Messages in this thread | | | From | David Mosberger <> | Date | Wed, 31 Mar 2004 10:06:00 -0800 | Subject | Re: 2.4.21 on Itanium2: floating-point assist fault at ip 400000000062ada1, isr 0000020000000008 |
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>>>>> On Wed, 31 Mar 2004 19:00:17 +0200, Denis Vlasenko <vda@port.imtp.ilyichevsk.odessa.ua> said:
Denis> kernel says that you have them too frequently, which probably Denis> impairs efficiency. It's a hint to programmer.
Close: the kernel limits the frequency of the printing to avoid flooding the log files. Even if you do get the faults frequently, it won't print more than 5 warning messages every 5 seconds. The floating-point software-assist (fpswa) faults are harmless in the sense that they don't affect correctness of the program, but if you do get them _very_ frequently (which is quite rare), they could impair performance. FPSWA faults occur only for corner-cases of floating-point arithmetic, such as operations on denormals or non-finite numbers. Many programs don't need denormal support at all and for those, you can link the program with -ffast-math (GCC) or -ftz (Intel compiler). This will turn on "flush-to-zero" mode and avoid any FPSWA-faults due to denormals (in x86-speak, this is equivalent to the "flush-to-zero" mode that SSE offers).
If the messages appear with a frequency of less than 5 messages/5 seconds, then there is certainly no performance issue and you may want to just turn off the messages. This can be done via the prctl(2) system-call or with the prctl command. With the latter:
prctl --fp-emul=silent
will fork a new shell and disable the printing of the FPSWA-messages in the shell and all its children. There is also "--unaligned=silent" which will turn off a similar message for unaligned access emulation done by the kernel.
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