From: David Edelsohn <dje@watson.ibm.com>
To: Paul Koning <pkoning@xedia.com>
Cc: law@cygnus.com, crux@Pool.Informatik.RWTH-Aachen.DE, egcs@cygnus.com
Subject: Re: Some Haifa scheduler bugs
Date: Wed, 03 Sep 1997 11:50:00 -0000 [thread overview]
Message-ID: <9709031849.AA23508@rios1.watson.ibm.com> (raw)
In-Reply-To: <9709031838.AA27038@kona.>
>>>>> Paul Koning writes:
Paul> "law@cygnus.com" wrote:
>> However, for execution tests that fail, I wonder how many (if any) are
>> caused by -fsched-spec-load-dangerous. If I remember right that
>> relies on the OS to support non-faulting loads from zero.
Paul> If that switch indeed depends on not faulting references to zero, it
Paul> probably isn't worth having. Or if it's kept it needs a warning that
Paul> in many OS's it will fail. The reason is that faulting on references
Paul> to zero is universally considered a Good Thing and many OS's go out of
Paul> their way to provide that feature.
I disagree with your justification that faulting on dereferncing
address zero is considered a Good Thing. This depends on your priorities
and the correctness of your program. I do not want to get into a general
discussion about programming styles and kernel design, but speculatively
dereferencing zero is very important for good performance on some systems;
some operating systems go out of their way specifically to make page zero
valid, as opposed to making it a VM error. This needs to be set in the
configuation file on a system-by-system basis and not universally enabled
or disabled.
David
next prev parent reply other threads:[~1997-09-03 11:50 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <Pine.SOL.3.90.970826140826.2901J-100000@maigret.informatik.rwth-aachen.de>
1997-09-01 20:33 ` Jeffrey A Law
1997-09-03 9:30 ` Bernd Schmidt
1997-09-03 9:37 ` Jeffrey A Law
1997-09-03 9:44 ` Bernd Schmidt
1997-09-03 10:07 ` Jeffrey A Law
1997-09-05 7:15 ` Bernd Schmidt
1997-09-05 7:55 ` Jeffrey A Law
1997-09-05 8:33 ` Ian Lance Taylor
1997-09-03 11:58 ` Jim Wilson
1997-09-04 1:16 ` regparm & other gcc bug Martynas Kunigelis
1997-09-05 9:29 ` Kamil Iskra
1997-09-06 5:19 ` Martynas Kunigelis
1997-09-03 11:39 ` Some Haifa scheduler bugs Paul Koning
1997-09-03 11:50 ` David Edelsohn [this message]
1997-09-03 13:13 ` Richard Henderson
1997-09-03 13:19 ` Jeffrey A Law
1997-09-04 9:33 ` Craig Burley
1997-09-04 11:12 ` Jeffrey A Law
1997-09-04 11:33 ` David S. Miller
1997-09-04 14:38 ` David Edelsohn
1997-09-04 11:27 meissner
[not found] <Pine.SOL.3.90.970826141030.2901K-100000@maigret.informatik.rwth-aachen.de>
1997-09-01 20:42 ` Jeffrey A Law
-- strict thread matches above, loose matches on Subject: below --
1997-08-26 14:34 Bernd Schmidt
1997-08-22 13:53 Building of generated parser files Andreas Schwab
1997-08-22 15:02 ` Some Haifa scheduler bugs Jeffrey A Law
1997-08-22 15:24 ` Jeffrey A Law
1997-08-22 10:48 Building of generated parser files Niklas Hallqvist
1997-08-22 13:28 ` Some Haifa scheduler bugs Bernd Schmidt
1997-08-21 16:51 Problems on PowerPC David Edelsohn
1997-08-21 17:43 ` Some Haifa scheduler bugs Jeffrey A Law
1997-08-21 15:20 egcs repository Joel Sherrill
1997-08-21 15:47 ` Some Haifa scheduler bugs Bernd Schmidt
1997-08-19 19:00 Jeffrey A Law
1997-08-19 17:54 Jeffrey A Law
1997-08-19 7:36 egcs: A new compiler project to merge the existing GCC forks (fwd) Robert Wilhelm
1997-08-19 9:34 ` Some Haifa scheduler bugs Bernd Schmidt
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