linux-kernel - Re: [PATCH v4 RESEND] x86/asm/entry/32, selftests: Add 'test_syscall

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Date:	Mon, 14 Sep 2015 10:26:01 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Denys Vlasenko <dvlasenk@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>, Oleg Nesterov <oleg@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 RESEND] x86/asm/entry/32, selftests: Add
 'test_syscall_vdso' test


* Andy Lutomirski <luto@...capital.net> wrote:

> > (I'm not very comfortable about additional six push/pops
> > which are necessary for this to happen. I'm surprised
> > maintainers tentatively agreed to that -
> > I was grilled and asked to prove with measurements
> > that *one* additional push+pop wasn't adding significant overhead).
> 
> I suspect that I need to make the series faster.
> 
> Also, int $0x80 isn't a fast path for any legitimate use case except
> Debian, and I would argue that Debian is just buggy.

So buggy in the sense of not making use of faster syscalls, right? It won't break 
in any visible way, correct?

So if this heavy int80 syscall use happens even with the latest version of Debian 
as well then it would be nice to figure out what's wrong there, and provide an 
optimization patch to their libc guys or so - to make sure we fully understand the 
problem.

Thanks,

	Ingo
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