linux-kernel - Re: [uml-devel] SYSCALL, ptrace and syscall restart breakages (Re: [RFC] weird crap with vdso on uml/i386)

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Date:	Wed, 24 Aug 2011 14:10:04 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <bp@...64.org>
CC:	Andrew Lutomirski <luto@....edu>,
	Al Viro <viro@...iv.linux.org.uk>,
	Ingo Molnar <mingo@...nel.org>,
	"user-mode-linux-devel@...ts.sourceforge.net" 
	<user-mode-linux-devel@...ts.sourceforge.net>,
	Richard Weinberger <richard@....at>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...hat.com" <mingo@...hat.com>
Subject: Re: [uml-devel] SYSCALL, ptrace and syscall restart breakages (Re:
 [RFC] weird crap with vdso on uml/i386)

On 08/23/2011 02:10 PM, Borislav Petkov wrote:
> On Tue, Aug 23, 2011 at 05:06:03PM -0400, H. Peter Anvin wrote:
>> On 08/23/2011 01:56 PM, Borislav Petkov wrote:
>>>
>>> But no, I don't think the difference has disappeared - to the contrary,
>>> AFAICT, the intention is for SYSCALL to be the fastest way to do
>>> syscalls on x86 due to diminished number of segment checks etc. INT80
>>> is legacy, slower, etc. I believe Andy measured a similar situation on
>>> Sandy Bridge with SYSCALL having latencies in the tens of nsecs range
>>> and INT80 being much slower. Ingo also measured a similar situation
>>> where the latency gap between the two on Intel is even bigger.
>>>
>>
>> Sandy Bridge doesn't have SYSCALL32 at all.  It has SYSENTER and SYSCALL64.
> 
> Yeah, I was talking about SYSCALL in general.
> 

By the way, Borislav;

any way you could nudge your hardware people into

a) supporting SYSENTER in compatibility mode, and
b) giving us a way to turn SYSCALL *off* in compat mode?

... for future chips?

	-hpa
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