linux-kernel - Re: [BUG] Why does mwait_idle_with_hints() call MWAIT with interrupts disabled ?

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Message-ID: <CAM3a_ypSgCuf_8z82MKAt=9DXhz5fih-QYMLCrOVf+bBGde4Rg@mail.gmail.com>
Date:	Mon, 11 Jul 2011 13:32:53 +0530
From:	Tomar <tomar@...uxsmiths.com>
To:	Mike Galbraith <efault@....de>
Cc:	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [BUG] Why does mwait_idle_with_hints() call MWAIT with interrupts
 disabled ?

Mike,
        Thanks for pointing. This explains it. I was looking at an
older manual which did not have mention of this ECX extension.

Thanks,
Tomar



> I got curious enough to blow an inch of virtual dust off the manual..
>
> Software_Delelopers_Manual_Volume:2A:Instruction_Set_Reference:A-M
>
> MWAIT for Address Range Monitoring
>
> For address-range monitoring, the MWAIT instruction operates with the MONITOR
> instruction. The two instructions allow the definition of an address at which to wait
> (MONITOR) and a implementation-dependent-optimized operation to commence at
> the wait address (MWAIT). The execution of MWAIT is a hint to the processor that it
> can enter an implementation-dependent-optimized state while waiting for an event
> or a store operation to the address range armed by MONITOR.
> ECX specifies optional extensions for the MWAIT instruction. EAX may contain hints
> such as the preferred optimized state the processor should enter.
> For Pentium 4 processors (CPUID signature family 15 and model 3), non-zero values
> for EAX and ECX are reserved. Later processors defined ECX=1 as a valid extension
> (see below).
>
> A store to the address range armed by the MONITOR instruction, an interrupt, an NMI
> or SMI, a debug exception, a machine check exception, the BINIT# signal, the INIT#
> signal, or the RESET# signal will exit the implementation-dependent-optimized
> state. An interrupt will cause the processor to exit only if the state was entered with
> interrupts enabled or if ECX=1.
>                   ^^^^^^^^^^^
>
>
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