From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-x244.google.com (mail-pa0-x244.google.com [IPv6:2607:f8b0:400e:c03::244]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3sZXX85Z5fzDsWc for ; Thu, 15 Sep 2016 19:03:52 +1000 (AEST) Received: by mail-pa0-x244.google.com with SMTP id pp5so1888318pac.2 for ; Thu, 15 Sep 2016 02:03:52 -0700 (PDT) From: Nicholas Piggin To: Michael Ellerman , linuxppc-dev@lists.ozlabs.org Cc: Nicholas Piggin , Michael Neuling Subject: [PATCH] powerpc/64s: optimise syscall entry for virtual, relocatable case Date: Thu, 15 Sep 2016 19:03:21 +1000 Message-Id: <20160915090321.787-1-npiggin@gmail.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , The mflr r10 instruction was left over saving of lr when the code used lr to branch to system_call_entry from the exception handler. That was changed by 6a404806d to use the count register. The value is never used now, so mflr can be removed, and r10 can be used for storage rather than spilling to the SPR scratch register. The scratch register spill causes a long pipeline stall due to the SPR read after write. This change brings getppid syscall cost from 406 to 376 cycles on POWER8. getppid for non-relocatable case is 371 cycles. Signed-off-by: Nicholas Piggin --- arch/powerpc/kernel/exceptions-64s.S | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-) diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S index df6d45e..2cdd64f 100644 --- a/arch/powerpc/kernel/exceptions-64s.S +++ b/arch/powerpc/kernel/exceptions-64s.S @@ -63,15 +63,12 @@ END_FTR_SECTION_IFSET(CPU_FTR_REAL_LE) \ * is volatile across system calls. */ #define SYSCALL_PSERIES_2_DIRECT \ - mflr r10 ; \ ld r12,PACAKBASE(r13) ; \ LOAD_HANDLER(r12, system_call_entry) ; \ mtctr r12 ; \ mfspr r12,SPRN_SRR1 ; \ - /* Re-use of r13... No spare regs to do this */ \ - li r13,MSR_RI ; \ - mtmsrd r13,1 ; \ - GET_PACA(r13) ; /* get r13 back */ \ + li r10,MSR_RI ; \ + mtmsrd r10,1 ; \ bctr ; #else /* We can branch directly */ -- 2.9.3