linux-kernel - Re: irq_fpu_usable() is irreliable

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Date:	Wed, 18 Nov 2015 07:55:08 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	"Jason A. Donenfeld" <Jason@...c4.com>
Cc:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: irq_fpu_usable() is irreliable

* Jason A. Donenfeld <Jason@...c4.com> wrote:

> [...] Recently I've been tracking down a problem in which irq_fpu_usable() 
> returns false, yet a stack trace shows the first function is the syscall entry 
> point. [...]

Is this 'problem' a performance problem (code not being able to use the FPU 
occasionally and hence sporadically performing poorly), or some sort of actual 
stability/correctness problem?

Also, what CPU does the test system have, Intel or AMD? The FPU behavior can be 
very different in the two cases.

Third, could you post such a problematic stack trace?

Thanks,

	Ingo
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