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 [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id A8BEA3858D3C for ; Tue, 7 Dec 2021 14:50:18 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org A8BEA3858D3C Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-588-D-gLmshsO6qnUXpiiwDnBQ-1; Tue, 07 Dec 2021 09:50:15 -0500 X-MC-Unique: D-gLmshsO6qnUXpiiwDnBQ-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A205A804162; Tue, 7 Dec 2021 14:50:12 +0000 (UTC) Received: from tucnak.zalov.cz (unknown [10.39.194.188]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 119FE5445E; Tue, 7 Dec 2021 14:50:11 +0000 (UTC) Received: from tucnak.zalov.cz (localhost [127.0.0.1]) by tucnak.zalov.cz (8.16.1/8.16.1) with ESMTPS id 1B7Eo8LO2762444 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NOT); Tue, 7 Dec 2021 15:50:09 +0100 Received: (from jakub@localhost) by tucnak.zalov.cz (8.16.1/8.16.1/Submit) id 1B7Eo8Kg2762443; Tue, 7 Dec 2021 15:50:08 +0100 Date: Tue, 7 Dec 2021 15:50:07 +0100 From: Jakub Jelinek To: Richard Biener , Jeff Law , gcc-patches@gcc.gnu.org Subject: Re: [PATCH] pch: Add support for relocation of the PCH data [PR71934] Message-ID: <20211207145007.GX2646553@tucnak> Reply-To: Jakub Jelinek References: <20211207095507.GV2646553@tucnak> MIME-Version: 1.0 In-Reply-To: <20211207095507.GV2646553@tucnak> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Spam-Status: No, score=-5.6 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H2, 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: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 07 Dec 2021 14:50:20 -0000 On Tue, Dec 07, 2021 at 10:55:07AM +0100, Jakub Jelinek via Gcc-patches wrote: > So, this patch instead builds a relocation table (sorted list of addresses > in the blob which needs relocation) at PCH save time, stores it in a very > compact form into the gch file and upon restore, adjusts pointers in GTY > roots (that is right away in the root structures) and the addresses in the > relocation table. > The cost on stdc++.gch/O2g.gch (previously 85MB large) is about 3% file size > growth, there are 2.5 million pointers that need relocation in the gch blob > and the relocation table uses uleb128 for address deltas and needs ~1.01 bytes > for one address that needs relocation, and about 20% compile time during > PCH save (I think it is mainly because of the need to qsort those 2.5 > million pointers). On PCH restore, if it doesn't need relocation (the usual > case), it is just an extra fread of sizeof (size_t) data and fseek > (in my tests real time on vanilla tree for #include CU > was ~0.175s and with the patch but no relocation ~0.173s), while if it needs > relocation it took ~0.193s, i.e. 11.5% slower. I'll note that without PCH that #include int i; testcase compiles with -O2 -g in ~1.199s, i.e. 6.2 times slower than PCH with relocation and 6.9 times than PCH without relocation. Jakub