Messages in this thread | | | Date | Wed, 01 Apr 2015 15:12:50 +0200 | From | Denys Vlasenko <> | Subject | Re: [PATCH 2/9] x86/asm/entry/32: Use PUSH instructions to build pt_regs on stack |
| |
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).
| |