bitsperlong header and resubmit shortly. My concern still is that nbits is too specific for bitsperlong.h, but if you're good with it, I'm OK as well.