From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 843 invoked by alias); 26 Feb 2004 22:28:23 -0000 Mailing-List: contact gdb-patches-help@sources.redhat.com; run by ezmlm Precedence: bulk List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sources.redhat.com Received: (qmail 828 invoked from network); 26 Feb 2004 22:28:22 -0000 Received: from unknown (HELO mx1.redhat.com) (66.187.233.31) by sources.redhat.com with SMTP; 26 Feb 2004 22:28:22 -0000 Received: from int-mx1.corp.redhat.com (int-mx1.corp.redhat.com [172.16.52.254]) by mx1.redhat.com (8.11.6/8.11.6) with ESMTP id i1QMSMb07613 for ; Thu, 26 Feb 2004 17:28:22 -0500 Received: from zenia.home.redhat.com (porkchop.devel.redhat.com [172.16.58.2]) by int-mx1.corp.redhat.com (8.11.6/8.11.6) with ESMTP id i1QMSK810076; Thu, 26 Feb 2004 17:28:21 -0500 To: Daniel Jacobowitz Cc: gdb-patches@sources.redhat.com, Elena Zannoni Subject: Re: [RFA/dwarf] Optimize partial DIE reading for uninteresting DIEs References: <20040225030644.GA5167@nevyn.them.org> From: Jim Blandy Date: Thu, 26 Feb 2004 22:28:00 -0000 In-Reply-To: <20040225030644.GA5167@nevyn.them.org> Message-ID: User-Agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.3 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-SW-Source: 2004-02/txt/msg00781.txt.bz2 Daniel Jacobowitz writes: > read_partial_die is a pretty heavyweight function. One of the largest > indicators of this is how high read_uleb128 shows up in startup profiles. > This patch provides an alternative for DIEs we know are uninteresting: we > can just read in the abbrev, and the sibling pointer if any. > > Performancewise, on mainline this is a bit of a wash for typical code. > That's because we read every file-scope or namespace-scope DIE using > read_partial_die before we decide if it's interesting. A followup patch to > use peek_die_abbrev for that provides a several percent improvement in GDB > startup time. Hmm. If I'm reading this right, the only real difference between calling skip_children and calling locate_pdi_sibling is that the former calls skip_one_die to get past the attributes, while the latter calls read_partial_die. Is that right? skip_one_die: - stops skipping attributes as soon as it sees a sibling pointer, - doesn't read the attributes' values, and - doesn't examine the attributes to fill in a partial_die_info structure. But none of that really sounds too expensive, so I'm not surprised that this change alone is a wash, and I'm curious to see the followup patch. You haven't posted that yet, right? It bothers me that the patch would give us two separate form parsers. It would be nicer if we could just have one function that knows how to get the proper value of each attribute. Would it be possible for skip_one_die to call read_attribute, instead of writing out its own switch? Yes, that would allocate space for the blocks on dwarf2_tmp_obstack, but I think there are comments in dwarf2_build_psymtabs_hard explaining that this isn't significant. For most everything, read_attribute_value just hands out pointers into the info or string buffer. And you're still not going to be reading past any sibling attributes, so in the common case you'll never read much anyway.