From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752655AbdJFSlN (ORCPT ); Fri, 6 Oct 2017 14:41:13 -0400 Received: from mx0b-00190b01.pphosted.com ([67.231.157.127]:38556 "EHLO mx0b-00190b01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751649AbdJFSlL (ORCPT ); Fri, 6 Oct 2017 14:41:11 -0400 Subject: Re: [PATCH] intel_idle: replace conditionals with static_cpu_has(X86_FEATURE_ARAT) To: Jacob Pan Cc: linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org References: <1507310385-22388-1-git-send-email-jbaron@akamai.com> <20171006113633.0186eb78@jacob-builder> From: Jason Baron Message-ID: Date: Fri, 6 Oct 2017 14:41:07 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <20171006113633.0186eb78@jacob-builder> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-10-06_04:,, signatures=0 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1707230000 definitions=main-1710060258 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-10-06_04:,, signatures=0 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1707230000 definitions=main-1710060259 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/06/2017 02:36 PM, Jacob Pan wrote: > On Fri, 6 Oct 2017 13:19:45 -0400 > Jason Baron wrote: > >> If the 'arat' cpu flag is set, then the conditionals in intel_idle() >> that guard calling tick_broadcast_enter()/exit() will never be true. >> Use static_cpu_has(X86_FEATURE_ARAT) to create a fast path to replace >> the conditional. >> >> Signed-off-by: Jason Baron >> Cc: Jacob Pan >> Cc: Len Brown >> Cc: Rafael J. Wysocki >> --- >> drivers/idle/intel_idle.c | 16 +++++++++++----- >> 1 file changed, 11 insertions(+), 5 deletions(-) >> >> diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c >> index 5dc7ea4..5db5e31 100644 >> --- a/drivers/idle/intel_idle.c >> +++ b/drivers/idle/intel_idle.c >> @@ -913,8 +913,7 @@ static __cpuidle int intel_idle(struct >> cpuidle_device *dev, struct cpuidle_state *state = >> &drv->states[index]; unsigned long eax = flg2MWAIT(state->flags); >> unsigned int cstate; >> - >> - cstate = (((eax) >> MWAIT_SUBSTATE_SIZE) & >> MWAIT_CSTATE_MASK) + 1; >> + bool uninitialized_var(tick); >> >> /* >> * NB: if CPUIDLE_FLAG_TLB_FLUSHED is set, this idle >> transition @@ -923,12 +922,19 @@ static __cpuidle int >> intel_idle(struct cpuidle_device *dev, >> * useful with this knowledge. >> */ >> >> - if (!(lapic_timer_reliable_states & (1 << (cstate)))) >> - tick_broadcast_enter(); >> + if (!static_cpu_has(X86_FEATURE_ARAT)) { >> + cstate = (((eax) >> MWAIT_SUBSTATE_SIZE) & >> + MWAIT_CSTATE_MASK) + 1; >> + tick = false; >> + if (!(lapic_timer_reliable_states & (1 << >> (cstate)))) { >> + tick = true; >> + tick_broadcast_enter(); >> + } >> + } >> >> mwait_idle_with_hints(eax, ecx); >> >> - if (!(lapic_timer_reliable_states & (1 << (cstate)))) >> + if (!static_cpu_has(X86_FEATURE_ARAT) && tick) >> tick_broadcast_exit(); >> >> return index; > > Seems better to have a function pointer set up at init time to select > whether we do tick_broadcast or not (two functions). There is no need to > check CPU feature on every entry. > Hi, static_cpu_has() uses alternatives patching, so the cpu feature is not tested on every entry. With the arat flag set you just have two nops in the straight-line code path with this patch. Thanks, -Jason