Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752517AbaBMRAt (ORCPT ); Thu, 13 Feb 2014 12:00:49 -0500 Received: from youngberry.canonical.com ([91.189.89.112]:53784 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751397AbaBMRAs (ORCPT ); Thu, 13 Feb 2014 12:00:48 -0500 Message-ID: <52FCFA23.4060701@canonical.com> Date: Thu, 13 Feb 2014 18:00:19 +0100 From: Stefan Bader User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Peter Zijlstra CC: Borislav Petkov , Paolo Bonzini , Linux Kernel Mailing List , kvm@vger.kernel.org, Marcelo Tosatti , MASAO TAKAHASHI , Joerg Roedel Subject: Re: Another preempt folding issue? References: <52FA6D4B.7020709@canonical.com> <20140211194553.GZ9987@twins.programming.kicks-ass.net> <52FB2EC8.4080602@canonical.com> <20140212103713.GE3545@laptop.programming.kicks-ass.net> <20140212104017.GA5121@pd.tnic> <52FB5669.7090506@canonical.com> <20140212115412.GW27965@twins.programming.kicks-ass.net> In-Reply-To: <20140212115412.GW27965@twins.programming.kicks-ass.net> X-Enigmail-Version: 1.5.2 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="U3Q7gDoD1Dm5ktrann9qFgg69dsH44EF1" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --U3Q7gDoD1Dm5ktrann9qFgg69dsH44EF1 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On 12.02.2014 12:54, Peter Zijlstra wrote: > On Wed, Feb 12, 2014 at 12:09:29PM +0100, Stefan Bader wrote: >> Something else here I run a kernel with CONFIG_PREEMPT not set and NR_= CPUS >> limited to 8 (for the 32bit kernel). So the default apic driver is use= d. Since >> default_send_IPI_mask_logical is only used from there, I assume the tr= ace you >> got does the same. Maybe something there is wrong which would explain = why we >> only see it on 32bit hosts. >=20 > Can you try with a different APIC driver to test this? >=20 I don't think I can. And I think the statement about this only be used fo= r 32bit could be wrong. I got mislead to think so because those are only defined = in probe_32 but the 64bit counterpart isn't containing much aside that. Anyway, I played around with tracing a bit more. So with this change: if (need_resched()) { srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx); if (need_resched() !=3D should_resched()) { + trace_printk("need(%i) !=3D should(%i)\n"= , + need_resched(), should_resched())= ; + trace_printk("exit_reason=3D%u\n", + vcpu->run->exit_reason); + trace_printk("preempt_count=3D%lx\n", + __this_cpu_read_4(__preempt_coun= t)); + tracing_stop(); + printk(KERN_ERR "Stopped tracing, due to= inconsistent state.\n"); } + schedule(); - cond_reschedule(); vcpu->srcu_idx =3D srcu_read_lock(&kvm->srcu); } I get the following (weird) output: Xorg-1078 [001] d... 71.270251: native_smp_send_reschedul= e <-resched_task Xorg-1078 [001] d... 71.270251: default_send_IPI_mask_log= ical <-native_smp_send_reschedule bamfdaemon-2318 [001] d... 71.270465: resched_task <-check_pree= mpt_wakeup bamfdaemon-2318 [001] d... 71.270539: resched_task <-check_pree= mpt_wakeup compiz-2365 [001] d... 71.270689: resched_task <-check_pree= mpt_wakeup compiz-2365 [001] d... 71.270827: resched_task <-check_pree= mpt_wakeup compiz-2365 [001] d... 71.270940: resched_task <-check_pree= mpt_wakeup qemu-system-x86-2679 [000] dn.. 71.270999: smp_reschedule_interrupt <-reschedule_interrupt qemu-system-x86-2679 [000] dn.. 71.270999: scheduler_ipi <-smp_reschedule_interrupt qemu-system-x86-2679 [000] .N.. 71.271001: kvm_arch_vcpu_ioctl_run: = need(1) !=3D should(0) qemu-system-x86-2679 [000] .N.. 71.271002: kvm_arch_vcpu_ioctl_run: exit_reason=3D2 qemu-system-x86-2679 [000] .N.. 71.271003: kvm_arch_vcpu_ioctl_run: preempt_count=3D0 So am I reading this right, that the interrupt did get delivered to cpu#0= while the thread info already had the resched flag set. So this really should h= ave cleared the bit in preempt_count. But while the trace info shows 'N' for = some reason should_reschedule returns false but at the same time reading the p= reempt count manually shows it 0? --U3Q7gDoD1Dm5ktrann9qFgg69dsH44EF1 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQIcBAEBCgAGBQJS/PojAAoJEOhnXe7L7s6j3xkQAImlBd6p2Q8Q5Wjf1otvjVdN Hnj4NLY8EEc1zHi5IeQ+1pPLMNcaOMWT4blRiqNGMzGEeX8+XFKfzaxY/UtMui1t v7QPAD9TTh6Prp87yK9Qeq79UhaxkElZG7ZuVb7DBGzRyPDFiNaj4XsyBaU9cDS+ FsCxhUBAKYqsjZSd5Tj4/Hmq/SjtobepPK+rBVOPndj4eqWiRH3Q31GXsVNqfKeE lYhgs490RuKOBMPjguLBnslZV3rhKy+ZWx6jOVNAa2WXQtIIgaGMtyaRgfohM2NL NuJ/1MbE9gjMfQlB/j4t6rsbr3snhb5zpLKkqllkeMrGl2V+gyzBu+nI9Fgu2bUP 2A7CpSBwZOlNo2Aw3BvpTkkLLJituQrQFIdgvD+2XQ1v7e9agccQqp7Pfu/QfPMn 6SMApp36ayFTAAvIFRocNGClsjQTwHzgVi24wNTp19yoMYGcIDIURbaPcJPH0heT HoyvTz7UMomouOKLGA+X516xEdlsxHk7v+F+LByHusbQhSeRpjySEhHR7NOLqnZ1 A8YqmL3KTaG/iLXjlEtA3mDFD6IVHZ6RrRUtI+GHuyTnrFufQj6C0jcQRU8P++/L 9fb6nJdzHfPh1htk4GH1/tYt6+Nm46xGIm0+Yzv/WRZOiC4Q/HvYRhJXc6eF5pYM F8oQsdLWBrEZy9HF2amE =QD7P -----END PGP SIGNATURE----- --U3Q7gDoD1Dm5ktrann9qFgg69dsH44EF1-- -- 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/