From: Jamie Lokier <email@example.com> To: Brian Gerst <firstname.lastname@example.org> Cc: Kathy Frazier <email@example.com>, Andi Kleen <firstname.lastname@example.org>, email@example.com Subject: Re: Interrupt doesn't make it to the 8259 on a ASUS P4PE mobo Date: Tue, 15 Jul 2003 18:43:37 +0100 [thread overview] Message-ID: <20030715174337.GC1491@mail.jlokier.co.uk> (raw) In-Reply-To: <3F14348B.firstname.lastname@example.org> Brian Gerst wrote: > >>>dmatimer.expires = jiffies + 0.5*HZ; > >> > >>That's a serious bug. You cannot use floating point in the kernel. > >>It will corrupt the FP state of the user process. > > > >HZ on the INTEL platform is 100, so this should simply add 50 to the > >current > >value of jiffies. Besides, assigning the value to the unsigned int field > >(expires) will truncate it to an integer anyway. > > Use HZ/2 instead. GCC doesn't optimize floating point constants to the > same degree it does integers, because it doesn't know what mode > (rounding, precision) the FPU is in. Optimising this to an integer add of 50 would be incorrect anyway. Think about jiffies == 0xfffffffe. The first statement is equivalent to: dmatimer.expires = (unsigned long) ((double) + 50) and would set dmatimer.expires to 0xffffffff. Whereas the HZ/2 form is correct! Have a nice day, -- Jamie
next prev parent reply other threads:[~2003-07-15 17:29 UTC|newest] Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <email@example.com> 2003-07-15 16:14 ` Kathy Frazier 2003-07-15 15:31 ` Richard B. Johnson 2003-07-15 15:58 ` SCSI ATA driver in 2.4.22 ? Jeff Mock 2003-07-15 16:14 ` Jeff Garzik 2003-07-15 17:06 ` Interrupt doesn't make it to the 8259 on a ASUS P4PE mobo Brian Gerst 2003-07-15 17:43 ` Jamie Lokier [this message] 2003-07-15 17:59 ` Luciano Miguel Ferreira Rocha 2003-07-15 18:24 ` Brian Gerst 2003-07-15 18:44 ` Alan Cox 2003-07-15 19:44 ` Jamie Lokier 2003-07-20 21:04 ` Riley Williams 2003-07-20 22:25 ` Jeremy Fitzhardinge [not found] <Pine.LNX.4.53.0307141833190.4354@chaos> 2003-07-15 16:52 ` Kathy Frazier 2003-07-14 21:35 Kathy Frazier
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