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Date: Wed, 30 Aug 2006 22:03:54 +0200 From: Willy Tarreau <w@....eu> To: Andi Kleen <ak@...e.de> Cc: pageexec@...email.hu, davej@...hat.com, linux-kernel@...r.kernel.org Subject: Re: [PATCH][RFC] exception processing in early boot On Wed, Aug 30, 2006 at 09:36:54PM +0200, Andi Kleen wrote: > > > Andi, if you remove the HLT here, some CPUs will spin at full speed. This > > is nasty during boot because some of them might not have enabled their > > fans yet for instance > > That would be a severe bug in the platform. Basically always the fans are managed > by SMM code. It was just an example. Other examples include virtual machines never stopping because they will see the guest is working and not halted. Anyway, the "hlt;jmp $" is already used in boot/setup.S, and the HLT bug you have pointed is, as explained by Richard, a problem preventing some CPUs from WAKING up from HLT. It causes a problem when HLT is used in the idle loop. Users who have this problem must pass the "no-hlt" command line option, otherwise their CPU will halt during the idle loop (which is the effect we're looking for), and those without the bug (those who don't have to pass "no-hlt") will also have the HLT working. So, to conclude, with or without the bug, "hlt;jmp $" will halt the CPU as we expect it to. Therefore, I'd like you to restore it in the patch. Thanks, Willy - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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