From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-x242.google.com (mail-pf0-x242.google.com [IPv6:2607:f8b0:400e:c00::242]) (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 3wn94z34qRzDqLk for ; Tue, 13 Jun 2017 23:06:27 +1000 (AEST) Received: by mail-pf0-x242.google.com with SMTP id s66so6773068pfs.2 for ; Tue, 13 Jun 2017 06:06:27 -0700 (PDT) From: Nicholas Piggin To: linuxppc-dev@lists.ozlabs.org Cc: Nicholas Piggin , "Gautham R . Shenoy" , "Vaidyanathan Srinivasan" Subject: [PATCH 05/13] powerpc/64s: interrupt replay balance the return branch predictor Date: Tue, 13 Jun 2017 23:05:49 +1000 Message-Id: <20170613130557.26315-6-npiggin@gmail.com> In-Reply-To: <20170613130557.26315-1-npiggin@gmail.com> References: <20170613130557.26315-1-npiggin@gmail.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , The __replay_interrupt code is branched to with bl, but the caller is returned to directly with rfid from the interrupt. Instead, rfid to a stub that returns to the caller with blr, which should keep the return branch predictor balanced. Reviewed-by: Gautham R. Shenoy Signed-off-by: Nicholas Piggin --- arch/powerpc/kernel/exceptions-64s.S | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S index a04ee0d7f88e..31a9114860c4 100644 --- a/arch/powerpc/kernel/exceptions-64s.S +++ b/arch/powerpc/kernel/exceptions-64s.S @@ -1579,6 +1579,10 @@ doorbell_super_common_msgclr: * Note: While MSR:EE is off, we need to make sure that _MSR * in the generated frame has EE set to 1 or the exception * handler will not properly re-enable them. + * + * Note that we don't specify LR as the NIP (return address) for + * the interrupt because that would unbalance the return branch + * predictor. */ _GLOBAL(__replay_interrupt) /* We are going to jump to the exception common code which @@ -1586,7 +1590,7 @@ _GLOBAL(__replay_interrupt) * we don't give a damn about, so we don't bother storing them. */ mfmsr r12 - mflr r11 + LOAD_REG_ADDR(r11, .L__replay_interrupt_return) mfcr r9 ori r12,r12,MSR_EE cmpwi r3,0x900 @@ -1604,4 +1608,6 @@ FTR_SECTION_ELSE cmpwi r3,0xa00 beq doorbell_super_common_msgclr ALT_FTR_SECTION_END_IFSET(CPU_FTR_HVMODE) +.L__replay_interrupt_return: blr + -- 2.11.0