linux-kernel - Re: [PATCH 4/5] x86: entry_64.S: always allocate complete "struct pt

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Message-ID: <CAK1hOcML4guky7VutK1xc3YxNjy4K4bX_78p8+7rEhMW0ZuLdg@mail.gmail.com>
Date:	Sat, 2 Aug 2014 00:11:08 +0200
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Denys Vlasenko <dvlasenk@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Frederic Weisbecker <fweisbec@...il.com>,
	X86 ML <x86@...nel.org>, Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH 4/5] x86: entry_64.S: always allocate complete "struct pt_regs"

On Fri, Aug 1, 2014 at 8:35 PM, H. Peter Anvin <hpa@...or.com> wrote:
> On 08/01/2014 07:48 AM, Denys Vlasenko wrote:
>>
>> Patch was run-tested: 64-bit executables, 32-bit executables,
>> strace works.
>>
>
> Could you please try to see if there is a measurable change in the
> latency of a trivial syscall?

Will do.
Something along the lines of "how long does it take to execute two
gazillions of getppid()?"

I'll send v2 shortly - I just figured out what was this mysterious
dance with allocating "not-quite-full struct pt_regs" on interrupt path:
It is intended to make nested interrupts to have better
backtraces. I broke that by this patch, v2 will have this feature retained.
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