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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E174DC54EE9 for ; Mon, 19 Sep 2022 13:46:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230177AbiISNqS (ORCPT ); Mon, 19 Sep 2022 09:46:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55286 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229611AbiISNqQ (ORCPT ); Mon, 19 Sep 2022 09:46:16 -0400 Received: from mga17.intel.com (mga17.intel.com [192.55.52.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 146FB303ED for ; Mon, 19 Sep 2022 06:46:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1663595165; x=1695131165; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=XxfXVawkIpRkw9Sta27sG26kldmJgVeo7UfKSRubE1M=; b=T3hP3hvg1kJzPt1LlBXMSBm8xkM9G+VyTBTogOwlSCKYjoAJ5V37UQDJ IZVZ7LQDT3cLk3dENUYPFWq1MDbsuVqhLz+PntFf0uLu/wdSU+yX2OwBd d0gEZHsOZ+0JJtAinzJWpUxE8BZBPCgoQLkBHhRUQPVduxbyXTF9K5cfC k5ufiUGIKp2kRZxNjj6KR42aQcxglw/uAm5WV9ttzLAxaNOc6gNdO5RSj VYXxmH2lFG1D41XyHzDhOsihLDCtg+lKQjNl2eArh+Ekar4+cLqP6cquM 6tpgTBlumkSFagWd19fLVGDANJBmuZMBAnWY5FyQT9MGXB/nZrNOA2V3e w==; X-IronPort-AV: E=McAfee;i="6500,9779,10475"; a="279784133" X-IronPort-AV: E=Sophos;i="5.93,327,1654585200"; d="scan'208";a="279784133" Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Sep 2022 06:46:00 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.93,327,1654585200"; d="scan'208";a="722303636" Received: from smile.fi.intel.com ([10.237.72.54]) by fmsmga002.fm.intel.com with ESMTP; 19 Sep 2022 06:45:56 -0700 Received: from andy by smile.fi.intel.com with local (Exim 4.96) (envelope-from ) id 1oaH5u-004ZcK-1U; Mon, 19 Sep 2022 16:45:54 +0300 Date: Mon, 19 Sep 2022 16:45:54 +0300 From: Andy Shevchenko To: Yury Norov Cc: Linus Torvalds , linux-kernel@vger.kernel.org, Alexey Klimov , Andy Whitcroft , Catalin Marinas , David Laight , Dennis Zhou , Guenter Roeck , Kees Cook , Rasmus Villemoes , Valentin Schneider , Sven Schnelle , Russell King Subject: Re: [PATCH v4 3/4] lib/find_bit: optimize find_next_bit() functions Message-ID: References: <20220915020730.852234-1-yury.norov@gmail.com> <20220915020730.852234-4-yury.norov@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220915020730.852234-4-yury.norov@gmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 14, 2022 at 07:07:29PM -0700, Yury Norov wrote: > Over the past couple years, the function _find_next_bit() was extended > with parameters that modify its behavior to implement and- zero- and le- > flavors. The parameters are passed at compile time, but current design > prevents a compiler from optimizing out the conditionals. > > As find_next_bit() API grows, I expect that more parameters will be added. > Current design would require more conditional code in _find_next_bit(), > which would bloat the helper even more and make it barely readable. > > This patch replaces _find_next_bit() with a macro FIND_NEXT_BIT, and adds > a set of wrappers, so that the compile-time optimizations become possible. > > The common logic is moved to the new macro, and all flavors may be > generated by providing a FETCH macro parameter, like in this example: > > #define FIND_NEXT_BIT(FETCH, MUNGE, size, start) ... > > find_next_xornot_and_bit(addr1, addr2, addr3, size, start) > { > return FIND_NEXT_BIT(addr1[idx] ^ ~addr2[idx] & addr3[idx], > /* nop */, size, start); > } > > The FETCH may be of any complexity, as soon as it only refers the bitmap(s) > and an iterator idx. > > MUNGE is here to support _le code generation for BE builds. May be > empty. > > I ran find_bit_benchmark 16 times on top of 6.0-rc2 and 16 times on top > of 6.0-rc2 + this series. The results for kvm/x86_64 are: > > v6.0-rc2 Optimized Difference Z-score > Random dense bitmap ns ns ns % > find_next_bit: 787735 670546 117189 14.9 3.97 > find_next_zero_bit: 777492 664208 113284 14.6 10.51 > find_last_bit: 830925 687573 143352 17.3 2.35 > find_first_bit: 3874366 3306635 567731 14.7 1.84 > find_first_and_bit: 40677125 37739887 2937238 7.2 1.36 > find_next_and_bit: 347865 304456 43409 12.5 1.35 > > Random sparse bitmap > find_next_bit: 19816 14021 5795 29.2 6.10 > find_next_zero_bit: 1318901 1223794 95107 7.2 1.41 > find_last_bit: 14573 13514 1059 7.3 6.92 > find_first_bit: 1313321 1249024 64297 4.9 1.53 > find_first_and_bit: 8921 8098 823 9.2 4.56 > find_next_and_bit: 9796 7176 2620 26.7 5.39 > > Where the statistics is significant (z-score > 3), the improvement > is ~15%. > > According to the bloat-o-meter, the Image size is 10-11K less: > > x86_64/defconfig: > add/remove: 32/14 grow/shrink: 61/782 up/down: 6344/-16521 (-10177) > > arm64/defconfig: > add/remove: 3/2 grow/shrink: 50/714 up/down: 608/-11556 (-10948) ... > /* Seems like you wanted this to be a kernel doc, but it isn't right now. > - * This is a common helper function for find_next_bit, find_next_zero_bit, and > - * find_next_and_bit. The differences are: > - * - The "invert" argument, which is XORed with each fetched word before > - * searching it for one bits. > - * - The optional "addr2", which is anded with "addr1" if present. > + * Common helper for find_next_bit() function family In such case this should start with a name of the macro * FIND_NEXT_BIT - ... > + * @FETCH: The expression that fetches and pre-processes each word of bitmap(s) > + * @MUNGE: The expression that post-processes a word containing found bit (may be empty) > + * @size: The bitmap size in bits > + * @start: The bitnumber to start searching at > */ ... > +#define FIND_NEXT_BIT(FETCH, MUNGE, size, start) \ > +({ \ > + unsigned long mask, idx, tmp, sz = (size), __start = (start); \ > + \ > + if (unlikely(__start >= sz)) \ > + goto out; \ > + \ > + mask = MUNGE(BITMAP_FIRST_WORD_MASK(__start)); \ > + idx = __start / BITS_PER_LONG; \ > + \ > + for (tmp = (FETCH) & mask; !tmp; tmp = (FETCH)) { \ > + if ((idx + 1) * BITS_PER_LONG >= sz) \ > + goto out; \ > + idx++; \ > + } \ > + \ > + sz = min(idx * BITS_PER_LONG + __ffs(MUNGE(tmp)), sz); \ > +out: \ I dunno if GCC expression limits the scope of goto labels, but on the safe side you can add a prefix to it, so it becomes: FIND_NEXT_BIT_out: (or alike). > + sz; \ > +}) ... > +unsigned long _find_next_zero_bit_le(const unsigned long *addr, unsigned > + long size, unsigned long offset) Usually we don't split parameters between lines. ... > +unsigned long _find_next_bit_le(const unsigned long *addr, unsigned > + long size, unsigned long offset) Ditto. -- With Best Regards, Andy Shevchenko