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Message-ID: <3E000EF9.8070001@quark.didntduck.org>
Date: Wed, 18 Dec 2002 01:00:25 -0500
From: Brian Gerst <bgerst@quark.didntduck.org>
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To: Ulrich Drepper <drepper@redhat.com>
CC: "Nakajima, Jun" <jun.nakajima@intel.com>,
       Linus Torvalds <torvalds@transmeta.com>,
       Matti Aarnio <matti.aarnio@zmailer.org>,
       Hugh Dickins <hugh@veritas.com>, Dave Jones <davej@codemonkey.org.uk>,
       Ingo Molnar <mingo@elte.hu>, linux-kernel@vger.kernel.org,
       hpa@transmeta.com
Subject: Re: Intel P6 vs P7 system call performance
References: <3014AAAC8E0930438FD38EBF6DCEB564419C95@fmsmsx407.fm.intel.com> <3DFFD55E.6020305@redhat.com>
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Ulrich Drepper wrote:
> Nakajima, Jun wrote:
> 
>>AMD (at least Athlon, as far as I know) supports sysenter/sysexit. We tested it on an Athlon box as well, and it worked fine. And sysenter/sysexit was better than int/iret too (about 40% faster) there. 
> 
> 
> That's good to know but not what I meant.
> 
> I referred to syscall/sysret opcodes.  They are broken in their own way
> (destroying ecx on kernel entry) but at least they preserve eip.
> 

syscall is pretty much unusable unless the NMI is changed to a task 
gate.  syscall does not change %esp on entry to the kernel, so an NMI 
before the manual stack switch would still use the user stack, which is 
not guaranteed to be valid - oops.  x86-64 gets around this by using an 
interrupt stack, its replacement for task gates.

--
				Brian Gerst

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