linux-kernel - Re: For your amusement: slightly faster syscalls

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Date:	Thu, 18 Jun 2015 10:48:34 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Denys Vlasenko <vda.linux@...glemail.com>,
	Borislav Petkov <bp@...en8.de>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: For your amusement: slightly faster syscalls


* Ingo Molnar <mingo@...nel.org> wrote:

> 
> * Andy Lutomirski <luto@...capital.net> wrote:
> 
> > On Mon, Jun 15, 2015 at 2:42 PM, H. Peter Anvin <hpa@...or.com> wrote:
> > > On 06/15/2015 02:30 PM, Linus Torvalds wrote:
> > >>
> > >> On Jun 12, 2015 2:09 PM, "Andy Lutomirski" <luto@...capital.net
> > >> <mailto:luto@...capital.net>> wrote:
> > >>>
> > >>> Caveat emptor: it also disables SMP.
> > >>
> > >> OK, I don't think it's interesting in that form.
> > >>
> > >> For small cpu counts, I guess we could have per-cpu syscall entry points 
> > >> (unless the syscall entry msr is shared across hyperthreading? Some msr's are 
> > >> per thread, others per core, AFAIK), and it could actually work that way.
> > >>
> > >> But I'm not sure the three cycles is worth the worry and the complexity.
> > >
> > > We discussed the per-cpu syscall entry point, and the issue at hand is that it 
> > > is very hard to do that without with fairly high probability touch another 
> > > cache line and quite possibly another page (and hence a TLB entry.)
> 
> ( So apparently I wasn't Cc:ed, or gmail ate the mail - so I can only guess from 
>   the surrounding discussion what this patch does, as my lkml folder is still 
>   doing a long refresh ... )

Hm, it's nowhere to be found. Could someone please forward me the original email?

Thanks,

	Ingo
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