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Re: No documentation of -fsched-pressure-algorithm
- From: Richard Sandiford <rdsandiford at googlemail dot com>
- To: nick clifton <nickc at redhat dot com>
- Cc: gcc at gcc dot gnu dot org
- Date: Tue, 01 May 2012 13:59:26 +0100
- Subject: Re: No documentation of -fsched-pressure-algorithm
- References: <87sjfl5gc6.fsf@Gift.fritz.box> <878vhdxgnm.fsf@talisman.home> <4F9FA0B1.4090004@redhat.com>
nick clifton <nickc@redhat.com> writes:
> Hi Richard,
>
>>> I have just noticed that the new -fsched-pressure-algorithm= gcc
>>> command line option is not documented in gcc/doc/invoke.texi. Was
>>> this an oversight ?
>>
>> No, it was deliberate. It's not supposed to be a user-level option.
>
> Then why is there a user-visible command line option ?
So that developers can experiment.
> Also - why shouldn't it be a user-level option ? In my experience gcc's
> instruction scheduling tends to be very sensitive to the algorithm being
> compiled. For some applications it does a good job, but for others it
> actually makes the performance worth. Being able to tune the behaviour
> of the scheduler (via the various -fsched-... options) has been very
> helpful in getting good benchmark results.
But the idea is that if you get good benchmark results with it
(as for A8, A9 and s390), you should enable it by default.
If it makes some things significantly better and some things
significantly worse, we should look at why.
Richard