Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752613AbaLAClZ (ORCPT ); Sun, 30 Nov 2014 21:41:25 -0500 Received: from e23smtp08.au.ibm.com ([202.81.31.141]:41376 "EHLO e23smtp08.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752174AbaLAClY (ORCPT ); Sun, 30 Nov 2014 21:41:24 -0500 From: Cyril Bur To: linux-kernel@vger.kernel.org Cc: mpe@ellerman.id.au, akpm@linux-foundation.org, Cyril Bur Subject: [PATCH 2/2] powerpc: add running_clock for powerpc to prevent spurious softlockup warnings Date: Mon, 1 Dec 2014 13:39:00 +1100 Message-Id: <1417401540-12121-3-git-send-email-cyrilbur@gmail.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1417401540-12121-1-git-send-email-cyrilbur@gmail.com> References: <1417401540-12121-1-git-send-email-cyrilbur@gmail.com> X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14120102-0029-0000-0000-000000B74F74 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On POWER8 virtualised kernels the VTB register can be read to have a view of time that only increases while the guest is running. This will prevent guests from seeing time jump if a guest is paused for significant amounts of time. On POWER7 and below virtualised kernels stolen time is subtracted from sched_clock as a best effort approximation. This will not eliminate spurious warnings in the case of a suspended guest but may reduce the occurance in the case of softlockups due to host over commit. Bare metal kernels should avoid reading the VTB as KVM does not restore sane values when not executing. sched_clock is returned in this case. Signed-off-by: Cyril Bur --- arch/powerpc/kernel/time.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c index 7505599..839aeae 100644 --- a/arch/powerpc/kernel/time.c +++ b/arch/powerpc/kernel/time.c @@ -621,6 +621,30 @@ unsigned long long sched_clock(void) return mulhdu(get_tb() - boot_tb, tb_to_ns_scale) << tb_to_ns_shift; } +unsigned long long running_clock(void) +{ + /* + * Don't read the VTB as a host since KVM does not switch in host timebase + * into the VTB when it takes a guest off the CPU, reading the VTB would + * result in reading 'last switched out' guest VTB. + */ + + if (firmware_has_feature(FW_FEATURE_LPAR)) { + if (cpu_has_feature(CPU_FTR_ARCH_207S)) + return mulhdu(get_vtb() - boot_tb, tb_to_ns_scale) << tb_to_ns_shift; + + /* This is a next best approximation without a VTB. */ + return sched_clock() - cputime_to_nsecs(kcpustat_this_cpu->cpustat[CPUTIME_STEAL]); + } + + /* + * On a host which doesn't do any virtualisation TB *should* equal VTB so + * it makes no difference anyway. + */ + + return sched_clock(); +} + static int __init get_freq(char *name, int cells, unsigned long *val) { struct device_node *cpu; -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/