Message-ID: <551BEED2.2080805@redhat.com>
Date: Wed, 01 Apr 2015 15:12:50 +0200
From: Denys Vlasenko <dvlasenk@redhat.com>
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To: Ingo Molnar <mingo@kernel.org>
CC: Linus Torvalds <torvalds@linux-foundation.org>,
        Steven Rostedt <rostedt@goodmis.org>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Andy Lutomirski <luto@amacapital.net>, Oleg Nesterov <oleg@redhat.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Alexei Starovoitov <ast@plumgrid.com>, Will Drewry <wad@chromium.org>,
        Kees Cook <keescook@chromium.org>, x86@kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/9] x86/asm/entry/32: Use PUSH instructions to build
 pt_regs on stack
References: <1427821211-25099-1-git-send-email-dvlasenk@redhat.com> <1427821211-25099-2-git-send-email-dvlasenk@redhat.com> <20150401085140.GC23916@gmail.com>
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On 04/01/2015 10:51 AM, Ingo Molnar wrote:
> 
> * Denys Vlasenko <dvlasenk@redhat.com> wrote:
> 
>> This mimics the recent similar 64-bit change.
>> Saves ~110 bytes of code.
>>
>> Patch was run-tested on 32 and 64 bits, Intel and AMD CPU.
>> I also looked at the diff of entry_64.o disassembly, to have
>> a different view of the changes.
> 
> The other important question would be: what performance difference (if 
> any) did you observe before/after the change?

I did not measure it then.

At the moment I don't have AMD CPUs here, cant benchmark
32-bit syscall-based codepath.

On a Sandy Bridge CPU (IOW: sysenter codepath) -

Before: 78.57 ns per getpid
After:  76.90 ns per getpid

It's better than I thought it would be.
Probably because this load:

movl	ASM_THREAD_INFO(TI_sysenter_return, %rsp, 0), %r10d

has been moved up by the patch (happens sooner).
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