From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758756AbcJYJDk (ORCPT ); Tue, 25 Oct 2016 05:03:40 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:51196 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758013AbcJYJD2 (ORCPT ); Tue, 25 Oct 2016 05:03:28 -0400 From: Christian Borntraeger To: Peter Zijlstra Cc: Ingo Molnar , Nicholas Piggin , linux-kernel@vger.kernel.org, linux-s390 , linux-arch@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Heiko Carstens , Martin Schwidefsky , Noam Camus , sparclinux@vger.kernel.org, x86@kernel.org, Will Deacon , Catalin Marinas , Russell King , virtualization@lists.linux-foundation.org, xen-devel@lists.xenproject.org, kvm@vger.kernel.org, Christian Borntraeger Subject: [GIT PULL v2 2/5] stop_machine: yield CPU during stop machine Date: Tue, 25 Oct 2016 11:03:12 +0200 X-Mailer: git-send-email 2.5.5 In-Reply-To: <1477386195-32736-1-git-send-email-borntraeger@de.ibm.com> References: <1477386195-32736-1-git-send-email-borntraeger@de.ibm.com> X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16102509-0040-0000-0000-000002F4A311 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16102509-0041-0000-0000-00001D981CD2 Message-Id: <1477386195-32736-3-git-send-email-borntraeger@de.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-10-25_06:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1609300000 definitions=main-1610250152 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Some time ago commit 57f2ffe14fd125c2 ("s390: remove diag 44 calls from cpu_relax()") did stop cpu_relax on s390 yielding to the hypervisor. As it turns out this made stop_machine run really slow on virtualized overcommited systems. For example the kprobes test during bootup took several seconds instead of just running unnoticed with large guests. Therefore, the yielding was reintroduced with commit 4d92f50249eb ("s390: reintroduce diag 44 calls for cpu_relax()"), but in fact the stop machine code seems to be the only place where this yielding was really necessary. This place is probably the most important one as it makes all but one guest CPUs wait for one guest CPU. As we now have cpu_relax_yield, we can use this in multi_cpu_stop. For now lets only add it here. We can add it later in other places when necessary. Signed-off-by: Christian Borntraeger --- kernel/stop_machine.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c index ec9ab2f..1eb8266 100644 --- a/kernel/stop_machine.c +++ b/kernel/stop_machine.c @@ -194,7 +194,7 @@ static int multi_cpu_stop(void *data) /* Simple state machine */ do { /* Chill out and ensure we re-read multi_stop_state. */ - cpu_relax(); + cpu_relax_yield(); if (msdata->state != curstate) { curstate = msdata->state; switch (curstate) { -- 2.5.5