From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 49893 invoked by alias); 6 Apr 2016 09:24:52 -0000 Mailing-List: contact gcc-patches-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-patches-owner@gcc.gnu.org Received: (qmail 49874 invoked by uid 89); 6 Apr 2016 09:24:51 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-2.9 required=5.0 tests=BAYES_00,RCVD_IN_DNSWL_NONE,RP_MATCHES_RCVD,SPF_PASS autolearn=ham version=3.3.2 spammy=million, ten, late X-HELO: mx2.suse.de Received: from mx2.suse.de (HELO mx2.suse.de) (195.135.220.15) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (CAMELLIA256-SHA encrypted) ESMTPS; Wed, 06 Apr 2016 09:24:41 +0000 Received: from relay1.suse.de (charybdis-ext.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 20697AC13; Wed, 6 Apr 2016 09:24:37 +0000 (UTC) Date: Wed, 06 Apr 2016 09:24:00 -0000 From: Richard Biener To: Prathamesh Kulkarni cc: Jan Hubicka , gcc Patches , Ramana Radhakrishnan Subject: Re: [RFC] introduce --param max-lto-partition for having an upper bound on partition size In-Reply-To: Message-ID: References: <20160404120030.GD14122@kam.mff.cuni.cz> <20160404141436.GB95176@kam.mff.cuni.cz> User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-SW-Source: 2016-04/txt/msg00282.txt.bz2 On Wed, 6 Apr 2016, Richard Biener wrote: > On Wed, 6 Apr 2016, Prathamesh Kulkarni wrote: > > > On 6 April 2016 at 13:44, Richard Biener wrote: > > > On Wed, 6 Apr 2016, Prathamesh Kulkarni wrote: > > > > > >> On 5 April 2016 at 18:28, Richard Biener wrote: > > >> > On Tue, 5 Apr 2016, Prathamesh Kulkarni wrote: > > >> > > > >> >> On 5 April 2016 at 16:58, Richard Biener wrote: > > >> >> > On Tue, 5 Apr 2016, Prathamesh Kulkarni wrote: > > >> >> > > > >> >> >> On 4 April 2016 at 19:44, Jan Hubicka wrote: > > >> >> >> > > > >> >> >> >> diff --git a/gcc/lto/lto-partition.c b/gcc/lto/lto-partition.c > > >> >> >> >> index 9eb63c2..bc0c612 100644 > > >> >> >> >> --- a/gcc/lto/lto-partition.c > > >> >> >> >> +++ b/gcc/lto/lto-partition.c > > >> >> >> >> @@ -511,9 +511,20 @@ lto_balanced_map (int n_lto_partitions) > > >> >> >> >> varpool_order.qsort (varpool_node_cmp); > > >> >> >> >> > > >> >> >> >> /* Compute partition size and create the first partition. */ > > >> >> >> >> + if (PARAM_VALUE (MIN_PARTITION_SIZE) > PARAM_VALUE (MAX_PARTITION_SIZE)) > > >> >> >> >> + fatal_error (input_location, "min partition size cannot be greater than max partition size"); > > >> >> >> >> + > > >> >> >> >> partition_size = total_size / n_lto_partitions; > > >> >> >> >> if (partition_size < PARAM_VALUE (MIN_PARTITION_SIZE)) > > >> >> >> >> partition_size = PARAM_VALUE (MIN_PARTITION_SIZE); > > >> >> >> >> + else if (partition_size > PARAM_VALUE (MAX_PARTITION_SIZE)) > > >> >> >> >> + { > > >> >> >> >> + n_lto_partitions = total_size / PARAM_VALUE (MAX_PARTITION_SIZE); > > >> >> >> >> + if (total_size % PARAM_VALUE (MAX_PARTITION_SIZE)) > > >> >> >> >> + n_lto_partitions++; > > >> >> >> >> + partition_size = total_size / n_lto_partitions; > > >> >> >> >> + } > > >> >> >> > > > >> >> >> > lto_balanced_map actually works in a way that looks for cheapest cutpoint in range > > >> >> >> > 3/4*parittion_size to 2*partition_size and picks the cheapest range. > > >> >> >> > Setting partition_size to this value will thus not cause partitioner to produce smaller > > >> >> >> > partitions only. I suppose modify the conditional: > > >> >> >> > > > >> >> >> > /* Partition is too large, unwind into step when best cost was reached and > > >> >> >> > start new partition. */ > > >> >> >> > if (partition->insns > 2 * partition_size) > > >> >> >> > > > >> >> >> > and/or in the code above set the partition_size to half of total_size/max_size. > > >> >> >> > > > >> >> >> > I know this is somewhat sloppy. This was really just first cut implementation > > >> >> >> > many years ago. I expected to reimplement it