From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by sourceware.org (Postfix) with ESMTPS id 6CBC63858C54 for ; Wed, 27 Apr 2022 10:47:52 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 6CBC63858C54 Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-609-Gt1iWisgO6-nsVqv6fXIaA-1; Wed, 27 Apr 2022 06:47:50 -0400 X-MC-Unique: Gt1iWisgO6-nsVqv6fXIaA-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id B22A88039D7; Wed, 27 Apr 2022 10:47:49 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.39.193.187]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D4CFE463E02; Wed, 27 Apr 2022 10:47:48 +0000 (UTC) From: Florian Weimer To: Noah Goldstein via Libc-alpha Subject: Re: [PATCH v3 5/6] nss: Optimize nss_hash in nss_hash.c References: <20220414041231.926415-1-goldstein.w.n@gmail.com> <20220425163601.3670626-1-goldstein.w.n@gmail.com> <20220425163601.3670626-5-goldstein.w.n@gmail.com> Date: Wed, 27 Apr 2022 12:47:46 +0200 In-Reply-To: <20220425163601.3670626-5-goldstein.w.n@gmail.com> (Noah Goldstein via Libc-alpha's message of "Mon, 25 Apr 2022 11:36:00 -0500") Message-ID: <87ee1iiyzx.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.85 on 10.11.54.10 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Spam-Status: No, score=-11.1 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, RCVD_IN_DNSWL_LOW, SPF_HELO_NONE, SPF_NONE, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 27 Apr 2022 10:47:53 -0000 * Noah Goldstein via Libc-alpha: > diff --git a/nss/nss_hash.c b/nss/nss_hash.c > index 27a348ea9b..c6a375f386 100644 > --- a/nss/nss_hash.c > +++ b/nss/nss_hash.c > @@ -19,58 +19,63 @@ > > /* This is from libc/db/hash/hash_func.c, hash3 is static there */ > /* > - * This is INCREDIBLY ugly, but fast. We break the string up into 8 byte > + * This is INCREDIBLY ugly, but fast. We break the string up into 4 byte > * units. On the first time through the loop we get the "leftover bytes" > - * (strlen % 8). On every other iteration, we perform 8 HASHC's so we handle > - * all 8 bytes. Essentially, this saves us 7 cmp & branch instructions. If > - * this routine is heavily used enough, it's worth the ugly coding. > + * (len % 4). On every other iteration, we perform a 4x unrolled version > + * HASHC. Further unrolling does not appear to help. I wonder if this optimization is worth it. This is used in the nscd interface only, right? dl_new_hash performance is at least important to symbol lookup. Thanks, Florian