From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=AWL,BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,RCVD_IN_DNSWL_BLOCKED, SPF_HELO_PASS,SPF_PASS shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by dcvr.yhbt.net (Postfix) with ESMTP id CE78E1F4B4 for ; Tue, 12 Jan 2021 09:38:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390356AbhALJhv (ORCPT ); Tue, 12 Jan 2021 04:37:51 -0500 Received: from cloud.peff.net ([104.130.231.41]:53174 "EHLO cloud.peff.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389440AbhALJhv (ORCPT ); Tue, 12 Jan 2021 04:37:51 -0500 Received: (qmail 7341 invoked by uid 109); 12 Jan 2021 09:37:10 -0000 Received: from Unknown (HELO peff.net) (10.0.1.2) by cloud.peff.net (qpsmtpd/0.94) with ESMTP; Tue, 12 Jan 2021 09:37:10 +0000 Authentication-Results: cloud.peff.net; auth=none Received: (qmail 11348 invoked by uid 111); 12 Jan 2021 09:37:12 -0000 Received: from coredump.intra.peff.net (HELO sigill.intra.peff.net) (10.0.0.2) by peff.net (qpsmtpd/0.94) with (TLS_AES_256_GCM_SHA384 encrypted) ESMTPS; Tue, 12 Jan 2021 04:37:12 -0500 Authentication-Results: peff.net; auth=none Date: Tue, 12 Jan 2021 04:37:09 -0500 From: Jeff King To: Taylor Blau Cc: git@vger.kernel.org, jrnieder@gmail.com Subject: Re: [PATCH 20/20] pack-revindex.c: avoid direct revindex access in 'offset_to_pack_pos()' Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org On Fri, Jan 08, 2021 at 01:18:06PM -0500, Taylor Blau wrote: > To prepare for on-disk reverse indexes, remove a spot in > 'offset_to_pack_pos()' that looks at the 'revindex' array in 'struct > packed_git'. > > Even though this use of the revindex pointer is within pack-revindex.c, > this clean up is still worth doing. Since the 'revindex' pointer will be > NULL when reading from an on-disk reverse index (instead the > 'revindex_data' pointer will be mmaped to the 'pack-*.rev' file), this > call-site would have to include a conditional to lookup the offset for > position 'mi' each iteration through the search. > > So instead of open-coding 'pack_pos_to_offset()', call it directly from > within 'offset_to_pack_pos()'. This definitely makes sense in the long run. I could take or leave it as a final patch in _this_ series (as opposed to the first patch in a subsequent series adding the rev files). > do { > const unsigned mi = lo + (hi - lo) / 2; > - if (revindex[mi].offset == ofs) { > + off_t got = pack_pos_to_offset(p, mi); They're both constant-time, so performance should be the same big-O. The function has extra BUG() checks. I doubt those are measurable in practice, though. -Peff