Re: [PATCH 2/9] x86/asm/entry/32: Use PUSH instructions to build pt_regs on stack

From: Denys Vlasenko
Date: Wed Apr 01 2015 - 09:13:31 EST

On 04/01/2015 10:51 AM, Ingo Molnar wrote:
> * Denys Vlasenko <dvlasenk@xxxxxxxxxx> 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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