From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [PATCH v4: kvm 2/4] Kill the confusing tsc_ref_khz and ref_freq variables. Date: Fri, 09 Oct 2009 22:47:52 +0200 Message-ID: <4ACFA178.2040203@web.de> References: <4AC1C59F.6010703@redhat.com> <1254260317-3490-1-git-send-email-zamsden@redhat.com> <1254260317-3490-2-git-send-email-zamsden@redhat.com> <4ACE734D.10600@web.de> <4ACF9C9B.2040006@redhat.com> <4ACF9EC3.2050901@web.de> <4ACF9EDF.5000808@redhat.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enig3BE09A1B500EF657D60BBA35" Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Avi Kivity , Marcelo Tosatti To: Zachary Amsden Return-path: In-Reply-To: <4ACF9EDF.5000808@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig3BE09A1B500EF657D60BBA35 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Zachary Amsden wrote: > On 10/09/2009 10:36 AM, Jan Kiszka wrote: >> Zachary Amsden wrote: >> =20 >>> On 10/08/2009 01:18 PM, Jan Kiszka wrote: >>> =20 >>>> Zachary Amsden wrote: >>>> >>>> =20 >>>>> They are globals, not clearly protected by any ordering or locking,= >>>>> and >>>>> vulnerable to various startup races. >>>>> >>>>> Instead, for variable TSC machines, register the cpufreq notifier a= nd >>>>> get >>>>> the TSC frequency directly from the cpufreq machinery. Not only is= it >>>>> always right, it is also perfectly accurate, as no error prone >>>>> measurement >>>>> is required. >>>>> >>>>> On such machines, when a new CPU online is brought online, it isn't= >>>>> clear what >>>>> frequency it will start with, and it may not correspond to the >>>>> reference, thus >>>>> in hardware_enable we clear the cpu_tsc_khz variable to zero and ma= ke >>>>> sure >>>>> it is set before running on a VCPU. >>>>> >>>>> Signed-off-by: Zachary Amsden >>>>> --- >>>>> arch/x86/kvm/x86.c | 26 ++++++++++++++++---------- >>>>> 1 files changed, 16 insertions(+), 10 deletions(-) >>>>> >>>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >>>>> index 15d2ace..de4ce8f 100644 >>>>> --- a/arch/x86/kvm/x86.c >>>>> +++ b/arch/x86/kvm/x86.c >>>>> @@ -1326,6 +1326,8 @@ out: >>>>> void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu) >>>>> { >>>>> kvm_x86_ops->vcpu_load(vcpu, cpu); >>>>> + if (unlikely(per_cpu(cpu_tsc_khz, cpu) =3D=3D 0)) >>>>> + per_cpu(cpu_tsc_khz, cpu) =3D cpufreq_quick_get(cpu); >>>>> kvm_request_guest_time_update(vcpu); >>>>> } >>>>> >>>>> @@ -3061,9 +3063,6 @@ static void bounce_off(void *info) >>>>> /* nothing */ >>>>> } >>>>> >>>>> -static unsigned int ref_freq; >>>>> -static unsigned long tsc_khz_ref; >>>>> - >>>>> static int kvmclock_cpufreq_notifier(struct notifier_block *nb, >>>>> unsigned long val, >>>>> void *data) >>>>> { >>>>> @@ -3072,14 +3071,11 @@ static int kvmclock_cpufreq_notifier(struct= >>>>> notifier_block *nb, unsigned long va >>>>> struct kvm_vcpu *vcpu; >>>>> int i, send_ipi =3D 0; >>>>> >>>>> - if (!ref_freq) >>>>> - ref_freq =3D freq->old; >>>>> - >>>>> if (val =3D=3D CPUFREQ_PRECHANGE&& freq->old> freq->new)= >>>>> return 0; >>>>> if (val =3D=3D CPUFREQ_POSTCHANGE&& freq->old< freq->new= ) >>>>> return 0; >>>>> - per_cpu(cpu_tsc_khz, freq->cpu) =3D cpufreq_scale(tsc_khz_ref,= >>>>> ref_freq, freq->new); >>>>> + per_cpu(cpu_tsc_khz, freq->cpu) =3D freq->new; >>>>> >>>>> spin_lock(&kvm_lock); >>>>> list_for_each_entry(kvm,&vm_list, vm_list) { >>>>> @@ -3120,12 +3116,14 @@ static void kvm_timer_init(void) >>>>> { >>>>> int cpu; >>>>> >>>>> - for_each_possible_cpu(cpu) >>>>> - per_cpu(cpu_tsc_khz, cpu) =3D tsc_khz; >>>>> if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) { >>>>> - tsc_khz_ref =3D tsc_khz; >>>>> cpufreq_register_notifier(&kvmclock_cpufreq_notifier_blo= ck, >>>>> CPUFREQ_TRANSITION_NOTIFIER); >>>>> + for_each_online_cpu(cpu) >>>>> + per_cpu(cpu_tsc_khz, cpu) =3D cpufreq_get(cpu); >>>>> >>>>> =20 >>>> This doesn't build for !CONFIG_CPU_FREQ. >>>> >>>> =20 >>> And did it before? >>> =20 >> Yes, because cpufreq_get, which is undefined without CONFIG_CPU_FREQ, >> did not exist so far. One may argue that this is a deficit of the >> cpufreq API. However, it needs fixing. >> =20 >=20 > I'll send a patch today. I'm going with API deficient and will fix > that, but this means I will also require a fix for kvm-kmod :( That won't be tricky, I will queue up a fix. BTW, is the KVM prepared for cpufreq_get returning 0? Jan --------------enig3BE09A1B500EF657D60BBA35 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (GNU/Linux) Comment: Using GnuPG with SUSE - http://enigmail.mozdev.org iEYEARECAAYFAkrPoXsACgkQitSsb3rl5xTzYACfYSEiV/asi/G0h1V3PBKCWQkv Ry4AoJ3nSdedYzkL3b9/wMv4PFUe6rRw =tE2d -----END PGP SIGNATURE----- --------------enig3BE09A1B500EF657D60BBA35--