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 <rguent...@suse.de> wrote:
> > > On Wed, 6 Apr 2016, Prathamesh Kulkarni wrote:
> > >
> > >> On 5 April 2016 at 18:28, Richard Biener <rguent...@suse.de> wrote:
> > >> > On Tue, 5 Apr 2016, Prathamesh Kulkarni wrote:
> > >> >
> > >> >> On 5 April 2016 at 16:58, Richard Biener <rguent...@suse.de> wrote:
> > >> >> > On Tue, 5 Apr 2016, Prathamesh Kulkarni wrote:
> > >> >> >
> > >> >> >> On 4 April 2016 at 19:44, Jan Hubicka <hubi...@ucw.cz> 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.