marter soon, but then there was > > >> >> >> > never really a need for it (I am trying to avoid late IPA optimizations so the > > >> >> >> > partitioning decisions should mostly affect compile time performance only). > > >> >> >> > If ARM is more sensitive for partitining, perhaps it would make sense to try to > > >> >> >> > look for something smarter. > > >> >> >> > > > >> >> >> >> + > > >> >> >> >> npartitions = 1; > > >> >> >> >> partition = new_partition (""); > > >> >> >> >> if (symtab->dump_file) > > >> >> >> >> diff --git a/gcc/lto/lto.c b/gcc/lto/lto.c > > >> >> >> >> index 9dd513f..294b8a4 100644 > > >> >> >> >> --- a/gcc/lto/lto.c > > >> >> >> >> +++ b/gcc/lto/lto.c > > >> >> >> >> @@ -3112,6 +3112,12 @@ do_whole_program_analysis (void) > > >> >> >> >> timevar_pop (TV_WHOPR_WPA); > > >> >> >> >> > > >> >> >> >> timevar_push (TV_WHOPR_PARTITIONING); > > >> >> >> >> + > > >> >> >> >> + if (flag_lto_partition != LTO_PARTITION_BALANCED > > >> >> >> >> + && PARAM_VALUE (MAX_PARTITION_SIZE) != INT_MAX) > > >> >> >> >> + fatal_error (input_location, "--param max-lto-partition should only" > > >> >> >> >> + " be used with balanced partitioning\n"); > > >> >> >> >> + > > >> >> >> > > > >> >> >> > I think we should wire in resonable MAX_PARTITION_SIZE default. THe value you > > >> >> >> > found experimentally may be a good start. For that reason we can't really > > >> >> >> > refuse a value when !LTO_PARTITION_BALANCED. Just document it as parameter for > > >> >> >> > balanced partitioning only and add a parameter to lto_balanced_map specifying whether > > >> >> >> > this param should be honored (because the same path is used for partitioning to one partition) > > >> >> >> > > > >> >> >> > Otherwise the patch looks good to me modulo missing documentation. > > >> >> >> Thanks for the review. I have updated the patch. > > >> >> >> Does this version look OK ? > > >> >> >> I had randomly chosen 10000, not sure if that's an appropriate value > > >> >> >> for default. > > >> >> > > > >> >> > I think it's way too small. This is roughly the number of GIMPLE stmts > > >> >> > (thus roughly the number of instructions). So with say a 8 byte > > >> >> > instruction format it is on the order of 80kB. You'd want to have a > > >> >> > default of at least several ten times of large-unit-insns (also 10000). > > >> >> > I'd choose sth like 1000000 (one million). I find the lto-min-partition > > >> >> > number quite small as well (and up it by a factor of 10). > > >> >> Done in this version. > > >> > > > >> > I'd do that separately. > > >> > > > >> > Please no default parameter for lto_balanced_map (), instead change > > >> > all callers. > > >> > > > >> >> Is it OK after bootstrap+test ? > > >> > > > >> > Note that this is for stage1 only. I'll leave approval to Honza > > >> > (also verification of the default max param - not sure if for example > > >> > chromium or firefox should/will be split to more than 32 partitions > > >> > with the patch) > > >> Removed default parameter in this version. I verified with the patch > > >> for chromium LTO build: > > >> n_lto_partitions == 32, ltrans_partitions.length() == 31 > > > > > > Just noticed that lto_balanced_map already gets PARAM_LTO_PARTITIONS, > > > so why not pass it PARAM_MAX_PARTITION_SIZE or 0 (as magic value for > > > unlimited) instead of a bool parameter? > > Indeed. Instead of 0, would it be OK to pass INT_MAX as 2nd parameter in case > > of single partition, since in that case partition->insns > > > max_partition_size will never > > be true, which would effectively ignore max_partition_size. > > You mean we are limited to INT_MAX partition size anyway, even on 64bit > systems? ... (but yes, using a suitable large number works as well) Ah, even 'total_size' is an int ... I wonder what this means for LTOing a -mcmodel=large app (that really needs the large model). Richard.